Diagnostic Procedures
WARNING: This page is about a different car, the 2002 GMC Sierra, 2002 GMC Cab & Chassis Sierra, 2002 Chevrolet Silverado, and 2002 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
- Did you perform the Diagnostic System Check-Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM.
- Install a scan tool. Start the engine. Monitor the Diagnostic Trouble Code (DTC) Information using the scan tool. Does the scan tool indicate that DTC P1639 is current? If yes, see DTC P1639: 5-VOLT REFERENCE 2 CIRCUIT . If no, go to next step.
- Observe the BARO sensor pressure with a scan tool. Does the scan tool indicate that the pressure is less than 44 kPa? If yes, go to step 5. If no, go to next step.
- Observe the Freeze Frame/Failure Records for this DTC. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC or as close to the Freeze Frame/Failure Records data that you observed. Does the DTC fail this ignition cycle? If yes, go to next step. If no, see INTERMITTENT CONDITIONS under SELF-DIAGNOSTIC SYSTEM.
- Turn OFF the ignition. Disconnect the MAP sensor electrical connector. Turn ON the ignition, with the engine OFF. Measure the voltage from the 5-volt reference circuit of the MAP sensor to a good ground. Does the voltage measure near 5 V? If yes, go to next step. If no, go to step 7.
- Connect a 3-amp fused jumper wire between the 5-volt reference circuit of the BARO sensor and the signal circuit of the BARO sensor. Does the scan tool indicate that the BARO sensor pressure is more than 110 kPa? If yes, go to step 9. If no, go to step 8.
- Test the 5-volt reference circuit of the BARO sensor for a high resistance or an open. Did you find and correct the condition? If yes, go to step 13. If no, go to step 10.
- Test the signal circuit of the BARO sensor for a short to ground, low reference or an open. Did you find and correct the condition? If yes, go to step 13. If no, go to step 10.
- Inspect for poor connections at the BARO sensor. Did you find and correct the condition? If yes, go to step 13. If no, go to step 11.
- Inspect for poor connections at the ECM. Did you find and correct the condition? If yes, go to step 13. If no, go to step 12.
- Replace the BARO sensor. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to step 13.
- Replace the ECM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram ECM. See ENGINE CONTROL MODULE under PROGRAMMING. After repairs, go to next step.
- Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step 2.
- Observe the stored information, Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.