Vacuum Check
The Vacuum Circuit is monitored by the MAP sensor. A vacuum leak will cause a steady CEL that will not turn "OFF" by changing the throttle.
- This step checks for a vacuum source. Waiting 10 seconds allows the ECM to recognize a vacuum leak and shut EPR/EGR "OFF" if a leak is present. If vacuum is low, then becomes more than 10 in. Hg after 10 seconds (when CEL comes "ON") leak is most likely on valve side of solenoids.
- This step checks for leak in EGR vacuum circuit, which includes MAP sensor and vacuum connections. Vacuum should hold if a good circuit is present.
- This step checks for leak in EPR vacuum circuit. Vacuum should hold if circuit is good.
- This step checks if vacuum leak is in vacuum source circuit or EGR/EPR solenoid. By removing solenoid connections and plugging source side vacuum, normal reading for a source vacuum should be more than 10 in. Hg. This indicates that the leak is in the solenoid.