System Diagnosis

ON-VEHICLE SERVICE

EGR VALVE

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.

INSPECT:

NOTE: Before inspection, check to make sure that gear shift lever is in neutral position (with A/T vehicle, selector lever in "P" range) and that parking brake lever is fully applied.

1. When engine is cool (coolant temperature is below 45°C, (113°F)) start engine and raise engine speed. Check the EGR valve diaphragm and ensure there is no movement,

CAUTION: If EGR valve is hot, it may be necessary to wear gloves to avoid burning fingers.

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:

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

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

EGR Pressure Transducer Filter:

EGR MODULATOR

INSPECT:

^ Filter for contamination and damage (Clean filter, using compressed air.)
^ Remove EGR modulator and plug nozzle with your finger. Blow air into another nozzle and check that air passes through to air filter side.
^ Connect vacuum pump to nozzle "P" and plug nozzle "Q" with your finger. While blowing air into nozzle "A," operate vacuum pump and check that vacuum is applied to modulator.
^ If the modulator fails any of the previous tests, then it is defective and should be replaced. after replacement perform the test again to verify the repair.

Chart C-7 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.

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

1. This test checks that the EGR valve is mechanically functional. Be sure to check hoses for proper vacuum supply, plugged, kinked or deteriorated hoses.

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.