Allison

Allison 3000 & 4000 Gen 4 Fault Code: P1892 Throttle Position Sensor (TPS) PWM Signal High Input

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DIAGNOSTIC RESPONSE:
Use default throttle values

CIRCUIT DESCRIPTION:
The Transmission Control Module (TCM) can be calibrated to receive a Pulse Width Modulation (PWM) TPS pedal position signal.

NOTE: A throttle source can be specified by:
1. Autodetect of the throttle source (prior to MY 09 new release calibrations). Calibrations that have rolled forward from a previous software release will continue to have the autodetect source available in later CIN versions.
2. Use of CMC Override Throttle Source with the diagnostic tool to set throttle source (SAE J1939, SAE J1587, PWM, or Autodetect). Choose “Autodetect”‘ from the CMC list only if the calibration is prior to MY 09 or the autodetect feature has rolled into a later CIN version.
3. Communication link type selected during calibration request process for MY 09 and later calibrations.

NOTE: New MY 09 and later calibrations that did not maintain autodetect (i.e., did not roll forward from earlier software) should not be re-programmed by the CMC Override Throttle Source. This disables some datalink features for the calibration’s specified communication link type. If a different throttle source is needed, calibrate with a new CIN that enables the desired throttle source.

The TCM is connected to the TPS by:
PWM TPS signal (W144)

CONDITIONS FOR RUNNING THE DTC:
1. A PWM TPS must be the throttle source.
2. After TCM initializes normally and engine speed is above 200 rpm for more than 5 seconds, this DTC test will run at 0.10 second intervals.
3. DTC P 1892 not active.

CONDITIONS FOR SETTING THE DTC:
DTC P1892 sets if the TCM has been autodetected, forced, or calibrated to receive a PWM TPS signal, and the PWM throttle frequency is more than 95.1 % for more than 5 seconds.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P1892 is active, the following conditions occur:
1. The TCM does not illuminate the CHECK TRANS light, unless January 2010 software or later.
2. DTC is stored in TCM history.
3. Default value used for% throttle is based on engine torque and engine speed.

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
Use the diagnostic tool to clear the DTC from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without failure.

DIAGNOSTIC AIDS:
DTC P1892 indicates the TCM has detected a PWM throttle percentage in the high error zone, and may be caused by the following:
1. Short to battery in W144 circuit
2. PWM TPS source set in calibration or has been autodetected in non-PWM TPS applications
3. PWM TPS source set by CMC Override Throttle Source using the diagnostic tool in non-PWM TPS applications
4. defective PWM TPS
5. TCM issue.
6. TPS not adjusted. Check with OEM for PWM TPS specifications and adjustment procedures.

PWM may be monitored using data monitor in the diagnostic tool version 9.2 or higher. Absolute throttle % should increase and decrease from Closed Throttle (CT) to Wide Open Throttle (WOT).

Review applicable information in Control System and Transmission Specifications to find additional circuit specifications, system and connector diagrams, and troubleshooting tips.

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Allison 3000 & 4000 Gen 4 Fault Code: P2184 Engine Coolant Temperature Sensor Circuit Low Input

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DIAGNOSTIC RESPONSE:
Use default engine coolant values

CIRCUIT DESCRIPTION:
The Transmission Control Module (TCM) receives an input from an Engine Coolant Temperature (ECT) sensor. The TCM supplies a 5V reference voltage signal into a voltage-sensing network that is connected to one side of the ECT sensor on W135. The other side of the ECT sensor is connected to the TCM analog ground on W158.

The resistance value of the ECT sensor determines the voltage drop in the ECT sensor circuit. As resistance changes, the voltage drop across the ECT sensor circuit also changes and varies the ECT sensor input voltage on W135. The TCM uses engine coolant temperature information to restrict retarder operation when an engine coolant overheat condition is detected.

CONDITIONS FOR RUNNING THE DTC:
1. After TCM initializes normally and engine speed is above 200 rpm for more than 5 seconds, this DTC test runs at 0.25 second intervals.
2. Retarder and ECT sensor autodetected or forced present by CMC (Override Retarder Autodetect//Override Engine Coolant Source).
3. This test is disabled for this ignition cycle when a failure is reported for this DTC or DTC P2185.
4. The retarder reduction and preselect, based on engine coolant temperature feature, is enabled in the calibration.

CONDITIONS FOR SETTING THE DTC:
The TCM detects engine coolant temperature greater than 149°C (300°F) for more than 10 seconds.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P2184 is active, the following conditions occur:
1. The TCM does not illuminate the CHECK TRANS light.
2. DTC is stored in TCM history.
3. TCM uses default engine coolant temperature values.

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
Use the diagnostic tool to clear the DTC from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without failure.

DIAGNOSTIC AIDS:
DTC P2184 may be caused by:
1. Incorrect transmission fluid fill.
2. W135 shorted to ground, or shorted to another wire in chassis harness.
3. Broken or defective connector assemblies allowing pushed back pins to short together.
4. Unlocked connectors, missing seal plugs allowing moisture in connectors.
5. Defective ECT sensor.
6. Defective TCM.
7. High transmission fluid temperature.
8. Inadequate or obstructed vehicle cooling system.
9. Non-bypassed engine coolant thermostats that are not opening in time may cause overheat condition for transmission fluid temperature. Monitor transmission fluid temperature using the diagnostic tool and review transmission overheat and retarder information in General Troubleshooting of Performance Complaints.

The ECT sensor resistance is available on the diagnostic tool Data Monitor grid. Prior to ‘Connect’ for the diagnostic tool, check the ‘Troubleshoot Specific Problem’ box under “Connection Options” and then check the ‘Sensor, Voltage, Ohms, and Counts Data’ box.

Check if ECT sensor resistance is increasing, decreasing, or stationary with fluctuations in fluid temperature.

Refer to DTC P2740 and DTC P0218 or General Troubleshooting of Performance Complaints as guidelines for troubleshooting vehicle cooling issues.

Review applicable information in Control System and Transmission Specifications to find additional circuit specifications, system and connector diagrams, and troubleshooting tips.

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Allison 3000 & 4000 Gen 4 Fault Code: P2185 Engine Coolant Temperature Sensor Circuit High Input

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DIAGNOSTIC RESPONSE:
Use default coolant engine values

CIRCUIT DESCRIPTION:
The Transmission Control Module (TCM) receives an input from an Engine Coolant Temperature (ECT) sensor. The TCM supplies a 5V reference voltage signal into a voltage-sensing network that is connected to one side of the ECT sensor on W135. The other side of the ECT sensor is connected to TCM analog ground on W158.

The resistance value of the ECT sensor determines the voltage drop in the ECT sensor circuit. As resistance changes, the voltage drop across the ECT sensor circuit also changes and varies the sensor input voltage on W135. The TCM uses engine coolant temperature information to restrict retarder operation when an engine coolant overheat condition is detected.

CONDITIONS FOR RUNNING THE DTC:
1. After TCM initializes normally and engine speed is above 200 rpm for more than 5 seconds, this DTC test runs at 0.25 second intervals.
2. Retarder and ECT sensor autodetected or forced present by CMC (Override Retarder Autodetect//Override Engine Coolant Source).
3. This test is disabled for this ignition cycle when a failure is reported for this DTC or DTC P2184.
4. The retarder reduction and preselect, based on engine coolant temperature feature, is enabled in the calibration.

CONDITIONS FOR SETTING THE DTC:
The TCM detects engine coolant temperature less than -45°C (-49°F) for more than 10 seconds.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P2185 is active, the following conditions occur:
1. The TCM does not illuminate the CHECK TRANS light.
2. DTC is stored in TCM history.
3. TCM uses default engine coolant temperature values.

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
Use the diagnostic tool to clear the DTC from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without failure.

DIAGNOSTIC AIDS:
NOTE: If DTC P2185 is accompanied by DTC P0713 or P2743, check for short to battery on W135, W154 and W175. Follow DTC P0713 steps first, if in history with this DTC.

DTC P2185 may be caused by:
1. Incorrect transmission fluid fill.
2. W135 shorted to another wire in chassis harness.
3. W135 open circuit in chassis harness.
4. W158 open circuit in chassis harness.
5. Broken or defective connector assemblies that cause pins to short together.
6. Unlocked connectors, missing or damaged seals, missing seal plugs that allow moisture into connectors.
7. Defective ECT sensor.
8. Defective TCM.

The ECT sensor resistance is available on the diagnostic tool Data Monitor grid. Prior to ‘Connect’ for the diagnostic tool, check the ‘Troubleshoot Specific Problem’ box under “Connection Options” and then check the ‘Sensor, Voltage, Ohms, and Counts Data’ box.

Check if ECT sensor resistance is increasing, decreasing, or stationary with fluctuations in fluid temperature. Normal circuit operation is indicated if sensor resistance decreases as fluid temperature increases, and sensor resistance increases as fluid temperature decreases.

Review applicable information in Control System and Transmission Specifications to find additional circuit specifications, system and connector diagrams, and troubleshooting tips.

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Allison 3000 & 4000 Gen 4 Fault Code: P2637 Torque Management Feedback Signal – SEM

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DIAGNOSTIC RESPONSE:
Inhibit SEM

CIRCUIT DESCRIPTION:
Shift Energy Management (SEM) allows the Transmission Control Module {TCM) to request torque reduction from the engine controller. By reducing torque, shifts can be made quicker and at a more consistent output torque, which reduces clutch temperatures allowing increased clutch life. When an engine torque rating exceeds certain limits, Low Range Torque Protection (LRTP) is used. This feature limits engine torque in lower ranges to protect the transmission from damage if a stall condition occurs.

This test detects:
Electronic Control Module (ECM) response to SAE J1939 transmission torque reduction commands during upshifts.

For high torque applications, the engine must support the required messages to allow SEM and LRTP. For low torque applications, SEM may or may not be active.

CONDITIONS FOR RUNNING THE DTC:
1. Upshift in process with driver’s demand engine torque is greater than 80 N·m (59 lb ft).
2. DTC test runs 1 second intervals.
3. This DTC and DTC UO 115 not active.

NOTE: The autodetect drive cycles counter is reset to 0 after TCM recalibration or SEM Reset Auto-Select.

CONDITIONS FOR SETTING THE DTC:
If a SEM engine does not respond to the transmission TSC1 commands to reduce engine torque during upshifts, DTC P2637 becomes active. Upshifts are not required to be consecutive but are in the same drive cycle.

ACTION TAKEN WHEN THE DTC SETS:
1. The CHECK TRANS light illuminates.
2. DTC is stored in the TCM history.
3. Clutch pressures are increased, which may result in shift quality issues.
4. Some shifts may be inhibited.
5. The TCM freezes shift adapts (DNA).
6. The TCM inhibits TCC engagement.
7. DTCs P0614 and/or P2641 may also be active.

CONDITIONS FOR CLEARING THE DTC:
The TCM will continue attempting to use SEM, and will self-clear the active DTC if engine response returns to within acceptable criteria for a number of shifts.

Use the diagnostic tool to clear the DTC from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without the DTC recurring.

DIAGNOSTIC AIDS:
DTC P2637 may be caused by:
1. Incorrect engine calibration.
2. Incorrect transmission calibration.
3. Engine calibration that does not support all required SAE J1939 SEM/LRTP messages.
4. Communication link problem.
5. Vehicle controller (such as a headway controller) preventing transmission control of the engine during the shift process.
6. Defective TCM.

Review applicable information in the OEM Technician’s Library, General Troubleshooting of Performance Complaints, Shift Selector Issues, Control System and Transmission Specifications, and other related information.

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Allison 3000 & 4000 Gen 4 Fault Code: P2641 Torque Management Feedback Signal – LRTP

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DIAGNOSTIC RESPONSE:
Inhibit LRTP

CIRCUIT DESCRIPTION:
Lower Range Torque Protection (LRTP) is an Engine Management function that reduces engine torque when transmission input power, input torque, converter torque output, or converter speed ratio exceeds defined limits. These limits typically occur during torque converter mode or operation in lower gears, where stall or drivetrain torque may reach levels above gearbox capacity. The Transmission Control Module (TCM) only activates LRTP when connected with a compatible electronic engine and control system.

This test detects:
If the engine Electronic Control Module (ECM) responds to SAE J1939 transmission torque reduction commands.

For high torque applications, the engine must support the required messages to allow LRTP. For low torque applications, LRTP may or may not be active.

CONDITIONS FOR RUNNING THE DTC:
1. Net engine torque is greater than 500 N·m (369 lb ft).
2. Shift is not in process.
3. This DTC and DTC U0115 not active.

CONDITIONS FOR SETTING THE DTC:
LRTP enabled engines has net engine torque values exceeding LRTP torque limit for more than 5 seconds.

ACTION TAKEN WHEN THE DTC SETS:
1. The CHECK TRANS light illuminates.
2. DTC is stored in the TCM history.
3. Transmission sends default torque limit and/or stop transmission broadcast of SAE J1939/71 ETC1.
4. The TCM freezes shift adapts (DNA).
5. The TCM inhibits TCC engagement.
6. DTCs P0614 and/or P2637 may also be active.

CONDITIONS FOR CLEARING THE DTC:
The TCM will continue attempting to use LRTP, and will self-clear the active DTC if engine response returns to within acceptable criteria.

Use the diagnostic tool to clear the DTC from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without the DTC recurring.

DIAGNOSTIC AIDS:
DTC P2641 may be caused by:
1. Incorrect engine calibration.
2. Incorrect transmission calibration.
3. Engine calibration that does not support all required SAE J1939 LRTP messages.
4. Communication link problem.
5. Vehicle controller (such as a headway controller) preventing transmission control of the engine during the shift process.
6. Defective TCM.

Review applicable information in the OEM Technician’s Library, General Troubleshooting Of Performance Complaints Shift Selector Issues, Control System and Transmission Specifications, and other related information.


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Allison 3000 & 4000 Gen 4 Fault Code: P2669 Actuator Supply Voltage 2 (HSD2) Open

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DIAGNOSTIC RESPONSE:
SOL OFF, Inhibit TCC operation, Inhibit main modulation, DNA

CIRCUIT DESCRIPTION:
The high side drivers are connected to the high side circuits of the solenoids and commanded on during normal operation. The high side drivers serve as a master switch to supply battery voltage to the low side drivers. High side drivers are turned on during TCM initialization and remain on during normal operation. High side drivers are turned off during cranking and for certain diagnostic responses. The open circuit diagnostic is determined by monitoring the status of the low side drivers. If two or more of the low side drivers circuits are detected by the TCM in a failed open/low state that are supplied by a particular high side driver circuit, the problem is assumed to be on the high side of the load and a high side driver fault becomes active instead of two or more low side driver faults becoming active. There may or may not be low side driver faults present with this DTC. High Side Driver 2 (HSD2) supplies battery voltage to the Pressure Control Solenoid 1 (PCS1), Pressure Control Solenoid 2 (PCS2), Pressure Control Solenoid 3 (PCS3), and Shift Solenoid 1 (SS1) via wire 171. The TCM regulates control current to the solenoids by switching the appropriate low side driver on and off.

CONDITIONS FOR RUNNING THE DTC:
1. DTC enabled with ignition ON, engine OFF, and battery voltage greater than 9 volts.
2. HSD2 is commanded ON.
3. DTC disabled while engine is cranking longer than 4 seconds, and battery voltage is less than 10 volts.
4. DTC re-enabled once engine is running and TCM is initialized normally.

CONDITIONS FOR SETTING THE DTC:
This DTC sets when the TCM detects two or more low side drivers connected to HSD2, e.g., PCS1, PCS2, PCS3, or SS 1 low side drivers have been detected in a failed low state and HSD2 voltage is less than 6 volts.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P2669 is active:
1. The DTC sets while in a forward range, then shifts to another forward range. If failure occurs while in Neutral (N), the transmission remains in Neutral (N). If failure occurs while in Reverse (R), the transmission remains in Reverse (R) or shifts to Neutral (N). Once range is attained, transmission is locked in this range and there is no response to shift selector requests.
2. The TCM inhibits TCC engagement.
3. Main Modulation is inhibited.
4. DTC is stored in the TCM history.
5. The CHECK TRANS light illuminates.
6. The TCM freezes shift adapts (DNA).

CONDITIONS FOR CLEARING THE DTC:
Use the diagnostic tool to clear the DTC from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without failure.

DIAGNOSTIC AIDS:
DTC P2669 can be caused by:
1. HSD2 circuit issues such as:
– W171 shorted to another wire in chassis harness.
– W171 (terminal 6 of 20-way) shorted to another wire in the internal transmission harness.
– W171 high resistance or an open circuit in chassis harness.
– W171 (terminal 6 of 20-way) high resistance or an open circuit in internal transmission harness.
2. Two or more low side driver circuit issues with PCS1, PCS2, PCS3, or SS1.
3. PCS1 issues such as:
– W136 shorted to another wire in chassis harness.
– W136 shorted (terminal 4 of 20-way) to another wire in the internal transmission harness.
– W136 high resistance or an open circuit in chassis harness.
– W136 (terminal 4 of 20-way) high resistance or an open circuit in internal transmission harness.
4. PCS2 issues such as:
– W152 shorted to another wire in chassis harness.
– W152 shorted (terminal 5 of 20-way) to another wire in the internal transmission harness.
– W152 high resistance or an open circuit in chassis harness.
– W152 (terminal 5 of 20-way) high resistance or an open circuit in internal transmission harness.
5. PCS3 issues such as:
– W133 shorted to another wire in chassis harness.
– W133 shorted (terminal 9 of 20-way) to another wire in the internal transmission harness.
– W133 high resistance or an open circuit in chassis harness.
– W133 (terminal 9 of 20-way) high resistance or an open circuit in internal transmission harness.
6. SS 1 issues such as:
– W151 shorted to another wire in chassis harness.
– W151 shorted (terminal 10 of 20-way) to another wire in the internal transmission harness.
– W151 high resistance or an open circuit in chassis harness.
– W151 high resistance or an open circuit (terminal 10 of 20-way) in internal transmission harness.
7. Defective solenoids PCS1, PCS2, PCS3, SS1.
8. Unlocked connectors, expanded terminals, poor pin crimps or unlocked pins causing high resistance or open circuit.
9. Defective TCM.

Review applicable information in Control System and Transmission Specifications to find additional circuit specifications, system and connector diagrams, and troubleshooting tips.

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Allison 3000 & 4000 Gen 4 Fault Code: P2670 Actuator Supply Voltage 2 (HSD2) Low

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DIAGNOSTIC RESPONSE:
Yes DNS, SOL OFF (hydraulic default)

CIRCUIT DESCRIPTION:
The high side drivers are connected to the high side circuits of the solenoids and commanded on during normal operation. The high side drivers serve as a master switch to supply battery voltage to the low side drivers. High side drivers are turned on during TCM initialization and remain on during normal operation. High side drivers are turned off during cranking and for certain diagnostic responses. The low circuit diagnostic is determined by monitoring the status of the low side drivers and high side drivers voltage. If two or more of the low side drivers circuits are detected by the TCM in a failed low state that are supplied by a particular high side driver circuit, and the high side drivers voltage is below 6V, the problem is assumed to be on the high side of the load and a high side driver fault becomes active instead of two or more low side driver faults becoming active. There may or may not be low side driver faults present with this DTC. High Side Driver 2 (HSD2) supplies battery voltage to the Pressure Control Solenoid 1 (PCS1), Pressure Control Solenoid 2 (PCS2), Pressure Control Solenoid 3 (PCS3), and Shift Solenoid 1 (SS1) via wire 171. The TCM regulates control current to the solenoids by switching the appropriate low side driver on and off.

CONDITIONS FOR RUNNING THE DTC:
1. DTC enabled with ignition ON, engine OFF, and battery voltage greater than 9 volts.
2. HSD2 is commanded ON.
3. DTC disabled while engine is cranking longer than 4 seconds, and battery voltage is less than 10 volts.
4. DTC re-enabled once engine is running and TCM is initialized normally.

CONDITIONS FOR SETTING THE DTC:
This DTC sets when the TCM detects two or more low side drivers connected to HSD2, e.g., PCS1, PCS2, PCS3, or SS 1 low side drivers have been detected in a failed low state and HSD2 voltage is less than 6 volts.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P2670 is active:
1. The DTC sets while in a forward range, then shifts to another forward range. If failure occurs while in Neutral (N), the transmission remains in Neutral (N). If failure occurs while in Reverse (R), the transmission remains in Reverse (R) or shifts to Neutral (N). Once range is attained, transmission is locked in this range and there is no response to shift selector requests.
2. The TCM inhibits TCC engagement.
3. Main Modulation is inhibited.
4. DTC is stored in the TCM history.
5. The CHECK TRANS light illuminates.
6. The TCM freezes shift adapts (DNA).

CONDITIONS FOR CLEARING THE DTC:
Use the diagnostic tool to clear the DTC from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without failure.

DIAGNOSTIC AIDS:
DTC P2670 can be caused by:
1. HSD2 circuit issues such as:
– W171 shorted to another wire in chassis harness.
– W171 (terminal 6 of 20-way) shorted to another wire in the internal transmission harness.
2. Two or more low side driver circuit issues with HSD2, PCS1, PCS2, PCS3, or SS1.
3. PCS1 issues such as:
– W136 shorted to another wire in chassis harness.
– W136 shorted (terminal 4 of 20-way) to another wire in the internal transmission harness.
– PCS 1 shorted.
4. PCS2 issues such as:
– W152 shorted to another wire in chassis harness.
– W152 shorted (terminal 5 of 20-way) to another wire in the internal transmission harness.
– PCS2 shorted.
5. PCS3 issues such as:
– W133 shorted to another wire in chassis harness.
– W133 shorted (terminal 9 of 20-way) to another wire in the internal transmission harness.
– PCS3 shorted.
6. SS 1 issues such as:
– W151 shorted to another wire in chassis harness.
– W151 shorted (terminal 10 of 20-way) to another wire in the internal transmission harness.
– SS 1 shorted.
7. Broken or defective connector assemblies allowing pushed back pins to short together.
8. Unlocked connectors, expanded terminals, unlocked pins, causing open circuit in connectors.
9. Defective TCM.

Review applicable information in Control System and Transmission Specifications to find additional circuit specifications, system and connector diagrams, and troubleshooting tips.

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Allison 3000 & 4000 Gen 4 Fault Code: P2671 Actuator Supply Voltage 2 (HSD2) High

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DIAGNOSTIC RESPONSE:
DNS, SOL OFF (hydraulic default)

CIRCUIT DESCRIPTION:
The high side drivers are connected to the high side circuits of the solenoids and commanded on during normal operation. The high side drivers serve as a master switch to supply battery voltage to the low side drivers. High side drivers are turned on during TCM initialization and remain on during normal operation. High side drivers are turned off during cranking and for certain diagnostic responses. High Side Driver 2 (HSD2) supplies battery voltage to the Pressure Control Solenoid 1 (PCS1), Pressure Control Solenoid 2 (PCS2), Pressure Control Solenoid (PCS3), and Shift Solenoid 1 (SS1) via wire 171. The TCM regulates control current to the solenoids by switching the appropriate low side driver on and off. This test detects if the voltage measured at the HSD2 detection circuit indicates high during initialization when the circuit is off.

CONDITIONS FOR RUNNING THE DTC:
During TCM initialization while high side driver is commanded off.

CONDITIONS FOR SETTING THE DTC:
This DTC sets during TCM initialization, if HSD2 voltage detected to be greater than 6V while HSD2 circuit is OFF.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P2671 is active:
1. Transmission fails to Neutral (N).
2. DTC is stored in the TCM history.
3. The CHECK TRANS light illuminates.
4. The TCM freezes shift adapts (DNA).

CONDITIONS FOR CLEARING THE DTC:
Use the diagnostic tool to clear the DTC from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without failure.

DIAGNOSTIC AIDS:
DTC P2671 can be caused by:
1. HSD2 circuit issues such as:
– W171 shorted to another wire in chassis harness.
– W171 (terminal 6 of 20-way) shorted to another wire in the internal transmission harness.
2. Two or more low side driver circuit issues with PCS1, PCS2, PCS3, or SS1.
3. PCS 1 issues such as:
– W136 shorted to another wire in chassis harness.
– W136 shorted (terminal 4 of 20-way) to another wire in the internal transmission harness.
4. PCS2 issues such as:
– W152 shorted to another wire in chassis harness.
– W152 shorted (terminal 5 of 20-way) to another wire in the internal transmission harness.
5. PCS3 issues such as:
– W133 shorted to another wire in chassis harness.
– W133 shorted (terminal 9 of 20-way) to another wire in the internal transmission harness.
6. SS 1 issues such as:
– W151 shorted to another wire in chassis harness.
– W151 shorted (terminal 10 of 20-way) to another wire in the internal transmission harness.
7. Broken or defective connector assemblies allowing pushed back pins to short together.
8. Unlocked connectors, missing seal plugs allowing moisture in connectors.
9. Defective TCM.

Review applicable information in Control System and Transmission Specifications to find additional circuit specifications, system and connector diagrams, and troubleshooting tips.

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Allison 3000 & 4000 Gen 4 Fault Code: P2684 Actuator Supply Voltage 3 (HSD3) Open

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DIAGNOSTIC RESPONSE:
SOL OFF, Inhibit TCC operation, Inhibit main modulation, DNA

CIRCUIT DESCRIPTION:
The high side drivers are connected to the high side circuits of the solenoids and commanded on during normal operation. The high side drivers serve as a master switch to supply battery voltage to the low side drivers. High side drivers are turned on during TCM initialization and remain on during normal operation. High side drivers are turned off during cranking and for certain diagnostic responses. The open circuit diagnostic is determined by monitoring the status of the low side drivers. If two or more of the low side drivers circuits are detected by the TCM in a failed open/low state that are supplied by a particular high side driver circuit, the problem is assumed to be on the high side of the load and a high side driver fault becomes active instead of two or more low side driver faults becoming active. There may or may not be low side driver faults present with this DTC. High Side Driver 3 (HSD3) supplies battery voltage to the Torque Converter Clutch (TCC) solenoid, Pressure Control Solenoid 5 (PCS5) (retarder or speed models), and Shift Solenoid 2 (SS2) via wire 131. The TCM regulates control current to the solenoids by switching the appropriate low side driver on and off.

CONDITIONS FOR RUNNING THE DTC:
1. DTC enabled with ignition ON, engine OFF, and battery voltage greater than 9 volts.
2. HSD3 is commanded ON.
3. DTC disabled while engine is cranking if longer than 4 seconds, cranking while battery voltage is less than 10 volts.
4. DTC re-enabled once engine is running and TCM is initialized normally.

CONDITIONS FOR SETTING THE DTC:
This DTC sets when the TCM detects two or more low side drivers connected to HSD3; e.g., TCC, PCS5, SS2, air solenoid (SS2) low side drivers, have been detected in a failed low/open state while HSD3 voltage is greater than 6 volts.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P2684 is active:
1. For 7-speed models, limit ranges to Reverse (R), Neutral (N) and ranges 2-6 operation.
2. TCM commands retarder OFF.
3. The TCM inhibits TCC engagement.
4. DTC is stored in the TCM history.
5. The CHECK TRANS light illuminates.
6. The TCM freezes shift adapts (DNA).

CONDITIONS FOR CLEARING THE DTC:
Use the diagnostic tool to clear the DTC from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without failure.

DIAGNOSTIC AIDS:
DTC P2684 can be caused by:
1. HSD3 circuit issues such as:
– W131 shorted to another wire in chassis harness.
– W131 (terminal 11 of 20-way) shorted to another wire in the internal transmission harness.
– W131 high resistance or an open circuit in chassis harness.
– W131 (terminal 11 of 20-way) high resistance or an open circuit in internal transmission harness.
2. TCC issues such as:
– W137 shorted to another wire in chassis harness.
– W137 shorted (terminal 12 of 20-way) to another wire in the internal transmission harness.
– W137 high resistance or an open circuit in chassis harness.
– W137 (terminal 12 of 20-way) high resistance or an open circuit in internal transmission harness.
3. PCS5 (7-speed Differential Lock, retarder) issues such as:
– W115 shorted to another wire in chassis harness.
– W115 high resistance or an open circuit in chassis harness.
4. SS2 issues such as:
– W119 shorted to another wire in chassis harness.
– W119 shorted (terminal 17 of 20-way) to another wire in the internal transmission harness.
– W119 high resistance or an open circuit in chassis harness.
– W119 (terminal 17 of 20-way) high resistance or an open circuit in internal transmission harness.
5. Air solenoid (SS2) issues such as:
– W119 shorted to another wire in chassis harness.
– W119 high resistance or an open circuit in chassis harness.
6. Defective solenoids TCC, PCS5 (retarder or diff lock), SS2 (air solenoid or C6 solenoid for 7-speed models).
7. Unlocked connectors, expanded terminals, poor pin crimps or unlocked pins causing high resistance or open circuit.
8. Defective TCM.

Review applicable information Control System and Transmission Specifications to find additional circuit specifications, system and connector diagrams, and troubleshooting tips.

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Allison 3000 & 4000 Gen 4 Fault Code: P2685 Actuator Supply Voltage 3 (HSD3) Low

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DIAGNOSTIC RESPONSE:
DNS, SOL OFF (hydraulic default)

CIRCUIT DESCRIPTION:
The high side drivers are connected to the high side circuits of the solenoids and commanded on during normal operation. The high side drivers serve as a master switch to supply battery voltage to the low side drivers. High side drivers are turned on during Transmission Control Module (TCM) initialization, and remain on during normal operation. High side drivers are turned off during cranking and certain diagnostic responses. The low circuit diagnostic is determined by monitoring the status of the low and high side drivers voltage. If two or more of the low side driver circuits are detected by the TCM in a failed low state that are supplied by a particular high side driver circuit, and the high side drivers voltage is below 6V, the problem is assumed to be on the high side of the load and high side driver fault becomes active instead of two or more low side driver faults becoming active. There may or may not be low side driver faults present with this DTC. High Side Driver 3 (HSD3) supplies battery voltage to the Torque Converter Clutch (TCC) solenoid, Pressure Clutch Solenoid 5 (PCS5), and Shift Solenoid 2 (SS2) via W131. The TCM regulates control current to the solenoids by switching the appropriate low side driver on and off.

CONDITIONS FOR RUNNING THE DTC:
1. DTC enabled with ignition ON, engine OFF, and battery voltage greater than 9 volts.
2. HSD3 is commanded ON.
3. DTC disabled while engine is cranking longer than 4 seconds, and the battery voltage is less than 10 volts.
4. DTC re-enabled once engine is running and TCM is initialized normally.

CONDITIONS FOR SETTING THE DTC:
This DTC sets when the TCM detects two or more low side drivers connected to HSD3 (e.g., TCC, PCS5, air solenoid (SS2) low side drivers) have been detected in a failed low state and HSD3 voltage is less than 6 volts.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P2685 is active:
1. For 7-speed, limit ranges to Reverse (R), Neutral (N), and ranges 2-6 operation.
2. TCM commands retarder OFF.
3. The TCM inhibits TCC engagement.
4. DTC is stored in the TCM history.
5. The CHECK TRANS light illuminates.
6. The TCM freezes shift adapts (DNA).

CONDITIONS FOR CLEARING THE DTC:
Use the diagnostic tool to clear the DTC from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without failure.

DIAGNOSTIC AIDS:
DTC P2685 can be caused by:
1. HSD3 circuit issues such as:
– W131 shorted to another wire in chassis harness or to chassis ground.
– W131 (terminal 11 of 20-way) shorted to another wire in the internal transmission harness or to the
control module.
2. TCC issues such as:
– W137 shorted to another wire in chassis harness or to chassis ground.
– W137 shorted (terminal 12 of 20-way) to another wire in the internal transmission harness or to the
control module.
3. PCS5 (7-speed Differential Lock, retarder) issues such as:
– W115 shorted to another wire in chassis harness or to chassis ground.
4. SS2 issues such as:
– W119 shorted to another wire in chassis harness or to chassis ground.
– W119 shorted (terminal 17 of 20-way) to another wire in the internal transmission harness or to the
control module.
5. Air solenoid (SS2) issues such as:
– W119 shorted to another wire in chassis harness or to chassis ground.
6. Defective solenoids TCC, retarder solenoid (PCS5), air solenoid (SS2), or differential lock solenoid (PCS5).
7. Broken or defective connector assemblies allowing pushed back pins to short together.
8. Unlocked connectors, missing seal plugs allowing moisture in connectors.
9. Defective TCM.

Review applicable information in Control System and Transmission Specifications to find additional circuit specifications, system and connector diagrams, and troubleshooting tips.

Read more →

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