Component Diagnosis Charts - C3 System

Chart C-7, EGR Flow Check:

Digital EGR Valve Circuit Diagram:

CIRCUIT DESCRIPTION
EGR solenoid valves get battery power when the ignition is turned "ON" and become energized when the control module completes the circuit to ground. When a solenoid is energized, the armature, with attached shaft and swivel pintle, is lifted and the orifice is opened, allowing exhaust gas into the intake manifold. Three solenoid valves control exhaust gas flow to produce seven combinations of EGR flow. The control module should only open the valves when the engine is at operating temperature, above idle speed and a vehicle speed sensor signal is present.

TEST DESCRIPTION (using "SCAN" tool)
Numbers below refer to circled numbers on diagnostic chart.
1. You should be able to discern a change in engine speed as each solenoid is cycled "ON" and "OFF" again. The #3 solenoid may cause the engine to stall when cycled "ON" with the engine idling.
2. This step checks the wiring and the PCM's ability to complete the EGR solenoid circuits to ground. If the test light lights, the PCM and wiring are OK.

TEST DESCRIPTION (without "SCAN" tool)
1. FLOW CHECK - EGR solenoids can be cycled "ON" and "OFF" manually by using the following procedure.

A. Instead of using a "SCAN" tool, start engine and disconnect EGR solenoid harness connector.
B. With engine idling, connect fused battery power to terminal "D" of solenoid valve assembly (jumper terminal "D" of harness connector to terminal "D" of EGR valve connector).
C. Ground each of the other terminals of the solenoid valve assembly one at a time. Grounding terminal "A" energizes solenoid #1, terminal "B" energizes solenoid #2, terminal "C" energizes solenoid #3. You should be able to discern a change in engine speed as each solenoid is cycled "ON" and "OFF" again. The #3 solenoid may cause the engine to stall when cycled "ON" with the engine idling.

If there is no change in engine speed as one or more of the solenoids in energized, check for plugged orifice, plugged EGR passage, or faulty solenoid (perform electrical check.)

NOTE: Disconnecting the EGR connector with the engine running may cause a Code 56 to set.

2. ELECTRICAL CHECK
A. Turn ignition "ON", do not start engine.
B. Check for battery power at terminal "D" of EGR connector with a test light connected to ground. Test light should light. If not check for burned fuse or open circuit.
C. Back probe PCM terminals GC8, GC9, and GC10, with a test light connected to ground. Test lamp should light on all three terminals. If not, check for open in circuit that did not light test lamp. If no open circuit, possible faulty EGR solenoid, faulty PCM ground circuit, or faulty PCM.
D. Repeat step C and, while observing test light to each terminal, ground diagnostic test terminal of ALDL. Test lamp should go out as diagnostic terminal is grounded. If test lamp lights but does not go out when diagnostic terminal is grounded, faulty PCM ground connection or faulty PCM is indicated.

NOTE: If the digital EGR valve shows signs of excessive, check for restricted or plugged catalytic converter. If exhaust is restricted, repair the cause. Possible causes of restricted exhaust are:

Ignition Misfire
Excessive Rich Condition
Leaking Injector(s)
Grounded Injector Driver Circuit