CHART A-1, NO MIL (SERVICE ENGINE SOON) LIGHT (WITH A/T)
MIL should be on when engine is off and ignition is on. Switched battery voltage is supplied to MIL. The ECM turns light on by providing a ground path through circuit No. 419.
Note. Test numbers refer to numbers on diagnostic chart.
- If fusible link is blown, see «WIRING DIAGRAMS»(ref-19441) article in this section for complete circuit.
- Using a test light connected to 12 volts, probe each of the system ground circuits to ensure a good ground is present. See «PIN VOLTAGE CHARTS»(ref-19442) article in this section.
CHART A-1, NO MIL (SERVICE ENGINE SOON) LIGHT (WITH M/T)
When engine is started, ECM grounds terminal A10 to turn off MIL. When DLC terminal "B" is grounded, ECM alternately grounds and opens terminal A10 to flash a DTC.
Note. Test numbers refer to numbers on diagnostic chart.
- This tests for an open ECM fuse or an open in MIL circuit, including instrument panel connector, printed circuit board, and bulb. Light on is normal response.
- This tests for a shorted ECM. A grounded ECM terminal A10 will cause MIL to go off. If light comes on after disconnecting ECM, ECM is shorted. Light on is normal response.
- This tests for a grounded circuit No. 487, between terminal "C" of MIL driver and ECM terminal A10. It also checks for an open circuit No. 439 to terminal "B" of MIL driver module, a bad ground, or a faulty MIL driver. Because of voltage drop through MIL driver upper resistor, a normal voltage reading should be 9-11 volts. If voltage is greater than 11 volts, there is no voltage drop in MIL driver module due to bad ground or faulty module.
- This tests for an open wire to MIL driver terminal "B". Normal reading should be close to battery voltage.
- This tests for a grounded circuit No. 487, between terminal "C" of MIL driver and ECM terminal A10. Light on is normal response.
Scheme 82
EPR SOLENOID ELECTRICAL 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. The solenoid is supplied with 12 volts by ignition switch. ECM completes ground circuit to energize solenoid, and turn EPR on when needed (EGR operation command).
Note. Test numbers refer to numbers on diagnostic chart.
- This tests for short to ground, or a faulty ECM signal to EPR solenoid. Test light should normally be off.
- This tests for signal to energize EPR solenoid with engine at idle. If test light is on, electrical circuits to solenoid are okay.
- This tests for voltage or open circuit from terminal "B" of EPR solenoid to ECM terminal C12 ("C" & "K" Series) or F16 ("G" Series) on circuit No. 439 ("C" & "K" Series) or No. 39 ("G" Series).
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.
Note. Test numbers refer to numbers on diagnostic chart.
- 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.
- EPR solenoid is de-energized, no vacuum should be present.
- This tests for normal operation of EPR valve. When vacuum is applied to vacuum valve, valve actuator should move and hold.
