Exhaust Gas Recirculation: Testing and Inspection

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 ECT, MAF and RPM. There should be no EGR when in park or neutral, TP below a calibrated value or TP 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".

EGR System Check:

EGR Control Circuit:

Test 1 Description
Numbers below refer to circled numbers on the diagnostic chart.
1. 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.
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 gauge may or may not slowly bleed off. It is important that the gauge is able to read the amount of vacuum being applied.

3. When the output/field service enable terminal is grounded, or Tech 1 is used, the vacuum gauge should bleed off through a vent in the solenoid valve. The pump gauge may or may not bleed off but this does not indicate a problem.

Diagnostic Aids
Suction from shop exhaust hoses can alter backpressure and may affect the operation of the EGR valve during in stall testing. An exhaust leak will alter backpressure. Throughly check exhaust system for leaks.
Vacuum lines should be thoroughly checked for proper routing. Vacuum source goes to orifice side of the solenoid valve. Refer to "Vehicle Emissions Control Information" Label.

Chart C-7 (2 of 2):

Test 2 Description
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.
When the transmission enables TCC the EGR will be in a reduced duty cycle.