Chart C5, Vacuum Control Check
During normal operation, the ECM compares its EGR duty cycle signal with MAP absolute pressure signal and makes corrections in duty cycle accordingly. If actual EGR control pressure (line vacuum) varies more than 2.4 in. Hg from what ECM has previously determined pressure should be, and variance continues for more than 10 seconds, a Code 53 will be set and ECM will shut down the EGR. The CEL will remain on and EGR off until the ignition switch is cycled off.
NOTE:
The following step numbers refer to the numbers in the accompanying flow chart(s).
- Checks if there is good source of vacuum.
- Tests MAP sensor's ability to recognize a vacuum leak and ECM's ability to control EGR.
- Breaks vacuum circulating into 2 parts: supply and EGR/EPR circuit. If vacuum increases when hose is pinched closed, leak is not on supply side.
NOTE:
Vacuum readings must be observed immediately (within 10 seconds) because ECM will stop PWM signal to EGR solenoid if MAP sensor signal voltage increases sufficiently above calibrated value, indicating a vacuum leak. If leak is between EGR solenoid and EGR valve, test will not work.