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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 73 (Automatic Transmission Diagnosis - 4L80-E (Gasoline)) >> Diagnostic Tests >> DTC P1860: TCC PWM Solenoid Circuit - Electrical Malfunction >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2002 GMC Cab & Chassis Sierra and 2002 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the diagnostic system check? If so, go to next step. If not, see DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
  2. Install a scan tool. Turn ignition on, engine off. Before clearing the DTCs, use the scan tool to record the freeze frame and failure records. Using the CLEAR INFO function erases the freeze frame and failure records from the PCM. Record the freeze frame and failure records. Clear the DTCs. Inspect the transmission fuse. Is the fuse open? If so, go to next step. If not, go to step  4 .
  3. Inspect the following components for a short to ground:
    • The Off/Run/Crank Voltage Circuit (1020)
    • The 1-2 Shift Solenoid
    • The 2-3 Shift Solenoid
    • The TCC PWM Solenoid
    • The Transmission Internal Wiring Harness Assembly

    Did you find and correct the condition? If so, go to step  20 . If not, see DIAGNOSTIC AIDS  .

  4. Turn ignition off. Disconnect the transmission in-line 20-way connector. Additional DTCs may set. Install the Jumper Harness (J-44152) on the engine side of transmission in-line 20-way connector. Turn ignition on, engine off. Connect a test light from the jumper harness terminal "E" to ground. Does the test light illuminate? If so, go to step  6 . If not, go to next step.
  5. Repair the open or high resistance in the TCC PWM solenoid valve voltage circuit (1020). Did you complete the repair? If so, go to step  20 .
  6. Install the test light from jumper harness terminal "E" to "S". Using the scan tool, command the TCC PWM solenoid valve on and off 3 times. Does the test light illuminate when you command the TCC PWM solenoid valve on, and go out when you command the TCC PWM solenoid valve off? If so, go to step  10 . If not, go to next step.
  7. Is the test light always on? If so, go to step  9 . If not, go to next step.
  8. Test the TCC PWM solenoid valve control circuit (418) for an open or short to power between the PCM connector C2 and the transmission in-line 20-way connector. Did you find and correct the condition? If so, go to step  20 . If not, go to next step.
  9. Test the TCC PWM solenoid valve control circuit (418) for an open or short to ground. Repair the circuit if necessary. Did you find and correct the condition? If so, go to step  20 . If not, go to step  11 .
  10. Install the jumper harness on the transmission side of the transmission in-line 20-way connector. Using a DVOM and Connector Test Adapter Kit (J-35616-A), measure the resistance between terminals "E" and "S". Does the resistance measure 10-15 ohms? If so, go to step  13 . If not, go to step  12 .
  11. Replace the PCM. See POWERTRAIN CONTROL MODULE  under REMOVAL & INSTALLATION. Did you complete the replacement? If so, go to step  20 .
  12. Disconnect the wiring harness at the TCC PWM solenoid valve. Measure the resistance of the TCC PWM solenoid valve. Does the resistance measure 10-15 ohms? If so, go to step  14 . If not, go to step  18 .
  13. Measure the resistance between jumper harness terminal "S" and ground. Does the resistance measure greater than 250 k/ohms? If so, go to step  16 . If not, go to step  15 .
  14. Test the transmission internal wiring harness assembly for an open circuit. Did you find a condition? If so, go to step  19 .
  15. Disconnect the wiring harness at the TCC PWM solenoid valve. Measure the resistance between each of the component terminals and ground. Do both readings measure greater than 250 k/ohms? If so, go to step  17 . If not, go to step  18 .
  16. Measure the resistance between jumper harness terminal "S" and all other terminals, except terminals "A", "B", and "E". Is the resistance between terminal "S" and any other terminal, except terminals "A", "B", and "E", less than 250 k/ohms? If so, go to next step. If not, see DIAGNOSTIC AIDS  .
  17. Test the transmission internal wiring harness assembly for a short to ground. Did you find a condition? If so, go to step  19 .
  18. Replace the TCC PWM solenoid valve. See SOLENOID VALVES  under REMOVAL & INSTALLATION. Did you complete the replacement? If so, go to step  20 .
  19. Replace the transmission internal wiring harness assembly. See TRANSMISSION INTERNAL WIRING HARNESS  under REMOVAL & INSTALLATION. Did you complete the replacement? If so, go to next step.
  20. Perform the following procedure to verify the repair:
    • Select DTC.
    • Select CLEAR INFO.
    • Select the parameters: TCC DUTY CYCLE, TCC DUTY CYCLE OPEN/SHORT TO GND and TCC DUTY CYCLE SHORTED TO VOLTS.
    • Operate the vehicle.
    • The TCC PWM solenoid valve is commanded on and TCC DUTY CYCLE SHORT TO VOLTS is "NO".
    • The TCC PWM solenoid valve is commanded off and TCC DUTY CYCLE OPEN/SHORT TO GND is "NO".
    • Each condition is met for 5 seconds.
    • Select SPECIFIC DTC.
    • Enter DTC P1860.

    Has the test run and passed? If so, system is okay. If not, go to step  1 .

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