Exhaust Gas Recirculation (EGR) System Check

INCORRECT EGR OPERATION:

1. If too much EGR is flowing at idle, cruise, or cold operation,
any of the following conditions could exist:
a. The engine dies after cold start.
b. The engine stalls on deceleration.
c. The vehicle surges during cruise mode.
d. Rough idle.

2. If too little or no exhaust gases flow, the combustion chamber temperature may increase under acceleration or heavy load conditions. These conditions could cause:
a. Detonation (Spark Knock).
b. The engine to overheat.
c. The emissions test to fail.

Chart C-7:

EGR Solenoid Wiring Diagram:

EGR SYSTEM CHECK

CIRCUIT DESCRIPTION:

The ECM operates a vacuum solenoid to control the EGR valve. The solenoid is normally closed. The ECM provides a ground path to energize the solenoid. This allows vacuum to flow to the EGR valve. The ECM controls the operation of the EGR valve based on input from the following sensors:

1. The Coolant Temperature Sensor (CTS) sensed a temperature value above 25~C (77~F).
2. The Throttle Position Sensor (TPS) sensed an off idle condition.
3. The Manifold Absolute Pressure (MAP) sensor is sending the proper signal to the ECM.




TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

1. Grounding the diagnostic test terminal should allow the EGR solenoid to energize, and vacuum should flow to the EGR valve.
2. When the diagnostic test terminal is not grounded, the vacuum should bleed off through a vent in the EGR solenoid, and the EGR valve should close.
3. This test determines if the electrical control portion of the system is at fault, or if the EGR solenoid and/or connector is at fault.
4. This system uses a negative back pressure EGR valve which should hold vacuum when the engine is not running.
5. Once vacuum has been applied to the valve, start the engine and note EGR diaphragm movement. Vacuum should bleed off and the EGR valve should close.

NOTE: Once the test sequence is completed, clear codes and verify NO "SERVICE ENGINE SOON" light exist.




DIAGNOSTIC AIDS:

1. Vacuum hoses should be thoroughly inspected for internal restrictions in the EGR system.
2. The ECM uses the Manifold Absolute Pressure (MAP) sensor for checking EGR operation.
3. If no problems are found, see DIAGNOSIS BY SYMPTOM.