Allison

Allison 1000 & 2000 Gen 4 Fault Codes: P0727 Engine Speed Input Circuit No Signal

CIRCUIT DESCRIPTION:
The speed sensors are variable reluctance devices which convert mechanical motion to an AC voltage. Each sensor consists of a wire coil wrapped around a pole piece that is adjacent to a permanent magnet. These elements are contained in a housing which is mounted adjacent to a rotating ferrous member. Two signal wires extend from one end of the housing and an exposed end of the pole piece is at the opposite end of the housing. The permanent magnet produces lines of flux around the pole piece. As a ferrous object (such as a gear tooth) approaches and passes through the gap at the end of the pole piece, an AC voltage pulse is induced in the wire coil. The Transmission Control Module (TCM) calculates the frequency of these AC pulses and converts it to a speed value. The AC voltage generated varies from 150mV at low speed to 15V at high speed. The signal wires from the sensor are formed as twisted pairs to cancel magnetically induced fields. The cable is also shielded to protect from voltage-related fields. Noise from other sources is eliminated by using two-wire differential inputs at the TCM.

CONDITIONS FOR RUNNING THE DTC:
1. The components are powered and ignition voltage is greater than 9V and less than 18V (12V TCM) or greater than 18V and less than 32V (24V TCM).
2. DTC P0716, P0717, or P0726 is not active.
3. Unrealistically low engine speed detected.
4. Engine is running.
5. Transmission turbine speed is at or above 400 rpm.
6. Ignition is in the ON position.

CONDITIONS FOR SETTING THE DTC:
DTC P0727 is set when one of the following conditions occur:
1. Unrealistic large change in engine speed. Failure pending is set if an unrealistic change in engine speed is detected at or above 1140 rpm.
2. Unrealistic low value in engine speed. Failure is set if engine speed is detected below 61 rpm for 4 seconds.

ACTION TAKEN WHEN THE DTC SETS:
1. The TCM defaults engine speed to turbine speed. Turbine speed is used to determine missing engine speed.
2. TCM inhibits TCC momentarily.
3. DTC P0727 is stored in TCM history

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
A Scan Tool may be used to clear the code 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:
Inspect the wiring for poor electrical connections at the TCM. Look for the following conditions:
1. A bent terminal.
2. A backed-out terminal.
3. A damaged terminal.
4. Poor terminal tension.
5. A chafed wire.
6. A broken wire inside the insulation.

You may have to drive the vehicle in order to experience a fault.

If the condition is intermittent, connect the Scan Tool and select the speed sensor indicated by the code. If the signal is erratic, investigate and eliminate the following:
1. Intermittent wiring connection.
2. Excessive vibration (driveline or engine torsionals).
3. Irregular sensor gap (loose sensor, loose tone wheel, or damaged tone wheel.

Install a known good speed sensor and see if normal function is restored to rule out an internal short or open in the sensor removed.

Check that the speed sensor wiring consists of twisted pairs at the rate of 12 to 16 twists per 300 mm. These twists must extend the entire length of the wiring harness to within at least 50 mm of the speed sensor connector.

Install a known good TCM, if available. If the DTC does not return, reinstall the old TCM to verify the repair.

Allison 1000 & 2000 Gen 4 Fault Codes: P0731 Incorrect 1st Gear Ratio

CIRCUIT DESCRIPTION:
The Transmission Control Module (TCM) uses input from the turbine speed sensor and output speed sensor to determine gear ratios. The TCM then compares the known gear ratio to the calculated gear ratio for the current range.

CONDITIONS FOR RUNNING THE DTC:
1. Output speed exceeds 200 rpm.
2. First range is selected and attained.
3. DTC P0716, P0717, P0721, or P0722 is not active.

CONDITIONS FOR SETTING THE DTC:
DTC P0731 sets when the calculated first range ratio (steady state) differs from the known first range ratio.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P0731 is active, the following conditions will occur:
1. The transmission will fail to 2nd or 5th range.
2. If the shift selector is moved to N (Neutral), the transmission will shift to N (Neutral).
3. If the shift selector is moved to R (Reverse), the transmission will shift to R (Reverse) unless the transmission is compromised by overspeeding or a direction change; then it will lock in N (Neutral).

DTC P0731 is stored in the TCM history.

The CHECK TRANS light illuminates.

The TCM freezes shift adapts (DNA).

The TCM inhibits TCC engagement.

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
A Scan Tool may be used to clear the code 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:
1. Incorrect ratio codes typically indicate mechanical problems with specific clutches, i.e. C1 or C5 for 1st range.
2. An incorrect ratio code could indicate a hydraulically failed solenoid. Check the DTC information for the specific solenoid.
3. You may have to drive the vehicle to experience the fault. Clutch test mode can be used to check stall speed.
4. Incorrect TCM calibrations will cause this DTC to set. Verify that the proper TCM calibration is being used with the correct transmission family (there are different gear ratios for the 1000 and 2000 Product Families transmissions).

Allison 1000 & 2000 Gen 4 Fault Codes: P0732 Incorrect 2nd Gear Ratio

CIRCUIT DESCRIPTION:
The Transmission Control Module (TCM) uses input from the turbine speed sensor and output speed sensor to determine gear ratios. The TCM then compares the known gear ratio to the calculated gear ratio for the current range.

CONDITIONS FOR RUNNING THE DTC:
1. Output speed exceeds 200 rpm.
2. Second range is selected and attained.
3. DTC P0716, P0717, P0721, or P0722 is not active.

CONDITIONS FOR SETTING THE DTC:
DTC P0732 sets when the calculated second range ratio (steady state) differs from the known second range ratio.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P0732 is active, the following conditions will occur:
1. The transmission will fail to 3rd range.
2. If the shift selector is moved to N (Neutral), the transmission will shift to N (Neutral).
3. If the shift selector is moved to R (Reverse), the transmission will shift to R (Reverse) unless the transmission is compromised by overspeeding or a direction change; then it will lock in N (Neutral).

DTC P0732 is stored in the TCM history.

The CHECK TRANS light illuminates.

The TCM freezes shift adapts (DNA).

The TCM inhibits TCC engagement.

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
A Scan Tool may be used to clear the code 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:
1. Incorrect ratio codes typically indicate mechanical problems with specific clutches, i.e. C1 and C4 for 2nd range.
2. An incorrect ratio code could indicate a hydraulically failed solenoid. Check the DTC information for the specific solenoid.
3. You may have to drive the vehicle to experience the fault. Clutch test mode can be used to check stall speed.
4. Incorrect TCM calibrations will cause this DTC to set. Verify that the proper TCM calibration is being used with the correct transmission family (there are different gear ratios for the 1000 and 2000 Product Families transmissions).

Allison 1000 & 2000 Gen 4 Fault Codes: P0733 Incorrect 3rd Gear Ratio

CIRCUIT DESCRIPTION:
The Transmission Control Module (TCM) uses input from the turbine speed sensor and output speed sensor to determine gear ratios. The TCM then compares the known gear ratio to the calculated gear ratio for the current range.

CONDITIONS FOR RUNNING THE DTC:
1. Output speed exceeds 200 rpm.
2. Third range is selected and attained.
3. DTC P0716, P0717, P0721, or P0722 is not active.

CONDITIONS FOR SETTING THE DTC:
DTC P0733 sets when the calculated third range ratio (steady state) differs from the known third range ratio.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P0733 is active, the following conditions will occur:
1. The transmission will fail to 4th range.
2. If the shift selector is moved to N (Neutral), the transmission will shift to N (Neutral).
3. If the shift selector is moved to R (Reverse), the transmission will shift to N (Neutral).
4. If the shift selector is returned to a forward range and the transmission is compromised by overspeeding or a direction change, the transmission will lock in N (Neutral).

DTC P0733 is stored in the TCM history.

The CHECK TRANS light illuminates.

The TCM freezes shift adapts (DNA).

The TCM inhibits TCC engagement.

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
A Scan Tool may be used to clear the code 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:
1. Incorrect ratio codes typically indicate mechanical problems with specific clutches, i.e. C1 and C3 for 3rd range.
2. An incorrect ratio code could indicate a hydraulically failed solenoid. Check the DTC information for the specific solenoid.
3. You may have to drive the vehicle to experience the fault. Clutch test mode can be used to check stall speed.
4. Incorrect TCM calibrations will cause this DTC to set. Verify that the proper TCM calibration is being used with the correct transmission family (there are different gear ratios for the 1000 and 2000 Product Families transmissions).

Allison 1000 & 2000 Gen 4 Fault Codes: P0734 Incorrect 4th Gear Ratio

CIRCUIT DESCRIPTION:
The Transmission Control Module (TCM) uses input from the turbine speed sensor and output speed sensor to determine gear ratios. The TCM then compares the known gear ratio to the calculated gear ratio for the current range.

CONDITIONS FOR RUNNING THE DTC:
1. Output speed exceeds 200 rpm.
2. Fourth range is selected and attained.
3. DTC P0716, P0717, P0721, or P0722 is not active.

CONDITIONS FOR SETTING THE DTC:
DTC P0734 sets when the calculated fourth range ratio (steady state) differs from the known fourth range ratio.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P0734 is active, the following conditions will occur:
1. The transmission will fail to 5th range.
2. If the shift selector is moved to N (Neutral), the transmission will shift to N (Neutral).
3. If the shift selector is moved to R (Reverse), the transmission will shift to R (Reverse) unless the transmission is compromised by a direction change; then the transmission will shift to N (Neutral).
4. If the shift selector is returned to a forward range and the transmission is compromised by overspeeding or a direction change, the transmission will lock in N (Neutral).

DTC P0734 is stored in the TCM history.

The CHECK TRANS light illuminates.

The TCM freezes shift adapts (DNA).

The TCM inhibits TCC engagement.

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
A Scan Tool may be used to clear the code 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:
1. Incorrect ratio codes typically indicate mechanical problems with specific clutches, i.e. C1 and C2 for 4th range.
2. An incorrect ratio code could indicate a hydraulically failed solenoid. Check the DTC information for the specific solenoid.
3. You may have to drive the vehicle to experience the fault. Clutch test mode can be used to check stall speed.

Allison 1000 & 2000 Gen 4 Fault Codes: P0735 Incorrect 5th Gear Ratio

CIRCUIT DESCRIPTION:
The Transmission Control Module (TCM) uses input from the turbine speed sensor and output speed sensor to determine gear ratios. The TCM then compares the known gear ratio to the calculated gear ratio for the current range.

CONDITIONS FOR RUNNING THE DTC:
1. Output speed exceeds 200 rpm.
2. Fifth range is selected and attained.
3. DTC P0716, P0717, P0721, or P0722 is not active.

CONDITIONS FOR SETTING THE DTC:
DTC P0735 sets when the calculated fifth range ratio (steady state) differs from the known fifth range ratio.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P0735 is active, the following conditions will occur:
1. The transmission will fail to 4th range.
2. If the shift selector is moved to N (Neutral), the transmission will shift to N (Neutral).
3. If the shift selector is moved to R (Reverse), the transmission will shift to R (Reverse) unless the transmission is compromised by a direction change; then the transmission will shift to N (Neutral).
4. If the shift selector is returned to a forward range and the transmission is compromised by overspeeding or a direction change, the transmission will lock in N (Neutral).

DTC P0735 is stored in the TCM history.

The CHECK TRANS light illuminates.

The TCM freezes shift adapts (DNA).

The TCM inhibits TCC engagement.

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
A Scan Tool may be used to clear the code 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:
1. Incorrect ratio codes typically indicate mechanical problems with specific clutches, i.e. C2 and C3 for 5th range.
2. An incorrect ratio code could indicate a hydraulically failed solenoid. Check the DTC information for the specific solenoid.
3. You may have to drive the vehicle to experience the fault. Clutch test mode can be used to check stall speed.
4. Incorrect TCM calibrations will cause this DTC to set. Verify that the proper TCM calibration is being used with the correct transmission family (there are different gear ratios for the 1000 and 2000 Product Families transmissions).

Allison 1000 & 2000 Gen 4 Fault Codes: P0736 Incorrect Reverse Ratio

CIRCUIT DESCRIPTION:
The Transmission Control Module (TCM) uses input from the turbine speed sensor and output speed sensor to determine gear ratios. The TCM then compares the known gear ratio to the calculated gear ratio for the current gear.

CONDITIONS FOR RUNNING THE DTC:
1. Output speed exceeds 200 rpm.
2. Reverse is selected and attained.
3. DTC P0716, P0717, P0721, or P0722 is not active.

CONDITIONS FOR SETTING THE DTC:
DTC P0736 sets when the calculated reverse range ratio (steady state) differs from the known reverse range ratio.

ACTION TAKEN WHEN THE DTC SETS:
1. When DTC P0736 is active, the transmission will lock in N (Neutral).
2. DTC P0736 is stored in the TCM history.
3. The CHECK TRANS light illuminates.
4. The TCM freezes shift adapts (DNA).
5. The TCM inhibits TCC engagement.

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
A Scan Tool may be used to clear the code 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:
1. Incorrect ratio codes typically indicate mechanical problems with specific clutches, i.e. C3 and CS for Reverse range.
2. An incorrect ratio code could indicate a hydraulically failed solenoid. Check the DTC information for the specific solenoid.
3. You may have to drive the vehicle to experience the fault. Clutch test mode can be used to check stall speed.

Allison 1000 & 2000 Gen 4 Fault Codes: P0741 Torque Converter Clutch System Stuck Off

CIRCUIT DESCRIPTION:
The Transmission Control Module (TCM) uses data from the engine speed sensor and the turbine speed sensor to calculate torque converter slip value. The TCM then compares this calculated slip value to a preset value in the TCM calibration.

CONDITIONS FOR RUNNING THE DTC:
1. DTC P0122, P0123, P0716, P0717, P0721, P0722, or P0743 (previously P1860) is not active.
2. The components are powered and ignition voltage is greater than 9V and less than 18V (12V TCM) or greater than 18V and less than 32V (24V TCM).
3. Engine speed is greater than 200 rpm for 5 seconds.
4. Transmission is in a valid forward range.
5. Throttle position is over 1 O percent but less than 90 percent.
6. Six seconds or more have expired since TCC was applied in a range.

CONDITIONS FOR SETTING THE DTC:
DTC P0741 sets when the TCM detects a torque converter clutch slip value greater than 80 rpm for more than 15 seconds, indicating no TCC apply.

ACTION TAKEN WHEN THE DTC SETS:
1. DTC P0741 is stored in the TCM history.
2. The CHECK TRANS light illuminates on the second occurrence.
3. The TCM freezes shift adapts (DNA).

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
A Scan Tool may be used to clear the code 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:
Residue or contamination may cause shift valves to stick intermittently.

Allison 1000 & 2000 Gen 4 Fault Codes: P0742 Torque Converter Clutch System Stuck On

CIRCUIT DESCRIPTION:
The Transmission Control Module (TCM) uses data from the engine speed sensor and the turbine speed sensor to calculate the torque converter slip value. The TCM then compares this calculated slip value to a preset value in the TCM calibration.

CONDITIONS FOR RUNNING THE DTC:
1. DTC P0122, P0123, P0716, P0717, P0721, P0722, P0726, P0727, or P0743 (previously P1860) is not active.
2. The components are powered and ignition voltage is greater than 9V and less than 18V (12V TCM) or greater than 18V and less than 32V (24V TCM).
3. Engine speed is greater than 200 rpm for 5 seconds.
4. Transmission is in a valid forward range.
5. The torque converter clutch is OFF.

CONDITIONS FOR SETTING THE DTC:
DTC P0742 sets when the conditions listed below are present and the TCM detects converter slip speed between -5 and -40 rpm for over 2 seconds.
1. Transmission output speed is 100 rpm or higher.
2. Engine throttle percentage is 15 percent or higher.
3. Engine torque is 130 N-m or higher.
4. Engine and turbine speed are under 5500 rpm.

ACTION TAKEN WHEN THE DTC SETS:
1. Illuminate CHECK TRANS light on second occurrence.
2. Response is calibration dependent.
3. If response is disabled, no action is performed.
4. If enabled, when DTC is set before or during a shift, response is a shift to neutral. If DTC is set after shifting is complete, transmission shifts to neutral or 1st range. While response is active, if the selector is moved to a forward range, transmission shifts to neutral or 1st range. If the selector is moved to reverse, the transmission shifts to neutral or reverse.

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
A Scan Tool may be used to clear the code 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:
This DTC sets when converter slip speed indicates the TCC is staying applied when it should be released for a period of time that is calibration dependent. This may indicate an internal failure of the TCC or a stuck or sticking TCC valve.