Test Description

WARNING: This page is about a different variant/trim than selected.

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.

DTC P0878

Step	Action	Yes	No
Schematic Reference: Automatic Transmission Controls Schematics
1	Did you perform the Diagnostic System Check - Vehicle?	Go to Step 2	Go to Diagnostic System Check - Vehicle
2	Measure the transmission fluid level. Refer to Transmission Fluid Checking Procedure . Is the transmission fluid level correct?	Go to Step 3	Go to Transmission Fluid Checking Procedure
3	Measure line pressure. Refer to Line Pressure Check Procedure . Is the line pressure within the specified value?	Go to Step 4	Go to Symptoms - Automatic Transmission
4	Install the scan tool. Turn ON the ignition, with the engine OFF. IMPORTANT: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records for reference. The Clear Info function will erase the data. Record the DTC Freeze Frame and Failure Records. Clear the DTC. Start the engine. Using the scan tool, monitor PS4 status. Does the scan tool indicate PS4 status is OFF?	Go to Diagnostic Aids	Go to Step 5
5	Turn the ignition OFF. Disconnect the 80-way connector at the TCM. Install the J 39700 breakout box, the J-47275 breakout box adapter and the J 47275-1 magnetic overlay. See Special Tools . Turn ON the ignition, with the engine OFF. Connect terminal 77 to ground. Does the scan tool indicate PS4 status is ON when grounded and OFF when open?	Go to Step 6	Go to Step 12
6	Turn the ignition OFF. Disconnect the AT inline 20-way connector. Additional DTCs may set. Install the J 44152 jumper harness (20 pins) on the engine side of the AT inline 20-way connector. Turn ON the ignition, with the engine OFF. Using the J 35616 GM terminal test kit and a fused jumper wire, connect terminal K of the J 44152 to ground. Refer to Automatic Transmission Inline Harness Connector End View . Does the scan tool indicate PS4 status is ON when grounded and OFF when open?	Go to Step 7	Go to Step 11
7	Connect the AT inline 20-way connector. Remove the transmission oil pan. Refer to Oil Pan Replacement . Disconnect the AT internal wiring harness from the PSM and ground terminal D. Does the scan tool indicate PS4 status is ON when grounded and OFF when open?	Go to Step 8	Go to Step 10
8	Remove the PSM from the control valve body and leave the internal harness connected. Refer to Pressure Switch Manifold Replacement . Provide a ground connection for the PSM to either the control valve body or the transmission main case. Using the eraser end of a pencil, push gently on pressure switch R membrane. Does the scan tool indicate PS4 status is ON when grounded and OFF when open?	Go to Step 9	Go to Diagnostic Aids
9	Replace the PSM. Refer to Pressure Switch Manifold Replacement . Did you complete the replacement?	Go to Step 13	-
10	Replace the internal wiring harness. Refer to Wiring Harness Replacement . Did you complete the replacement?	Go to Step 13	-
11	Replace the AT internal wiring harness. Refer to Wiring Harness Replacement . Did you complete the replacement?	Go to Step 13	-
12	IMPORTANT: In most cases, the TCM is not at fault. Investigate thoroughly before replacing the TCM. Replace the TCM. Refer to Control Module References for replacement, setup and programming.Did you complete the replacement?	Go to Step 13	-
13	Perform the following procedure in order to verify the repair: Clear the DTC. Start the engine. Using the scan tool, monitor PS4 status. Select Specific DTC. Enter DTC P0878. Has the test run and passed?	Go to Step 14	Go to Step 2
14	With the scan tool, observe the stored information, capture info and DTC info. Does the scan tool display and DTCs that you have not diagnosed?	Go to Diagnostic Trouble Code (DTC) List - Vehicle	System OK