Circuit/System Testing

Always perform the Diagnostic System Check - Vehicle .

1. Start the engine.
2. Monitor the diagnostic trouble code (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 vacuum source
   • Restrictions in the MAP sensor vacuum source
   • Intake manifold vacuum leaks
   • For properly functioning oxygen sensor, refer to SCAN TOOL DATA LIST
5. With the ignition ON, and the engine OFF.
6. Disconnect the manifold absolute pressure (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 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the control module.
   • If less than 4.8 volts, then test the 5-volt reference circuit for high resistance, an open, 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 or 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. With a DMM measure for less than 5 ohms of resistance between the low reference circuit of the MAP sensor and a good ground.
    • If the resistance is more than 5 ohms, then test the circuit for an open or high resistance. If the circuit tests normal, replace the control module.
13. Turn OFF the ignition.
14. Remove the MAP sensor from the engine vacuum source. Leave the MAP sensor connected to the engine harness.
15. Connect the J 23738-A  to the MAP sensor.
16. Turn ON the ignition, with the engine OFF.
17. Observe the MAP sensor pressure with a scan tool
18. Apply vacuum with the J 23738-A  to the MAP sensor in 1 inch Hg increments until 15 inch Hg is reached. 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 connection at the MAP sensor. If connections test OK, replace the MAP sensor.
19. Apply vacuum with J 23738-A until 20 inch Hg is reached. Observe the MAP sensor pressure for less then 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.