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Home >> Chevrolet >> 2003 >> Corvette Base, 2D Convertible, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics >> Diagnostic Tests >> DTC P1639: 5-Volt Reference B Circuit >> Diagnostic Procedures

Diagnostic Procedures

  1. 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.
  2. Observe the Freeze Frame and/or Failure Records data for this DTC. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC fail this ignition cycle? If yes, go to next step. If no, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM.
  3. Turn ignition OFF. Disconnect the A/C pressure sensor electrical connector. Turn ignition ON, with engine OFF. Measure the voltage between the 5-volt reference circuit and engine ground. Is voltage 4.8-5.2 V? If yes, go to next step. If no, go to step  5.
  4. Connect the A/C pressure sensor. Disconnect the FTP sensor. Measure the voltage from the FTP sensor 5-volt reference circuit and a good ground. Is the voltage 4.8-5.2 V? If yes, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM. If no, go to step  11.
  5. Is the voltage measured in step 3 more than 5.2 V? If yes, go to step  8. If no, go to next step.
  6. Monitor the voltage while disconnecting the FTP sensor. Does the voltage return to 4.8-5.2 V when the FTP is disconnected? If yes, go to step  10. If no, go to next step.
  7. Turn ignition OFF. Disconnect the PCM. Test the 5-volt reference circuit for a short to ground or any sensor low reference circuit. Did you find and correct the condition? If yes, go to step  13. If no, go to step  12.
  8. Turn ignition OFF. Disconnect PCM. Turn ignition ON, with engine OFF. Test all 5-volt reference circuits for a short to voltage. Did you find and correct the condition? If yes, go to step  13. If no, go to next step.
  9. Test the FTP sensor signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step  13. If no, go to step  12.
  10. Replace the FTP sensor. See FUEL TANK PRESSURE SENSOR under SENSORS in REMOVAL & INSTALLATION - CORVETTE article. Did you complete the replacement? If yes, go to step  13.
  11. Replace the A/C pressure sensor. See appropriate article in HVAC. Did you complete the replacement? If yes, go to step  13.
  12. Replace PCM. See POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL & INSTALLATION - CORVETTE article. Did you complete the replacement? If yes, go to next step.
  13. 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 the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition cycle? If yes, go to step  2. If no, go to next step.
  14. Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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