P0878

DTC P0878
Circuit Description
The pressure switch manifold (PSM) is a multiple-switch assembly made up of 3 normally open (N/O) pressure switches and 1 normally closed (N/C) pressure switch for reverse pressure. Fluid pressure is supplied to the pressure switch 4 (PS4) when the manual selector valve is in any position except REVERSE. When the manual selector valve is moved to REVERSE, pressure to PS4 is cut off, causing the switch to close.

DTC P0878 is a type B DTC.

DTC Descriptor
This diagnostic procedure supports the following DTC:

DTC P0878 Transmission Pressure Switch 4 Circuit High

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.
^ The transmission fluid temperature (TFT) is greater than 0°C (32°F).
^ DTC P0708 and P0877 is not active.

Conditions for Setting the DTC
DTC P0878 sets when P (PARK), N (NEUTRAL), or a forward range is selected and the PS4 state remains in the mechanically closed/electrically ON position for greater than 1.0 second.

Action Taken When the DTC Sets
^ The transmission control module (TCM) illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
^ The transmission will lock in NEUTRAL.
^ DTC P0878 is 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 could indicate a hydraulic leak path exhausting pressure from the reverse PS4.

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

Step 1 - Step 7:

Step 8 - Step 14: