CIRCUIT DESCRIPTION:Code 63,64 and 65 are Exhaust Gas Recirculation (EGR) flow test failures. The ECM, on a close throttle coast down, will cycle the solenoids "ON and "OFF" individually and look for a resulting change in the engine rpm and 02 sensor activity.
TEST DESCRIPTION:Number(s) refer to circled number(s) on the diagnostic chart.
1. You should be able to discern a change in engine RPM as each solenoid id cycled "ON". Solenoid #1 should have the smallest change and #3 should have the smallest change and may even stall the engine.
2. Check for an open in RED,BLUE and BROWN wires on the EGR circuit, or a faulty ECM connection or ECM.
NOTE: If the digital EGR valve shows signs of excessive heat, a melted condition, check the exhaust system for blockage (possible a plugged converter) . If the exhaust system is restricted, repair the cause, one of which which might be an injector which is open due to one of the following:
B. grounded driver circuit
C. possible faulty ECM,
If this condition is found, the oil should be checked for possible fuel contamination.
An intermittent may be caused by a poor connection, rubbed-throught wire insulation, or a wire broken inside insulation.
* POOR CONNECTION OR DAMAGED HARNESS. Inspect ECM harness connection for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harmess.
* INTERMITTENT TEST. If connection and harness check OK, connect a digital voltmeter from effected terminals to ground while moving related connectors and wiring harness. if the failure is induced, the voltage reading will change.
PURPOSE The EGR system is used to lower NOx (oxides of nitrogen) emission levels caused by high combustion temperature. it does this by decreasing combustion temperature.
the main element of the system is the digital EGR valve.
the digital EGR valve feeds small amounts of exhaust gas back into the intake manifold and then into the combustion chamber.
OPERATION The digital EGR valve is designed to accurately supply EGR to an engine, independent of intake manifold vacuum. the valve controls EGR flow from the exhaust to the intake manifold through thress orifices, which increment in size, to produce seven combinations. when a solenoid is energized, the armature, with attached shaft and swival pintle, is lifted opening the orifice. The flow accuracy is dependent on metering orifice size only, which results in improved control.
The swivel pintle feature insures good sealing of exhaust gas, reducing the need of critical assembly alignment. in addition, the effects of EGR leakage on idle quality are reduce because the shaft and seals are exposed to exhaust pressure instead of manifold vacuum. the shafts are seal from the exhaust chamber by floating seals held in place by the seal spring. these springs also hold the upper seals that seal the armature cavity in the solenoids.
the solenoid coils are fastened together to maximize reliability and to seal the coil from the environment. the coil use a common power terminal with individual ground terminals.
the digital EGR valve is oprned by the ECM QDM, grounding each respective solenoid circuit. This activates the solenoid, raises the pintle, and allows exhaust gas flow into the intake manifold. the exhaust gas then moves with air/fuel mixture into the combustion chamber. if toomuch exhaust gas enter, combustion will not occur. for this reason, very little exhaust gas is allowed to pass throgh the valve, especially at idle. the EGR valve is usually open under the following conditions:
* warm engine operation.
* above idle speed.
to regulate EGR flow, the ecm controls the EGR solenoids to vary the amount of EGR flow. the EGR uses information from the following sensor to regulate the solenoid:
* coolant temperature sensor (CTS)
* throttle position sensor
* mass air flow (MAF) sensor
RESULTS OF INCORRECT EGR SYSTEM OPERATION
Too much EGR flow at idle, cruise, or cold operation, any of the following conditions may occur:
* engine stops after cold start
* engine stops at idle after deceleration
* rough idle.
too little or no EGR flow allows combustion temperatures to get too high. this could cause.
* spark knock (detonation)
* engine overheating.
* emission test failure.
A fuel pump with over a 100,000 mile will also cause a stalling situation dueing stopping while driving. Yes, the fuel pump will keep the car running and drivingO.K., and you will only notice the car will shut off "SOMETIME" when coming to a complete stop with no SES light. So a poor performaning fuel pump and clog gas filter will cause a stalling issue with no SES light.
SOURCE: GM SERVICE MANUAL.
Wiki Authors: SteveX,
Dates Modified: 4-20-08,
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