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Diagnostic Procedure

WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, and 2003 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 the scan tool. Turn ignition on, engine off. Record the DTC failure records. If other DTCs are present, refer to the applicable DTC before continuing. Using a DVOM, measure and record the voltage between the battery terminals. Is the voltage greater than 10.5 volts? If so, go to step  4. If not, test battery. See appropriate GENERATORS & REGULATORS article in STARTING & CHARGING SYSTEMS. If okay, go to next step.
  3. Start the engine and warm to normal operating temperature. Is the Alternator or Check Engine lamp on? If so, see appropriate GENERATORS & REGULATORS article in STARTING & CHARGING SYSTEMS. If not, go to next step.
  4. Increase the engine speed to 1000-1500 RPM. Observe the system voltage on the scan tool. Is the voltage 13-15 volts? If so, go to next step. If not, see appropriate GENERATORS & REGULATORS article in STARTING & CHARGING SYSTEMS.
  5. Turn ignition off. Disconnect the C1 connector from the TCM additional DTCs may set, and install Breakout Box (J-39700) and Breakout Box Adapter (J-43799). Using a DVOM, measure the voltage between connector TCM connector C1 terminals No. 1 and 2 (with ignition on) and TCM connector C1 terminals No. 1 and 3 (with the ignition off). Compare the battery voltage to the wire voltage. Is the voltage difference greater than 0.5 volt? If so, go to next step. If not, go to step  7.
  6. Inspect and repair the transmission wiring harness assembly. Replace the wiring harness if necessary. Is the repair complete? If so, go to step  8.
  7. Replace the TCM. See TRANSMISSION CONTROL MODULE  under REMOVAL & INSTALLATION. Is the replacement complete? If so, go to next step.
    CAUTION: In most cases, the TCM is not at fault. Investigate thoroughly before replacing the TCM.
  8. Perform the following procedure to verify the repair:
    • Clear the DTC.
    • Start the engine and warm to normal operating temperature.
    • The system voltage, as indicated by the scan tool, should be 9-18 volts.

    Check for the DTC. Has the test passed? If so, system is okay. If not, go to step  1.

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