Chart C-5 Vacuum Control Check: VIN N (5.7L) VIN T (4.3L)

Fig. 034 - WIRING DIAGRAM for Chart C-5 Vacuum Control Check. VIN N, VIN T:

CHART C-5

VACUUM CONTROL CHECK

4.3L VIN "T"

5.7L VIN "N"

During normal operation, the ECM compares its EGR duty cycle signal with the MAP absolute pressure signal and makes corrections in duty cycle accordingly. If the actual EGR control pressure (line vacuum) varies more than 8.11 KPA (2.4" HG) from what the ECM has previously determined the pressure should be and this variance continues for 10 seconds or more, a Code 53 will set and the ECM will shut down the EGR. The CEL will remain on and EGR off until the ignition switch is cycled off.

Fig. 033 - Chart C-5 Vacuum Control Check.:

1. Checks to see if there is good source vacuum.
2. Tests MAP sensor's ability to recognize a vacuum leak and ECM's ability to control EGR.
3. Breaks vacuum circuiting into two parts; supply and EGR/EPR circuit. If vacuum increases when hose is pinched closed, the leak is not on the supply side.

NOTE:
Vacuum readings must be observed immediately (within 10 seconds) because the ECM will stop the PWM signal to EGR solenoid if the MAP sensor signal voltage increases sufficiently above calibrated value, indicating a vacuum leak. Then if leak is between EGR solenoid and EGR valve, test will not work.