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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1077 (Automatic Transmission - ALLISON, Diagnosis (DTC P0873 To DTC P2810)) >> Diagnosis >> DTC P1688 >> Test Description

Test Description

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

  1. 2:  This step tests for a damaged terminal or connector in the TCM connector.
  2. 4:  This step tests for an open/short.
DTC P1688

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 a 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 data.
  3. Record the DTC Freeze Frame and Failure Records.
  4. Turn OFF the ignition.
  5. Disconnect the TCM connector C1 (GRAY).
  6. Inspect the C1 connector terminal 9 for a pulled back, unlocked, terminal or visible terminal damage.
Did you find and correct a condition?		 - Go to Step 8  Go to Step 3 
3
  1. Disconnect the PCM connector C2 (RED).
  2. Inspect terminal 2 for a pulled back, unlocked, terminal or visible terminal damage.
Did you find and correct a condition?		 - Go to Step 8  Go to Step 4 
4 
  1. Turn OFF the ignition.
  2. Disconnect the TCM connector C1 (GRAY) and the PCM connector C2 (RED).
  3. Using a DMM, test the unmanaged torque signal circuit between terminal 9 of the TCM and terminal 2 of the PCM for a short to ground or open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct a condition?		 - Go to Step 8  Go to Step 5 
5 Verify that the PCM has the proper model year software and calibration. This wiring option is only used with the 8.1L gas engine.
Was the software and calibration current and proper for the engine?		 - Go to Step 7  Go to Step 6 
6 Install the correct PCM calibration. Refer to Powertrain Control Module (PCM) Programming.
Is the calibration complete?		 - Go to Step 8  -
7 Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement in Engine Controls - 8.1L.
Did you complete the replacement?		 - Go to Step 8  -
8 Perform the following procedure in order to verify the repair:
  1. Select DTC.
  2. Select Clear Info.
  3. Operate the vehicle under the following conditions:
    • Vehicle at operating temperature
    • Engine speed greater than 200 RPM
    • All conditions are met for 2 seconds
  4. Select Specific DTC.
  5. Enter DTC P1688.

Has the test run and passed?		 - System OK Go to Step 1 
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