Mike's Workshop Manuals: Service manuals for every vehicle
Home >> Buick >> 2007 >> Allure CX >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System & Fuel System - 3.8L - Troubleshooting & Diagnosis >> Manifold Absolute Pressure Sensor Diagnosis >> Circuit/System Testing

Circuit/System Testing

Always perform the Diagnostic System Check - Vehicle .

  1. Start the engine.
  2. Monitor the DTC information with the scan tool.
  3. If DTC P0641 or P0651 is also set then correct DTC P0641 or P0651 first.
  4. Inspect for the following conditions:
    • Disconnected, damaged, or incorrectly routed vacuum hoses
    • MAP sensor disconnected from the vacuum source
    • Restrictions in the MAP sensor vacuum source
    • Intake manifold vacuum leaks
    • Inspect for a properly functioning oxygen sensor.
  5. With the ignition ON, and the engine OFF.
  6. Disconnect the MAP sensor.
  7. Measure for 4.8-5.2 volts from the 5-volt reference circuit of the MAP sensor to a good ground, with a DMM.
    • If more than 5.2 volts, then test the circuit for a short to voltage. If the circuit tests normal, replace the control module.
    • If less than 4.8 volts, then test the circuit for high resistance, an open, a short to ground, or an intermittent and poor connection or at the control module. If the circuit tests normal, replace the control module.
  8. Use a scan tool and observe the MAP sensor for less than 12 kPa.
    • If the MAP sensor is more than 12 kPa then test the MAP sensor signal circuit for a short to voltage. If the circuit tests normal, replace the control module.
  9. Use a 3-amp fused jumper wire and connect it between the MAP sensor 5-volt reference circuit and the MAP sensor signal circuit.
  10. Use a scan tool and observe the MAP sensor for more than 103 kPa.
    • If the MAP sensor is less than 103 kPa, then test the MAP sensor signal circuit for a short to ground, an open, high resistance. If the circuit tests normal, replace the control module.
  11. Turn OFF the ignition and allow the control module to power down.
  12. Remove the MAP sensor from the engine vacuum source. Leave the MAP sensor connected to the engine harness.
  13. Connect a J 23738-A  to the MAP sensor. See Special Tools .
  14. Turn ON the ignition, with the engine OFF.
  15. Observe the MAP sensor pressure with the scan tool.
  16. Apply vacuum to the MAP sensor with the J 23738-A  in 1 inch Hg increments until 15 inches Hg is reached. See Special Tools . Each 1 inch Hg should decrease MAP sensor pressure by 3-4 kPa. Monitor the MAP sensor pressure to see if the decrease in pressure is consistent.
    • If decrease in pressure is not consistent then, test for intermittent and poor connections at the MAP sensor. If connections test OK, replace the MAP sensor
  17. Apply vacuum with the J 23738-A  until 20 inches Hg is reached. See Special Tools . Observe the MAP sensor pressure for less than 34 kPa.
    • If more than 34 kPa, test for an intermittent and for a poor connection at the MAP sensor. If connections test OK, replace the MAP sensor.
  18. With a DMM measure for less than 5 ohms of resistance between the low reference circuit of the MAP sensor and battery negative post.
    • If the resistance is more than 5 ohms, then test the low reference circuit for a high resistance. If the circuit tests normal, replace the control module.
scientia non olet · About Mike's Workshop Manuals