System Diagnosis

Chart C-7 - EGR System Check:

Chart C-7 EGR VSV Schematic:

CIRCUIT DESCRIPTION:

The EGR Vacuum Switching Valve (VSV) solenoid is controlled by the ECM. The VSV solenoid is supplied with battery voltage and the ECM will switch to ground to turn the solenoid "ON" for EGR operation.

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

1. This test checks that the EGR valve is mechanically functional.

2. This test checks that vacuum is available to operate the EGR valve.

3. This test checks that the EGR (VSV) solenoid circuitry is operating properly.

DIAGNOSTIC AIDS:

NOTE: Before inspecting EGR system and VSV in California specification vehicles and EGR system in Federal specification vehicles, be sure to confirm the following:

^ With A/T vehicle, lock-up signal is not fed into ECM.
^ MAT sensor is working properly. If any of the above conditions are present, the system will not operate.

Be sure to check hoses for proper vacuum supply, plugged, kinked or deteriorated hoses.

If EGR valve in Federal specification fails to operate properly, any of the following areas could be the cause:

^ Vacuum hoses
^ EGR valve
^ EGR modulator
^ VSV (Vacuum Switching Valve)
^ 5th gear switch for M/T vehicle (Federal Spec only)
^ Lock-up signal for A/T vehicle (Federal Spec only)

RESULTS OF INCORRECT EGR SYSTEM OPERATION

Too much EGR flow tends to weaken combustion, causing the engine to run roughly or stop. With too much EGR flow at idle, cruise, or cold operation, any of the following conditions may happen:

^ Engine stops after cold start
^ Engine stops at idle after deceleration
^ Car surges during cruise
^ Rough idle (if the EGR valve should stay open all of the time, the engine may not idle).

Too little or no EGR flow allows combustion temperatures to get too high during acceleration and load conditions. This could cause:

^ Spark knock (detonation)
^ Engine overheating
^ Emission test failure