Exhaust Gas Recirculation: Testing and Inspection

EGR System Check:

Exhaust Gas Recirculation (EGR) Valve Vacuum Solenoid Circuit Diagram:

CIRCUIT DESCRIPTION
The EGR valve is controlled by a normally closed solenoid. The PCM turns the solenoid "ON" to allow vacuum to pass to the EGR, and turns the solenoid "OFF" to prevent EGR operation.

The duty cycle is calculated by the PCM based on information from the CTS, IAT, TPS and MAP sensors as well as engine rpm and P/N switch input. There should be no EGR when in park or neutral, TPS below a calibrated value or TPS indicating WOT.

With ignition "ON" and engine "OFF", the EGR solenoid is de-energized. The solenoid, however, should be energized, if the diagnostic "test" terminal is grounded with the ignition "ON" and engine "OFF".



TEST DESCRIPTION (PART 1)
Numbers below refer to circled numbers on the diagnostic chart.
1a. INTAKE PASSAGE: Shut "OFF" engine and remove the EGR valve from the manifold. Plug the exhaust side hole with a shop rag or suitable stopper. Leaving the intake side hole open, attempt to start the engine. If the engine runs at a very high idle (up to 3000 rpm is possible) or starts and stalls, the EGR passages are not restricted. If the engine starts and idles normally, the EGR intake side passage in the intake manifold is restricted.
1b. EXHAUST PASSAGE: With EGR valve still removed, plug the intake side hole with a suitable stopper. With the exhaust side hole open, check for the presence of exhaust gas. If no exhaust gas is present, the EGR exhaust side passage in the intake manifold is restricted.

2. The vacuum at the gage may or may not slowly bleed off. It is important that the gage is able to read the amount of vacuum being applied.

3. When the diagnostic "test" terminal is grounded the vacuum gage should bleed off through a vent in the solenoid. The pump gage may or may not bleed off but this does not indicate a problem.

4. This test will determine if the electrical control part of the system is at fault or if the connector solenoid is at fault.

DIAGNOSTIC AIDS
Vacuum lines should be thoroughly checked for proper routing. Refer to "Vehicle Emission Control Information" label.

Suction from shop exhaust hoses can alter backpressure and may affect the functional check of the EGR valve.


TEST DESCRIPTION (PART 2)
Numbers below refer to circled numbers on the diagnostic chart.

1. The remaining test checks the ability of the EGR valve to interact with the exhaust system. This system uses a negative backpressure EGR valve which should hold vacuum with engine "OFF".

2. When engine is started, exhaust backpressure at the base of the EGR valve should open the valve's internal bleed and vent the applied vacuum allowing the valve to seat.

DIAGNOSTIC AIDS
Suction from shop exhaust hoses can alter backpressure and may affect the functional check of the EGR valve.

During normal EGR valve operation, the movement of the EGR pintle is small. It is important to determine whether the valve pintle moves and not how much it moves.