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HOMESERVICE MANUALSCHEVROLET2001CHEVY EXPRESS G2500, VAN CARGO EXTENDED, 5.7 R, L31/KL8REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 72 (ENGINE CONTROL SYSTEM TESTING & ENGINE COMPONENT TESTING)ENGINE SENSORS & SWITCHESMANIFOLD ABSOLUTE PRESSURE SENSOR (3.5L & 3.8L)DIAGNOSTIC PROCEDURES
2001 Chevrolet Chevy Express G2500, Van Cargo Extended, 5.7 R, L31/KL8

Diagnostic Procedures

2001 Chevrolet Chevy Express G2500, Van Cargo Extended, 5.7 R, L31/KL8SECTION Diagnostic Procedures
WARNING: This page does not describe the selected car, but rather 31 other vehicles, including the 2002 Saturn SL2, 2002 Saturn SL1, 2002 Saturn SL, 2002 Saturn SC2, and 2002 Saturn SC1. 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 appropriate SELF-DIAGNOSTICS article. After performing Diagnostic System Check - Engine Controls, go to next step.
  2. Install a scan tool. Turn ON the ignition, with the engine OFF. With the scan tool, observe the MAP sensor pressure. Compare this value to a value observed in a known-good vehicle. Is the difference between the vehicles less than 3 kPa? If yes, go to next step. If no, go to step  7.
  3. Observe the MAP sensor pressure on the scan tool. Start the engine. Does the MAP sensor value change? If yes, go to next step. If no, go to step  7.
  4. Turn OFF the ignition. Remove the MAP sensor from the engine vacuum source. Leave the MAP sensor connected to the engine harness. Connect a Hand Vacuum Pump (J 23738-A) to the MAP sensor port. Turn ON the ignition, with the engine OFF. Observe the MAP sensor pressure as you slowly apply vacuum 1 in. Hg at a time. Each one inch of vacuum should result in a 3 to 4 kPa drop in the MAP sensor pressure. Does the scan tool indicate that the MAP sensor is operating normally? If yes, go to next step. If no, go to step  13.
  5. Observe the MAP sensor pressure on the scan tool with 20 in. Hg of vacuum applied to the sensor. Is the MAP sensor pressure less than 34 kPa? If yes, go to next step. If no, go to step  7.
  6. Disconnect the MAP sensor from the hand held vacuum pump. Does the MAP sensor pressure return to the value observed in step  2? If yes, system is okay. If no, go to step  13.
  7. Turn OFF the ignition. Disconnect the MAP sensor from the engine harness. Turn ON the ignition, with the engine OFF. Observe the MAP sensor voltage display on the scan tool. Is the voltage more than 0 V? If yes, go to step  10. If no, go to next step.
  8. Jumper the MAP sensor 5-volt reference circuit to the MAP sensor signal circuit using a fused jumper wire. Observe the MAP sensor voltage display on the scan tool. Is the voltage near 5 V? If yes, go to next step. If no, go to step  11.
  9. Remove the jumper. Probe the MAP sensor low reference circuit with a test lamp connected to battery positive voltage. Does the test lamp illuminate? If yes, go to step  13. If no, go to step  12.
  10. Test the signal circuit for a short to voltage. This short will have resistance as a complete short would have set a DTC. Did you find and correct the condition? If yes, go to step  17. If no, go to step  15.
  11. Test the 5-volt reference and the signal circuit for high resistance or an open. Did you find and correct the condition? If yes, go to step  17. If no, go to step  15.
  12. Test the MAP sensor low reference circuit for high resistance or an open. Did you find and correct the condition? If yes, go to step  17. If no, go to step  15.
  13. Inspect the MAP sensor connector for poor connection or terminal contact. Did you find and correct the condition? If yes, go to step  17. If no, go to next step.
  14. Replace the MAP sensor. After repairs, go to step  17.
  15. Inspect the PCM for poor connection or terminal contact. Did you find and correct the condition? If yes, go to step  17. If no, go to next step.
  16. Replace PCM. Program replacement PCM. See POWERTRAIN CONTROL MODULE under PROGRAMMING in appropriate SELF-DIAGNOSTICS article. After repairs, go to next step.
  17. Use the scan tool in order to clear the DTCs that may have set. Turn OFF the ignition for 30 seconds. Start the engine. Did you correct the condition? If yes, system is okay. If no, go to step  2.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.