EPR Electrical Check
The EPR solenoid controls vacuum to EPR valve. EPR solenoid, when energized, allows engine vacuum pump vacuum to close EPR valve. Battery voltage is supplied from ignition, and ECM completes the ground to energize solenoid. ECM will not recognize an electrical fault in EPR circuit, but will detect a vacuum leak causing no EPR. The EPR is turned "OFF" by ECM when engine temperature is less than 125°F (52°C). Engine temperature switch, when closed, signals ECM that engine is cold.
- This step checks for a short to ground on ECM side of EPR solenoid, in wire to ECM, or ECM itself.
- This step checks for normal solenoid "ON" signal with engine running. Test light will normally be "ON" if both ignition circuit to terminal "A" of solenoid is complete, and ECM completes circuit to ground at solenoid terminal "B."
- This step checks for proper ECM control of EPR solenoid. Normal response above 2500 RPM is to shut EPR "OFF." The test light should normally be "OFF" above 2500 RPM.