Chart C-4 EPR Solenoid Check: VIN N (5.7L) VIN T (4.3L)

Fig. 040 - WIRING DIAGRAM for Chart C-4 EPR Solenoid Check. VIN N, VIN T:

CHART C-4

EPR SOLENOID CHECK

4.3L VIN "T"

5.7L VIN "N"

The EPR solenoid controls vacuum to the EPR valve. The EPR solenoid, when energized, allows engine pump vacuum to close the EPR valve. The same vacuum source is used for both EGR and EPR solenoids. 12 volts is supplied from the ignition, and the ECM completes the ground to energize the solenoid. The ECM will not recognize an electrical fault in the EPR circuit, but will detect a vacuum leak causing no EPR. The EPR is turned "OFF" by the ECM when coolant temperature is below 40°C (104°F). The coolant temperature sensor signals the ECM that the engine is cold and EPR remains off until coolant temperature rises above that point.

Fig. 039 - Chart C-4 EPR Solenoid Check.:

1. Checks for a short to ground on ECM side of EPR solenoid, in the wire to the ECM or the ECM itself.
2. Checks for normal solenoid "ON" signal with engine running. The test light will normally be "ON" if both the ignition circuit to Terminal "A" of solenoid is complete, and the ECM completes the circuit to ground at solenoid Terminal "B".
3. Checks for proper ECM control of EPR solenoid. Normal response to above 2500 RPM is to shut EPR "OFF". The test light should normally be "OFF" above 2500 RPM.
4. Determines if fault is in EPR control lead or ECM.