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Diagnostic Procedure

WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2003 Pontiac Grand Prix, 2003 Pontiac Bonneville, 2003 Chevrolet Monte Carlo, 2003 Chevrolet Impala, and 2003 Buick Regal. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.8L BONNEVILLE, GRAND PRIX, IMPALA, LESABRE, MONTE CARLO, PARK AVENUE & REGAL article. After performing Diagnostic System Check - Engine Controls, go to next step.
  2. Check for the following conditions:
    • Vacuum hoses disconnected, damaged, or incorrectly routed.
    • 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  24. 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 using a scan tool? If yes, go to next step. If no, go to step  5.
  4. Turn ignition switch to RUN position, engine OFF. Observe the MAP sensor pressure using a scan tool. Observe the MAP sensor pressure in the known good vehicle using 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  10.
    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 switch to RUN position, engine OFF. Observe the MAP sensor pressure using a scan tool. See ALTITUDE VS. BAROMETRIC PRESSURE  table. The MAP sensor pressure should be within the range specified for your altitude. Does the MAP sensor indicate the correct barometric pressure? If yes, go to next step. If no, go to step  10.
  6. Observe the MAP sensor pressure using a scan tool. Start the engine. Does the MAP sensor pressure change? If yes, go to next step. If no, go to step  10.
  7. Turn ignition switch to OFF position. Remove the MAP sensor from the engine vacuum source. Leave the MAP sensor connected to the engine harness. Connect a hand vacuum pump to the MAP sensor. Turn ignition switch to RUN position, engine OFF. Observe the MAP sensor pressure using the scan tool. Apply vacuum to the MAP sensor using the hand vacuum pump in one in. Hg increments until 15 in Hg is reached. Each one 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 step  10.
  8. Apply vacuum using the hand vacuum pump until 20 in Hg is reached. Is the MAP sensor pressure less than 34 kPa? If yes, go to next step. If no, go to step  10.
  9. Disconnect the hand vacuum pump from the MAP sensor. Does the MAP sensor pressure return to the value observed in step  4 or  5 ? If yes, system is okay at this time. If no, go to step  12.
  10. Disconnect the MAP sensor harness connector. Observe the MAP sensor parameter using the scan tool. Is the voltage less than 0.1 volt? If yes, go to next step. If no, go to step  15.
  11. Measure the voltage from the 5-volt reference circuit of the MAP sensor to a good ground using a DVOM. Is the voltage more than 5.2 volts? If yes, go to step  16. If no, go to next step.
  12. Probe the 5-volt reference circuit of the MAP sensor using a test light connected to a good ground. Is the test light OFF? If yes, go to step  17. If no, go to next step.
  13. Connect a 3-amp fused jumper wire between the MAP sensor 5-volt reference circuit and the MAP sensor signal circuit. Observe the MAP sensor parameter using the scan tool. Is the voltage more than 4.9 volts? If yes, go to next step. If no, go to step  18.
  14. Turn ignition switch to OFF position. Remove the jumper wire. Connect a jumper wire between each of the terminals in the MAP sensor harness connector and the corresponding terminal at the MAP sensor. Turn ignition switch to RUN position, engine OFF. Measure the voltage from the MAP sensor low reference circuit at the jumper wire terminal to a good ground using a DVOM. Is the voltage more than 0.2 volt? If yes, go to step  19. If no, go to step  20.
    15. NOTE: Disconnecting the PCM may eliminate the short during testing. The MAP sensor may have been damaged if the circuit was shorted to a voltage source.
  15. Check the MAP sensor signal circuit between the PCM and the MAP sensor for a short to voltage. Did you find and correct the condition? If yes, go to step  17. If no, go to next step.
    16. NOTE: Disconnecting the PCM may eliminate the short during testing. The MAP sensor may have been damaged if the circuit was shorted to a voltage source.
  16. Check all of 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  24. If no, go to step  23.
  17. Check the 5-volt reference circuit between the PCM and the MAP sensor for an open or for high resistance. Did you find and correct the condition? If yes, go to step  24. If no, go to step  21.
  18. Check the MAP sensor signal circuit between the PCM and the MAP sensor for a short to ground, an open or high resistance. Did you find and correct the condition? If yes, go to step  24. If no, go to step  21.
  19. Check the low reference circuit between the PCM and the MAP sensor for high resistance or an open. Did you find and correct the condition? If yes, go to step  24. If no, go to step  21.
  20. Check for an intermittent and for a poor connection at the MAP sensor. Did you find and correct the condition? If yes, go to step  24. If no, go to step  22
  21. Check for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step  24. If no, go to step  23.
  22. Replace the MAP sensor. After repair, go to step  24.
  23. Replace PCM. Program replacement PCM. See POWERTRAIN CONTROL MODULE under PROGRAMMING in SELF-DIAGNOSTICS - 3.8L BONNEVILLE, GRAND PRIX, IMPALA, LESABRE, MONTE CARLO, PARK AVENUE & REGAL article. After repair, go to next step.
  24. Use the scan tool to clear the DTCs that may have set. Turn ignition switch to OFF position for 30 seconds. Start the engine. Did you correct the condition? If yes, system is okay at this time. If no, go to step  2.
ALTITUDE VS. BAROMETRIC PRESSURE (1)

Altitude - Meters Altitude - Feet Barometric Pressure - kPa
4267 14000 56-64
3962 13000 58-66
3658 12000 61-69
3353 11000 64-72
3048 10000 66-74
2743 9000 69-77
2438 8000 71-79
2134 7000 74-82
1829 6000 77-85
1524 5000 80-88
1219 4000 83-91
914 3000 87-95
610 2000 90-98
305 1000 94-102
0 0 (Sea Level) 96-104
-305 -1000 101-105
(1) Determine your altitude by contacting a local weather station or by using another reference source.
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