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Diagnostic Procedures

WARNING: This page is about a different car, the 2003 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
  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. Inspect for the following conditions:
    • Vacuum hoses that are disconnected, damaged, or incorrectly routed.
    • Manifold Absolute Pressure (MAP) sensor seal missing or damaged.
    • Restrictions in the MAP sensor vacuum source.
    • Intake manifold vacuum leaks.

    Did you find and correct the condition? If yes, go to step  25. If no, go to next step.

    3. NOTE: The vehicle used for the comparison is not limited to the same type of vehicle as is being serviced. A vehicle known to provide an accurate reading is acceptable.
  3. Do you have access to another vehicle in which the MAP sensor pressure can be observed with a scan tool? If yes, go to next step. If no, go to step  5.
  4. Turn ignition ON, with the engine OFF. Observe MAP sensor pressure with a scan tool. Observe MAP sensor pressure in the known good vehicle with a scan tool. Compare the values. Is the difference between the values less than 3 kPa? If yes, go to step  6. If no, go to step  11.
    5. NOTE: The Altitude vs. Barometric Pressure table indicates a pressure range for a given altitude under normal weather conditions. Weather conditions consisting of very low or very high pressure and/or very low or very high temperature may cause a reading to be slightly out of range.
  5. Turn ignition ON, with the engine OFF. Observe MAP sensor pressure with a scan tool. MAP sensor pressure should be within the range specified for your altitude. See Figure. Does the MAP sensor indicate the correct barometric pressure? If yes, go to next step. If no, go to step  11.
  6. Observe MAP sensor pressure with a scan tool. Start the engine. Does MAP sensor pressure change? If yes, go to next step. If no, go to step  11.
  7. Turn ignition OFF and remove the MAP sensor from the intake manifold. See appropriate article in ENGINES. Leave MAP sensor connected to the electrical harness and connect the Vacuum Pump to the MAP sensor port. Turn ignition ON, with the engine OFF. Observe the MAP sensor pressure with the scan tool. Apply vacuum to the MAP sensor in 1 in. Hg increments until 15 in. Hg is reached. Each 1 in. Hg should decrease MAP sensor pressure by 3-4 kPa. Is the decrease in MAP sensor pressure consistent? If yes, go to next step. If no, go to  11.
  8. Observe MAP sensor pressure with the scan tool. Apply vacuum with the Vacuum Pump until 20 in. Hg is reached. Is MAP sensor pressure less than 34 kPa? If yes, go to next step. If no, go to step  11.
  9. Observe MAP sensor pressure with the scan tool. Disconnect Vacuum Pump from MAP sensor. Does MAP sensor pressure return to the original reading observed in step  4 or  5 ? If yes, go to next step. If no, go to step  23.
  10. Inspect for the following conditions:
    • Incorrect cam timing.
    • Restricted exhaust flow.
    • Worn piston rings.

    Did you find and correct the condition? If yes, go to step  25. If no, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM.

  11. Disconnect MAP sensor electrical connector. Observe MAP sensor voltage with the scan tool. Is voltage less than 0.1 V? If yes, go to next step. If no, go to step  16.
  12. Measure the voltage between the MAP sensor 5-volt reference circuit and a good ground. Is voltage greater than 5.2 V? If yes, go to step  17. If no, go to next step.
  13. Probe the MAP sensor 5-volt reference circuit with a test light that is connected to a good ground. Is the test light OFF? If yes, go to step  18. If no, go to next step.
  14. Connect a 3-amp fused jumper wire between the MAP sensor 5-volt reference circuit and the MAP sensor signal circuit. Observe MAP sensor voltage with the scan tool. Is voltage greater than 4.9 V? If yes, go to next step. If no, go to step  19.
  15. Turn ignition OFF and remove the jumper wire. Remove MAP sensor form the intake manifold, unless the sensor was already removed in a previous step. Connect a jumper wire between each of the terminals in the MAP sensor harness connector and the corresponding terminal at the MAP sensor. Measure the voltage between the MAP sensor low reference circuit, at the jumper wire terminal, and a good ground. Is voltage greater than 0.2 V? If yes, go to step  20. If no, go to step  21.
  16. Test MAP sensor signal circuit between the PCM and MAP sensor for a short to voltage. Did you find and correct the condition? If yes, go to step  25. If not, go to step  24.
  17. Test all the branches of the 5-volt reference circuit that, are shared with the MAP sensor, for a short to voltage. Did you find and correct the condition? If yes, go to step  25. If no, go to step  24.
  18. Test the 5-volt reference circuit between the PCM and MAP sensor for an open or for high resistance. Did you find and correct the condition? If yes, go to step  25. If no, go to step  22.
  19. Test MAP sensor signal circuit between the PCM and MAP sensor for a short to ground, an open or high resistance. Did you find and correct the condition? If yes, go to step  25. If no, go to step  22.
  20. Test the low reference circuit between the PCM and MAP sensor for an open or high resistance. Did you find and correct the condition? If yes, go to step  25. If not, go to step  22.
  21. Test for an intermittent and/or poor connections at the MAP sensor. Did you find and correct the condition? If yes, go to step  25. If not, go to step  23.
  22. Test for an intermittent and/or poor connections at the PCM. Did you find and correct the condition? If yes, go to step  25. If not, go to step  24.
  23. Replace MAP sensor. See MANIFOLD ABSOLUTE PRESSURE SENSOR under SENSORS in REMOVAL & INSTALLATION - CORVETTE article. Did you complete the replacement? If yes, go to step  25.
  24. 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.
  25. 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.
  26. 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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