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Home >> GMC >> 2006 >> Yukon Denali >> Repair and Diagnosis >> External Pages >> Different car >> Section 792 (Automatic Transmission - 4L80-E/4L85-E - DTC P0218 To DTC P2771) >> DTC P0748 >> Test Description

Test Description

WARNING: This page is about a different car, the 2006 GMC Yukon XL, 2006 Chevrolet Suburban, and 2006 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.

The numbers below refer to the step numbers on the diagnostic table.

  1. 2:  This step tests the ability of the PCM to command the PC solenoid valve.
  2. 3:  This step tests the PC solenoid valve and the automatic transmission (AT) wiring harness assembly for correct resistance.
  3. 6:  This step tests the PC solenoid valve and the internal wiring harness for a short to ground.
  4. 9:  This step tests the entire PC solenoid valve circuit up to the PCM for continuity.
  5. 10:  This step tests for a short to ground in the PC solenoid valve high control, solenoid A, circuit and the PC solenoid valve low control, solenoid A, circuit, of the engine harness.
DTC P0748

Step Action Value Yes No
1 Did you perform the Diagnostic System Check - Vehicle? - Go to Step 2  Go to Diagnostic System Check - Vehicle
2 
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
    3. IMPORTANT: Before clearing the DTCs, use the scan tool in order to record the Failure Records. Using the Clear Info Function erases the Failure Records from the PCM.
  3. Record the Failure Records.
  4. Clear the DTCs.
  5. With the transmission in PARK, start the engine.
  6. Using the Transmission Output Control Function on the scan tool, apply 0.1-1.0 amp while observing the PC Ref. current and the PC Act. current. Refer to Line Pressure .
Does the PC Sol. Actual current differ from the PC Sol. Ref. current greater than the specified amount?		 0.16 amp Go to Step 3  Go to Testing for Intermittent Conditions and Poor Connections
3 
  1. Turn OFF the ignition.
  2. Disconnect the transmission 20-way connector. Additional DTCs may set.
  3. Install the J 44152  jumper harness (20 pins) on the transmission side of the 20-way connector.
  4. Using the DMM and the J 35616  GM terminal test kit, measure the resistance between terminal C and D. See Special Tools .
Does the resistance measure within the specified value?		 3-7 Ω Go to Step 7  Go to Step 4 
4 Is the resistance greater than the specified value? 7 Ω Go to Step 5  Go to Step 6 
5
  1. Test the high control circuit of the PC solenoid valve for an open between the AT inline 20-way connector and the PC solenoid valve.
  2. Test the low control circuit of the PC solenoid valve for an open between the AT inline 20-way connector and the PC solenoid valve.
Refer to Testing for Continuity .Did you find the condition?		 - Go to Step 15  Go to Step 14 
6  Test the high control circuit and the low control circuit of the PC solenoid valve for a short together between the AT inline 20-way connector and the PC solenoid valve. Refer to Circuit Testing .
Did you find the condition?		 - Go to Step 15  Go to Step 14 
7
  1. Test the high control circuit of the PC solenoid valve for a short to the transmission case between the AT inline 20-way connector and the PC solenoid valve.
  2. Test the high control circuit of the PC solenoid valve for a short to other voltages and ground circuits in the transmission harness. Test from terminal C to all other terminals in the transmission 20-way connector.
Refer to Automatic Transmission Inline 20-Way Connector End View and Testing for Short to Ground .Did you find the condition?		 - Go to Step 15  Go to Step 8 
8
  1. Test the low control circuit of the PC solenoid valve for a short to the transmission case between the AT inline 20-way connector and the PC solenoid valve.
  2. Test the low control circuit of the PC solenoid valve for a short to other voltages and ground circuits in the transmission harness. Test from terminal D to all other terminals in the transmission 20-way connector.
Refer to Automatic Transmission Inline 20-Way Connector End View and Testing for Short to Ground .Did you find the condition?		 - Go to Step 15  Go to Step 9 
9 
  1. Disconnect the J 44152  from the transmission side of the 20-way connector.
  2. Connect the 20-way connector.
  3. Disconnect the PCM connector C2.
  4. Using the DMM, measure the resistance of the PC solenoid circuit from the PCM harness connector terminal C2-6 to C2-8.
Does the resistance measure within the specified range?		 3-7 Ω Go to Step 13  Go to Step 10 
10  Does the resistance measure greater than the specified value? 7 Ω Go to Step 11  Go to Step 12 
11
  1. Test the high control circuit of the PC solenoid valve for an open between the PCM and the AT inline 20-way connector.
  2. Test the low control circuit of the PC solenoid valve for an open between the PCM and the AT inline 20-way connector.
Refer to Testing for Continuity and Wiring Repairs .Did you find and correct the condition?		 - Go to Step 17  -
12 Test the high control circuit and the low control circuit of the PC solenoid valve for a short together between the PCM and the AT inline 20-way connector. Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 - Go to Step 17  -
13
  1. Test the high control circuit of the PC solenoid valve for a short to ground or short to voltage between the PCM and the AT inline 20-way connector.
  2. Test the low control circuit of the PC solenoid valve for a short to ground or short to voltage between the PCM and the AT inline 20-way connector.
Refer to Testing for Short to Ground and Wiring Repairs .Did you find and correct the condition?		 - Go to Step 17  Go to Step 16 
14 Replace the pressure control solenoid valve. Refer to Valve Body and Pressure Switch Replacement .
Did you complete the replacement?		 - Go to Step 17  -
15 Replace the automatic transmission wiring harness assembly. Refer to Valve Body and Pressure Switch Replacement .
Did you complete the replacement?		 - Go to Step 17  -
16 Replace the PCM. Refer to Control Module References for replacement, setup, and programming.
Did you complete the replacement?		 - Go to Step 17  -
17 Perform the following procedure in order to verify the repair:
  1. Select DTC.
  2. Select Clear Info.
  3. Start the engine.
  4. The PC Duty Cycle is 2-95%.
  5. Select Specific DTC.
  6. Enter DTC P0748.

Has the test run and passed?		 - Go to Step 18  Go to Step 2 
18 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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