LEMON Manuals: Even more car manuals for everyone
Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1072 (Automatic Transmission - ALLISON, Diagnosis (DTC P0736 To DTC P0872)) >> Diagnosis >> DTC P0748 >> Test Description

Test Description

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. 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. 3:  This step tests ignition voltage to the TCM.
  2. 4:  This step tests the supply voltage to the TCM.
  3. 5:  This step tests the resistance value of the external harness and solenoid.
  4. 6:  This step tests the resistance value of the solenoid, and tests the internal wiring harness for opens or shorts.
  5. 7:  This step tests the resistance value of the solenoid.
DTC P0748

Step Action Value Yes No
Schematic Reference: Automatic Transmission Controls Schematics
1 Did you perform the Diagnostic System Check - Automatic Transmission? - Go to Step 2  Go to Diagnostic System Check - Automatic Transmission
2
  1. Install the scan tool.
  2. Start the engine.
    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. Using the scan tool, measure ignition voltage.
Is the voltage within the specified range?		 9-18 V Go to Step 3  Go to DTC P0562 for low voltage or DTC P0563 for high voltage
3 
  1. Turn the ignition OFF.
  2. Disconnect the C1 connector (GRAY) at the TCM.
  3. Install the J 39700  breakout box and the J 43799  breakout box adapter.
  4. Turn ON the ignition, with the engine OFF.
  5. Using a DMM, measure voltage at connector C1 terminals 2, 4, and 3 to a known good ground.
Is the voltage within specified range?		 B+ Go to Step 4  Go to Diagnostic Aids
4 
  1. Turn the ignition OFF.
  2. Disconnect the C2 connector (RED) at the TCM.
  3. Install the J 39700  breakout box and the J 43799  breakout box adapter.
  4. Using a DMM, measure voltage between connector C2 terminal 22 and terminal 23.
  5. Turn ON the ignition, with the engine OFF.
  6. Using the scan tool, command PC solenoid A ON.
Is the voltage within the range specified when PC solenoid A is commanded ON?		 7-7.5 V Go to Step 5  Go to Step 11 
5 
  1. Turn the ignition OFF.
  2. Using a DMM measure the resistance between connector C2 terminal 22 and terminal 23.
Is the resistance within the specified range?		 5.5 ohm @ 20°C (68°F) Go to Diagnostic Aids Go to Step 6 
6 
  1. Connect the C2 connector (RED) to the TCM.
  2. Disconnect the transmission 20-way connector.
  3. Using a DMM, measure the resistance between terminals L and M of the transmission side 20-way connector.
Is resistance within the specified range?		 5.5 ohm @ 20°C (68°F) Go to Step 9  Go to Step 7 
7 
  1. Remove the oil pan. Refer to Oil Pan Replacement .
  2. Remove the internal wiring harness at the A solenoid connector.
  3. Using the DMM, measure the resistance of PC solenoid A.
Is the solenoid resistance within the specified valve?		 5.5 ohm @ 20°C (68°F) Go to Step 8  Go to Step 10 
8 Replace the internal wiring harness. Refer to Wiring Harness Replacement .
Did you complete the replacement?		 - Go to Step 12  -
9 Inspect the engine wiring harness circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct a condition?		 - Go to Step 12  -
10 Replace PC solenoid A. Refer to Control Valve Solenoid Replacement (Solenoid A, B) or Control Valve Solenoid Replacement (Solenoid C, D, E, F, G) .
Did you complete the replacement?		 - Go to Step 12  -
11
IMPORTANT: In most cases, the TCM is not at fault. Investigate thoroughly before replacing the TCM.
Replace the TCM. Refer to Transmission Control Module (TCM) Replacement .Did you complete the replacement?		 - Go to Step 12  -
12 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 P0748.

Has the test run and passed?		 - System OK Go to Step 1 
scientia non olet · About LEMON Manuals