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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 939 (Automatic Transmission - ALLISON - DTC P0877 To DTC P2670) >> DTC P0978 >> Test Description

Test Description

WARNING: This page is about a different car, the 2007 GMC Sierra and 2007 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.

The number below refers to the step number on the diagnostic table.

  1. 3:  This step tests the command signal from the TCM.
DTC P0978

Step Action Value 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
  1. Install the scan tool.
  2. Turn ON the ignition, with the engine OFF.
    3. 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.
  3. Record the DTC Freeze Frame and Failure Records.
  4. Clear the DTC.
  5. Test drive the vehicle while collecting a snapshot and verify that the code becomes active during the drive.
Did the code become active?		 Code Active Go to Step 3  Go to Testing for Intermittent Conditions and Poor Connections
3 
  1. Turn the ignition OFF.
  2. Disconnect the 80-way connector at the TCM.
  3. Install the J 39700  breakout box, the J-47275  breakout box adapter and the J 47275-1 magnetic overlay.
  4. Turn ON the ignition, with the engine OFF.
  5. Using the DMM, measure the voltage between connector terminal 51 and ground.
  6. Using the scan tool, command SS3 to OFF.
Is the voltage within the specified value when SS3 is commanded OFF?		 B+ Go to Step 4  Go to Step 5 
4 Command the solenoid ON.
Did you get less than 5 volts with the solenoid commanded ON?		 < 5.0 volts Go to Testing for Intermittent Conditions and Poor Connections Go to Step 10 
5
  1. Disconnect the AT inline 20-way connector.
  2. Install the J 44152  jumper harness (20 pins) on the transmission side of the AT inline 20-way connector.
  3. Using the DMM and the J 35616  GM terminal test kit, measure the resistance at terminal C and N of the J 44152  . Refer to Automatic Transmission Inline Harness Connector End View .
Is the resistance within the specified value?		 22.0 Ω at 20°C (68°F) Go to Step 7  Go to Step 6 
6
  1. Remove the transmission oil pan. Refer to Oil Pan Replacement .
  2. Remove the AT internal wiring harness at the SS3 connector.
  3. Using the DMM, measure the resistance of SS3.
Is the solenoid resistance within the specified value?		 22.0 Ω at 20°C (68°F) Go to Step 8  Go to Step 9 
7 Test the SS3 circuit between the TCM and the AT inline 20-way connector for an open condition. Refer to Testing for Continuity .
Did you find and correct the condition?		 - Go to Step 11  -
8 Replace the AT internal wiring harness. Refer to Wiring Harness Replacement .
Did you complete the replacement?		 - Go to Step 11  -
9 Replace the SS3. Refer to Control Valve Solenoid Replacement (PCS1 and PCS2) or Control Valve Solenoid Replacement (SS1, SS2, SS3, TCC, and MAIN MOD) .
Did you complete the replacement?		 - Go to Step 11  -
10
IMPORTANT: In most cases, the TCM is not at fault. Investigate thoroughly before replacing the TCM. Swap the TCM with a known good TCM to confirm diagnosis.
Replace the TCM. Refer to Control Module References for replacement, setup and programming.Did you complete the replacement?		 - Go to Step 11  -
11 Perform the following procedure in order to verify the repair:
  1. Clear the DTC.
  2. Drive the vehicle under normal operating conditions.
  3. Select Specific DTC.
  4. Enter DTC P0978.

Has the test run and passed?		 - Go to Step 12  Go to Step 2 
12 With the scan tool, observe the stored information, capture info and DTC info.
Does the scan tool display any DTCs that you have not diagnosed?		 - Go to Diagnostic Trouble Code (DTC) List - Vehicle System OK
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