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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. Check the transmission fluid level. See SERVICING - "C" & "K" SERIES (ALLISON) article. Is the transmission fluid level correct? If so, go to next step.
  3. Measure the line pressure. See HYDRAULIC PRESSURE TESTS  under PERFORMANCE TESTS. Is the pressure within the specified value? If so, go to next step. If not, see SYMPTOM DIAGNOSIS  under TROUBLE SHOOTING.
  4. This DTC is set when Reverse is selected, and the Reverse pressure switch status remains mechanically open or electrically off for more than 1.0 second. This DTC may also occur at shutdown where the switch remains in an open/off state. This DTC may indicate that an electrical open condition may exist in the Reverse pressure switch circuit or the pressure switch manifold. The intent of this DTC is to detect discrepancies between range selected at the PNP switch and the actual position of the manual selector valve. Go to next step.
  5. Turn ignition off. Disconnect the C2 connector from the TCM, and install Breakout Box (J-39700) and Breakout Box Adapter (J-43799). Disconnect the transmission in-line 20-way connector. Connect TCM connector C2 terminal No. 4 to a known-good ground. Turn ignition on. Does the scan tool indicate Reverse pressure switch status as ON? If so, go to next step. If not, go to step  12.
  6. Turn ignition off and reconnect the C2 connector to the TCM. Disconnect the transmission in-line 20-way harness connector. Connect a wire between engine side of transmission in-line 20-way harness connector terminal "K" to a known-good ground. Turn ignition on. Does the scan tool indicate Reverse pressure switch status as ON? If so, go to next step. If not, go to step  11.
  7. Remove the oil pan. See SERVICING - "C" & "K" SERIES (ALLISON) article. Disconnect the internal wiring harness from the pressure switch manifold, and ground pressure switch manifold connector terminal "D". Does the scan tool indicate Reverse pressure switch status as ON? If so, go to next step. If not, go to step  9.
  8. Replace the pressure switch manifold. See PRESSURE SWITCH MANIFOLD  under REMOVAL & INSTALLATION. Is the replacement complete? If so, go to step  13.
  9. Inspect the internal wiring harness for an open condition. Did you find a problem? If so, go to next step.
  10. Replace the internal wiring harness. See TRANSMISSION INTERNAL WIRING HARNESS  under REMOVAL & INSTALLATION. Is the replacement complete? If so, go to step  13.
  11. Repair the vehicle wiring harness. Is the repair complete? If so, go to step  13.
  12. 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.
  13. Perform the following procedure to verify the repair:
    • Clear the DTC.
    • Operate the vehicle under normal driving conditions.
    • Using the scan tool, monitor Reverse pressure switch operation.

    Did the DTC return? If so, go to step  1. If not, system is okay.

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