EPR Vacuum Circuit Check

The Exhaust Pressure Regulation (EPR) solenoid controls vacuum to EPR valve. When energized, EPR solenoid allows vacuum to close EPR valve, increasing exhaust backpressure for proper EGR operation.

EPR valve is a combination vacuum actuator and exhaust restrictor plate. When vacuum is applied to actuator, restrictor plate closes to increase exhaust system backpressure to allow EGR valve to function more efficiently.

1. This tests for normal EPR vacuum at idle. Since electrical circuit was already proven okay in EPR SOLENOID ELECTRICAL CHECK chart, absence of vacuum is due to no vacuum source (vacuum pump), or a restriction or leak in vacuum hose to valve, including a leak in solenoid.
2. EPR solenoid is de-energized, no vacuum should be present.
3. This tests for normal operation of EPR valve. When vacuum is applied to vacuum valve, valve actuator should move and hold.

Fig 1: Schematic, EPR Vacuum Circuit ("C" & "K" Series)

Courtesy of GENERAL MOTORS CORP.

Fig 2: Schematic, EPR Vacuum Circuit ("G" Series)

Courtesy of GENERAL MOTORS CORP.

Fig 3: Flowchart, EPR Vacuum Circuit

Courtesy of GENERAL MOTORS CORP.