Allison

CIRCUIT DESCRIPTION:
The 4WD low signal circuit notifies the TCM that the vehicle is in 4WD low range. When this function is enabled, the TCM adjusts specific shift calibration values to accommodate for changes in vehicle performance which result from the shift to low range at the transfer case.

Wires used for this function can vary depending on the vocational package used, therefore it is important to check the diagnostic tool and/or the calibration summary to see which wires are implemented. Wires 102 and 103 (signal ground return) should be used in part time high N/V input function (CC1) applications along with either wire 122 or 101, depending on the vocational package used. Full time high N/V input function (CC2) only uses wire 103 wired directly to wire 122, leaving wire 102 open.

ACTION TAKEN WHEN THE DTC SETS:
1. DTC P0837 is stored in the TCM memory.
2. The CHECK TRANS light illuminates.
3. The TCM inhibits GPI function.

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 the DTC recurring.

DIAGNOSTIC AIDS:
Switch Status Displayed in The Diagnostic Tool:
Transfer Case Range: Low
Input-High NN Switch State 1 (Wire 122 or 101): On (closed)
Input-High NN Switch State 2 (Wire 102): On (open)

Transfer Case Range: Neutral
Input-High NN Switch State 1 (Wire 122 or 101): Off (open)
Input-High NN Switch State 2 (Wire 102): On (closed)

Transfer Case Range: High
Input-High NN Switch State 1 (Wire 122 or 101): Off (open)
Input-High NN Switch State 2 (Wire 102): On (closed)

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.

When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.

You may have to drive the vehicle in order to experience a fault. Use the data obtained from failure records to determine transmission range and/or certain vehicle operating variables such as temperature, run time etc. This data can be useful in reproducing the failure mode when the DTC was set.

Check the diagnostic tool or calibration summary for specific input wire numbers.

Multiple inactive pressure switch DTCs may be due to a plugged control main filter.

CIRCUIT DESCRIPTION:
The Pressure Switch Manifold (PSM) is a multiple-switch assembly made up of three Normally Open (N/O) and one Normally Closed (N/C) pressure switches. PS1 monitors SV1 positioning and relays it to the TCM. DTC P0843 sets during steady state (all shift valves are commanded to their proper state and a valid range is attained) operation when SV1 is in the stroked state (commanded ON) and PS1 status is detected as destroked (Exhausted/OFF). The intent of this DTC is to detect an open condition in the pressure switch wiring circuit or the pressure switch. This diagnostic test is designed to compare the commanded shift valve position to the pressure switch feedback. Pending failure occurs when the switch indicates stroked for a calibrated time (if main pressure dropout is detected this time increases). In response to pending failure, SS1 is commanded to stroke and unstroke (retry logic). If the PS1 still indicates stroked, a DTC is set.

There is one of three possible failures that could be present:
1. Electrical malfunction – sets P0843
2. Mechanical malfunction – also sets P0751
3. Intermittent malfunction – retry logic attempts to command SS1

ACTION TAKEN WHEN THE DTC SETS:
When DTC P0843 is active, the following conditions occurs:
1. If the failure occurs while in a forward range a shift to 1st, 3rd, or 5th range is made.
2. While diagnostic response is active, if shift selector is moved to N (Neutral), transmission shifts to neutral; if the shift selector is moved to R (Reverse), transmission shifts to reverse. If the shift selector is moved to D (Drive) range or R (Reverse) and transmission is compromised by overspeeding or direction change, the transmission shifts to neutral.
3. The CHECK TRANS light illuminates (non-OBD II strategy).
4. DTC is stored in TCM history.
5. The TCM forces Variable Modulated Main off.
6. The TCM inhibits TCC engagement.
7. 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 the DTC recurring.

DIAGNOSTIC AIDS:
The following procedures are not documented in any OEM procedures or in any OEM Troubleshooting or Service information and should not be used as a method to diagnose any transmission DTCs, function, or shift quality concern:

1. Back-probing any connections used for transmission features or functions may damage and/or unlock terminals from the back-probed connector creating permanent or intermittent shorts and/or open circuits. If possible, use the J-39700 Breakout Box, the appropriate harness adapters, and appropriate magnetic overlays to troubleshoot the vehicle.

2. Load-testing any transmission-related circuits with any other electrical devices such as vehicle lamps or relays, especially with the TCM connected to the harness. Use J-39700 Breakout Box and appropriate harnesses with the diagnostic tool to monitor the circuit performance in question unless otherwise specified in the various Troubleshooting information.

3. Piercing a wire to check for voltages, shorts-to-grounds or other wires anywhere in the circuit but especially at the TCM. This creates a leak path for moisture and damages the wire and insulation.

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.

When only P0843 sets look for an intermittent open condition at the pressure switch circuit. This DTC sets when the condition is present more than 3 occurrences during the current drive cycle (refer to DIAGNOSING INTERMITTENT DTCs information).

When P0843 and P0751 are set in combination, the TCM logic re-attempted to command the shift solenoid on. A circuit or pressure switch concern is still present or continuous and not intermittent in nature.

When P0751 and P0843 are set in combination this may indicate a continuous open circuit condition is present at the pressure switch circuit or the shift valve is stuck in the destroked state (refer to TROUBLESHOOTING PROCESS information).

When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change. It may be necessary to check for shorting-to-ground at individual wires within a harness to isolate an intermittent condition (refer to WIRE CHECK and DIAGNOSING INTERMITTENT DTCs information).

You may have to drive the vehicle in order to experience a fault. Use the data obtained from failure records to determine transmission range and/or certain vehicle operating variables such as temperature, run time etc. This data can be useful in reproducing failures mode where DTC was set.

Multiple inactive pressure switch DTCs may be due to a plugged control main filter.

CIRCUIT DESCRIPTION:
The Pressure Switch Manifold (PSM) is a multiple-switch assembly made up of three Normally Open (N/O) and one Normally Closed (N/C) pressure switches. PS2 monitors SV2 positioning and relays it to the TCM. DTC P0847 sets during steady state (all shift valves are commanded to their proper state and a valid range is attained) operation when SV2 is in the stroked state (commanded OFF) and PS2 status is detected as stroked (Pressurized/ON). The intent of this DTC is to detect shorts-to-ground in the pressure switch wiring circuit or the pressure switch. This diagnostic test is designed to compare the commanded shift valve position to the pressure switch feedback. Pending failure occurs when the switch indicates stroked for a calibrated time (if main pressure dropout is detected this time increases). In response to pending failure, SS2 is commanded to stroke and unstroke (retry logic). If the PS2 still indicates stroked, a DTC is set.

There is one of three possible failures that could be present:
1. Electrical malfunction – sets P0847
2. Mechanical malfunction – also sets P0976
3. Intermittent malfunction – retry logic attempts to command SS2 up to 2 times

ACTION TAKEN WHEN THE DTC SETS:
When DTC P0847 is active, the following conditions occurs:
1. If the failure occurs while in a forward range a shift to 1st, 3rd, or 5th range is made.
2. While diagnostic response is active, if shift selector is moved to N (Neutral), transmission shifts to neutral; if the shift selector is moved to R (Reverse), transmission shifts to reverse. If the shift selector is moved to D (Drive) range or R (Reverse) and transmission is compromised by overspeeding or direction change, transmission shifts to neutral.
3. The CHECK TRANS light illuminates (non-OBD II strategy).
4. DTC is stored in TCM history.
5. The TCM forces Variable Modulated Main off.
6. The TCM inhibits TCC engagement.
7. 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 the DTC recurring.

DIAGNOSTIC AIDS:
The following procedures are not documented in any OEM procedures or in any OEM Troubleshooting or Service information and should not be used as a method to diagnose any transmission DTCs, function, or shift quality concern:

1. Back-probing any connections used for transmission features or functions may damage and/or unlock terminals from the back-probed connector creating permanent or intermittent shorts and/or open circuits. If possible, use the J-39700 Breakout Box, the appropriate harness adapters, and appropriate magnetic overlays to troubleshoot the vehicle.

2. Load-testing any transmission-related circuits with any other electrical devices such as vehicle lamps or relays, especially with the TCM connected to the harness. Use J-39700 Breakout Box and appropriate harnesses with the diagnostic tool to monitor the circuit performance in question unless otherwise specified in the various Troubleshooting information.

3. Piercing a wire to check for voltages, shorts-to-grounds or other wires anywhere in the circuit but especially at the TCM. This creates a leak path for moisture and damages the wire and insulation.

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.

When only P0847 sets look for an intermittent short-to-ground at the pressure switch circuit. This DTC sets when the condition is present for more than 3 occurrences during the current drive cycle (refer to DIAGNOSING INTERMITTENT DTCs information).

When P0847 and P0757 are set in combination, the TCM logic re-attempted to command the shift solenoid on. A circuit or pressure switch concern is still present or continuous and not intermittent in nature.

When P0757 and P0847 are set in combination this may indicate a short-to-ground is present at the pressure switch circuit or the shift valve is stuck in the stroked state (refer to TROUBLESHOOTING PROCESS information).

When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change. It may be necessary to check for shorting-to-ground at individual wires within a harness to isolate an intermittent condition (refer to WIRE CHECK and DIAGNOSING INTERMITTENT DTCs information).

You may have to drive the vehicle in order to experience a fault. Use the data obtained from failure records to determine transmission range and/or certain vehicle operating variables such as temperature, run time etc. This data can be useful in reproducing failures mode where DTC was set.

Multiple inactive pressure switch DTCs may be due to a plugged control main filter.

CIRCUIT DESCRIPTION:
The Pressure Switch Manifold (PSM) is a multiple-switch assembly made up of three Normally Open (N/O) and one Normally Closed (N/C) pressure switches. PS3 monitors SV3 positioning and relays it to the TCM. DTC P0872 sets during steady state (all shift valves are commanded to their proper state and a valid range is attained) operation when SV3 is in the destroked state (commanded OFF) and PS3 status is detected as destroked (Pressurized/ON).

The intent of this DTC is to detect shorts-to-ground in the pressure switch wiring circuit or the pressure switch. This diagnostic test is designed to compare the commanded shift valve position to the pressure switch feedback. Pending failure occurs when the switch indicates stroked for a calibrated time (if main pressure dropout is detected this time increases). In response to pending failure, SS3 is commanded to stroke and unstroke (retry logic). If the PS3 still indicates stroked, a DTC is set.

There is one of three possible failures that could be present:
1. Electrical malfunction – sets P0872.
2. Mechanical malfunction – also sets P0762.
3. Intermittent malfunction – retry logic attempts to command SS3 up to 2 times.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P0872 is active, the following conditions occurs:
1. If the failure occurs while in a forward range a shift to 1st, 3rd, or 5th range is made.
2. While diagnostic response is active, if the shift selector is moved to N (Neutral), transmission shifts to neutral; if the shift selector is moved to R (Reverse), transmission shifts to reverse. If the shift selector is moved to D (Drive) range or R (Reverse) and transmission is compromised by overspeeding or direction change, transmission shifts to neutral.
3. The CHECK TRANS light illuminates (non-OBD II strategy).
4. DTC is stored in TCM history.
5. The TCM forces Variable Modulated Main off.
6. The TCM inhibits TCC engagement.
7. 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 the DTC recurring.

DIAGNOSTIC AIDS:
The following procedures are not documented in any OEM procedures or in any OEM Troubleshooting or Service information and should not be used as a method to diagnose any transmission DTCs, function, or shift quality concern:

1. Back-probing any connections used for transmission features or functions may damage and/or unlock terminals from the back-probed connector creating permanent or intermittent shorts and/or open circuits. If possible, use the J-39700 Breakout Box, the appropriate harness adapters, and appropriate magnetic overlays to troubleshoot the vehicle.

2. Load-testing any transmission-related circuits with any other electrical devices such as vehicle lamps or relays, especially with the TCM connected to the harness. Use J-39700 Breakout Box and appropriate harnesses with the diagnostic tool to monitor the circuit performance in question unless otherwise specified in the various Troubleshooting information.

3. Piercing a wire to check for voltages, shorts-to-grounds or other wires anywhere in the circuit but especially at the TCM. This creates a leak path for moisture and damages the wire and insulation.

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.

When only P0872 sets look for an intermittent short-to ground at the pressure switch circuit. This DTC sets when the condition is present for more than 3 occurrences during the current drive cycle (refer to DIAGNOSING INTERMITTENT DTCs information).

When P0872 and P0762 are set in combination, the TCM logic re-attempted to command the shift solenoid on. A circuit or pressure switch concern is still present or continuous and not intermittent in nature.

When P0762 and P0872 are set in combination this may indicate a short-to-ground is present at the pressure switch circuit or the shift valve is stuck in the stroked state (refer to TROUBLESHOOTING PROCESS information).

When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change. It may be necessary to check for shorting-to-ground at individual wires within a harness to isolate an intermittent condition (refer to WIRE CHECK and DIAGNOSING INTERMITTENT DTCs information).

You may have to drive the vehicle in order to experience a fault. Use the data obtained from failure records to determine transmission range and/or certain vehicle operating variables such as temperature, run time etc. This data can be useful in reproducing failures mode where DTC was set.

Multiple inactive pressure switch DTCs may be due to a plugged control main filter.

CIRCUIT DESCRIPTION:
The Pressure Switch Manifold (PSM) is a multiple-switch assembly made up of three Normally Open (N/O) and one Normally Closed (N/C) pressure switches. PS3 monitors SV3 positioning and relays it to the TCM. DTC P0873 sets during steady state (all shift valves are commanded to their proper state and a valid range is attained) operation when SV3 is in the stroked state (commanded ON) and PS3 status is detected as destroked (Exhausted/OFF).

The intent of this DTC is to detect an open condition in the pressure switch wiring circuit or the pressure switch. This diagnostic test is designed to compare the commanded shift valve position to the pressure switch feedback. Pending failure occurs when the switch indicates stroked for a calibrated time (if main pressure dropout is detected this time increases). In response to pending failure, SS3 is commanded to stroke and unstroke (retry logic). If the PS3 still indicates stroked, a DTC is set.

There is one of three possible failures that could be present:
1. Electrical malfunction – sets P0873
2. Mechanical malfunction – also sets P0761
3. Intermittent malfunction – retry logic attempts to command SS3 up to 2 times

ACTION TAKEN WHEN THE DTC SETS:
When DTC P0873 is active, the following conditions occurs:
1. If the failure occurs while in a forward range a shift to 1st, 3rd, or 5th range is made.
2. While diagnostic response is active, if the shift selector is moved to N (Neutral), transmission shifts to neutral; if the shift selector is moved to R (Reverse), transmission shifts to reverse. If the shift selector is moved to D (Drive) range or R (Reverse) and transmission is compromised by overspeeding or direction change, transmission shifts to neutral.
3. The CHECK TRANS light illuminates (non-OBD II strategy).
4. DTC is stored in TCM history.
5. The TCM forces Variable Modulated Main off.
6. The TCM inhibits TCC engagement.
7. 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 the DTC recurring.

DIAGNOSTIC AIDS:
The following procedures are not documented in any OEM procedures or in any OEM Troubleshooting or Service information and should not be used as a method to diagnose any transmission DTCs, function, or shift quality concern:

1. Back-probing any connections used for transmission features or functions may damage and/or unlock terminals from the back-probed connector creating permanent or intermittent shorts and/or open circuits. If possible, use the J-39700 Breakout Box, the appropriate harness adapters, and appropriate magnetic overlays to troubleshoot the vehicle.

2. Load-testing any transmission-related circuits with any other electrical devices such as vehicle lamps or relays, especially with the TCM connected to the harness. Use J-39700 Breakout Box and appropriate harnesses with the diagnostic tool to monitor the circuit performance in question unless otherwise specified in the various Troubleshooting information.

3. Piercing a wire to check for voltages, shorts-to-grounds or other wires anywhere in the circuit but especially at the TCM. This creates a leak path for moisture and damages the wire and insulation.

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.

When only P0873 sets look for an intermittent open condition at the pressure switch circuit. This DTC sets when the condition is present for more than 3 occurrences during the current drive cycle (refer to DIAGNOSING INTERMITTENT DTCs information).

When P0873 and P0761 are set in combination, the TCM logic re-attempted to command the shift solenoid on. A circuit or pressure switch concern is still present or continuous and not intermittent in nature.

When P0761 and P0873 are set in combination this may indicate a continuous open circuit condition at the pressure switch circuit or the shift valve is stuck in the destroked state (refer to TROUBLESHOOTING PROCESS information).

When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change. It may be necessary to check for shorting-to-ground at individual wires within a harness to isolate an intermittent condition (refer to WIRE CHECK and DIAGNOSING INTERMITTENT DTCs information).

You may have to drive the vehicle in order to experience a fault. Use the data obtained from failure records to determine transmission range and/or certain vehicle operating variables such as temperature, run time etc. This data can be useful in reproducing failures mode where DTC was set.

Multiple inactive pressure switch DTCs may be due to a plugged control main filter.

CIRCUIT DESCRIPTION:
The Pressure Switch Manifold (PSM) is a multiple-switch assembly made up of three Normally Open (N/O) and one Normally Closed (N/C) pressure switches. Fluid pressure is supplied to PS4, holding it open when the manual selector valve is in any position except reverse. When the manual selector valve is moved to reverse, pressure to the PS4 is cut off, allowing the switch to close. DTC P0877 sets when P (Park), N (Neutral), or a forward range is selected and the PS4 state remains in the Exhausted/ON position for a period of time that is calibration dependent.

ACTIONS TAKEN WHEN DTC IS SET
When DTC P0877 is active, the following conditions occurs:
1. Calibration dependent – Either lock to neutral or transmission shifts to 3rd or 5th range.
2. While diagnostic response is active, if the shift selector is moved to N (Neutral), transmission shifts to neutral; if the shift selector is moved to R (Reverse), transmission shifts to reverse. If the shift selector is moved to D (Drive) range or R (Reserve) and transmission is compromised by overspeeding or direction change, transmission shifts to neutral. If output speed fault or Internal Mode Switch (IMS) fault is present when this test fails, then hydraulic default is implemented.
3. The CHECK TRANS light illuminates (non-OBD II strategy).
4. DTC is stored in TCM history.
5. The TCM forces Variable Modulated Main off.
6. The TCM inhibits TCC engagement.
7. 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 the DTC recurring.

DIAGNOSTIC S AIDS
The following procedures are not documented in any OEM procedures or in any OEM Troubleshooting or Service information and should not be used as a method to diagnose any transmission DTCs, function, or shift quality concern:

1. Back-probing any connections used for transmission features or functions may damage and/or unlock terminals from the back-probed connector creating permanent or intermittent shorts and/or open circuits. If possible, use the J-39700 Breakout Box, the appropriate harness adapters, and appropriate magnetic overlays to troubleshoot the vehicle.

2. Load-testing any transmission-related circuits with any other electrical devices such as vehicle lamps or relays, especially with the TCM connected to the harness. Use J-3700 Breakout Box and appropriate harnesses with the diagnostic tool to monitor the circuit performance in question unless otherwise specified in the various Troubleshooting information.

3. Piercing a wire to check for voltages, shorts-to-grounds or other wires anywhere in the circuit but especially at the TCM. This creates a leak path for moisture and damages the wire and insulation.

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.

This DTC could indicate a hydraulic leak path exhausting pressure from the reverse pressure switch (refer to HYDRAULIC SCHEMATICS information).

If P0877 is shown in failure records as being logged first on the failure list followed by P0762 combined with P0708, these DTCs may indicate an IMS failure. Inspect the shift linkage carefully for proper adjustment.

When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change. It may be necessary to check for shorting-to-ground at individual wires within a harness to isolate an intermittent condition (refer to WIRE CHECK and DIAGNOSING INTERMITTENT DTCs information).

You may have to drive the vehicle in order to experience a fault. Use the data obtained from failure records to determine transmission range and/or certain vehicle operating variables such as temperature, run time etc. This data can be useful in reproducing failures mode where the DTC was set.