A L L Diagnostic Trouble Codes ( DTC ): Testing and Inspection

VACUUM CHECK

Vacuum circuit is monitored by the MAP sensor. A vacuum leak will cause a steady "CHECK ENGINE" light that will not go "OFF" by changing the throttle. It takes 10 seconds to get the CEL after a leak is detected. The CEL will only go "OFF" after the key is turned "OFF". Vacuum is supplied by the mechanical vacuum pump driven by the engine.

Fig. 031 - Chart For Vacuum Check.:

1. Checks to see if there is good source vacuum. 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 goes above 10" after 10 seconds (when CEL comes "ON"), leak is most likely on valve side of solenoids.
2. Checks for leak in EGR vacuum circuit, which includes MAP sensor and vacuum connections. Vacuum should hold if a good circuit is present.
3. Checks for leak in EPR vacuum circuit. Vacuum should hold if a good circuit is present.
4. Checks to see if vacuum leak is in vacuum source circuit or EGR/EPR solenoid. By removing solenoid connections and plugging source side vacuum, the reading for a good source vacuum should be over 10" vacuum, indicating leak is in the solenoid. VIN T, VIN V