Allison Automatic Transmission

ALLISON AUTOMATIC TRANSMISSION

DTC P0872
Circuit Description for Allison Automatic Transmission
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. The E pressure switch monitors E shift valve positioning and relays it to the transmission control module (TCM). When E pressure switch is in the open state, E shift valve should be in the unstroked position.

DTC P0872 is a type A DTC.

DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0872 Pressure Switch Solenoid E Circuit Low/Stuck Closed

Conditions for Running the DTC
^ The components are powered and ignition voltage is greater than 9.0 volts and less than 18 volts.
^ Engine speed is greater than 200 RPM and less than 7,500 RPM for 5 seconds.
^ E shift valve is commanded to the OFF, unstroked, position.

Conditions for Setting the DTC
DTC P0872 sets when E solenoid is commanded OFF and pressure switch E status remains ON for 2-20 seconds, depending on fluid temperature.

Action Taken When the DTC Sets
^ The TCM illuminates the malfunction indicator lamp (MIL).
^ The transmission fails to hydraulic default.
^ DTC P0872 will be stored in TCM history.
^ The TCM freezes shift adapts.
^ The TCM inhibits torque converter clutch (TCC) engagement.

Conditions for Clearing the DTC
A scan tool can clear the code from TCM history. The TCM automatically clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without failure.

Diagnostic Aids
^ Inspect the wiring for poor electrical connections at the TCM. Inspect for the following conditions:
- A bent terminal
- A backed-out terminal
- A damaged terminal
- Poor terminal tension
- A chafed wire
- 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 condition.
^ This DTC may indicate that E solenoid is mechanically defective.
^ When a P0872 and P0870 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.

Test Description








The numbers below refer to the step numbers on the diagnostic table.
5. This step tests the TCM response function.
7. This step tests the transmission wiring harness integrity.
8. This step tests and evaluates the internal wiring harness and inspects the PSM for a failed condition.
14. This step tests the engine wiring harness integrity.