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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 72 (Automatic Transmission Diagnosis - 4L80-E (Diesel)) >> Diagnostic Tests >> DTC P0723: OSS Sensor Circuit - Intermittent >> 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 DTC, use the scan tool to record the freeze frame and failure records for reference. The CLEAR INFO function will erase the data. Record the DTC freeze frame and failure records. Clear the DTC. Raise the drive wheels and support the axle assembly. Start the engine and place the gearshift lever in the "D1" position. Gradually increase the wheel speed. Does the transmission output speed increase with the drive wheel speed? If so, see DIAGNOSTIC AIDS  . If not, go to next step.
  3. Turn ignition off. Disconnect the OSS. Connect DVOM set to AC scale between OSS terminals. Start the engine, and place the gearshift lever in the "D1" position. With the wheels turning, slowly accelerate to 2000 engine RPM. Does the voltage measure greater than 2 volts AC at 2000 RPM? If so, go to next step. If not, go to step  14 .
  4. Connect the OSS sensor. Disconnect the VSS buffer harness from the VSS buffer. Connect DVOM set to AC scale between VSS buffer harness connector terminals No. 7 and 12. Start the engine, and place the gearshift lever in the "D1" position. With the wheels turning, slowly accelerate engine speed to 2000 RPM. Does the voltage measure greater than 2 volts AC at 2000 RPM? If so, go to step  7 . If not, go to next step.
  5. Test the OSS high (821) and low (822) signal circuits for an intermittent open circuit between the VSS buffer and the VSS sensor. Did you find and correct the condition? If so, go to step  17 . If not, go to next step.
  6. Test the OSS high (821) and low (822) signal circuits for an intermittent short together between the VSS buffer and the OSS. Did you find and correct the condition? If so, go to step  17 . If not, see DIAGNOSTIC AIDS  .
  7. Test the VSS buffer ignition "1" voltage circuit (39) for an intermittent high resistance or an open. Did you find and correct the condition? If so, go to step  17 . If not, go to next step.
  8. Test the VSS buffer ground circuit (451) for an intermittent high resistance or an open. Did you find and correct the condition? If so, go to step  17 . If not, go to next step.
  9. Disconnect the VSS buffer connector. Turn ignition on, engine off. Test the VSS buffer vehicle speed signal circuit (437) for an intermittent voltage between VSS buffer connector terminal No. 13 and a good ground. Does the voltage measure 4.8-5.2 volts DC? If so, go to step  13 . If not, go to next step.
  10. Does the voltage in step  9 measure greater than 5.2 volts DC? If so, go to step  12 . If not, go to next step.
  11. Test the VSS buffer vehicle speed signal circuit (437) for an intermittent short to ground between the PCM connector C2 terminal A3 and the VSS buffer. Did you find and correct the condition? If so, go to step  17 . If not, go to step  16 .
  12. Test the VSS buffer vehicle speed signal circuit (437) for an intermittent short to power between the PCM connector C2 terminal A3 and the VSS buffer. Did you find and correct the condition? If so, go to step  17 . If not, go to step  16 .
  13. Connect the VSS buffer harness connector to the speed buffer module. With the DVOM set to DC scale and on a good ground, backprobe VSS buffer module terminal No. 13. Start the engine, and place the gearshift lever in the "D1" position. With the wheels turning slowly, accelerate the engine speed to 2000 RPM. Does the voltage measure 1.5-3.5 volts DC? If so, go to step  16 . If not, go to step  15 .
  14. Replace the OSS. See SPEED SENSORS  under REMOVAL & INSTALLATION. Did you complete the replacement? If so, go to step  17 .
  15. Replace the VSS buffer module. See VSS BUFFER MODULE  under REMOVAL & INSTALLATION. Did you complete the replacement? If so, go to step  17 .
  16. Replace the PCM. See POWERTRAIN CONTROL MODULE  under REMOVAL & INSTALLATION. Did you complete the replacement? If so, go to next step.
  17. Perform the following procedure to verify the repair:
    • Select DTC.
    • Select CLEAR INFO.
    • Drive the vehicle under steady acceleration above 10 percent accelerator pedal position.
    • The PCM must see an output speed greater than 500 RPM for one second.
    • Select SPECIFIC DTC.
    • Enter DTC P0723.

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

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