Chart C-7 EGR System Check

Chart C-7: Part 1 Of 3:

Chart C-7: Part 2 Of 3:

Chart C-7: Chart 3 Of 3:

EGR Solenoid Valve:

CIRCUIT DESCRIPTION
The Engine Control Module (ECM) operates a solenoid to control the Exhaust Gas Recirculation (EGR) valve. This solenoid is normally closed. By providing a ground path, the ECM energizes the solenoid which then allows vacuum to pass to the EGR valve. The ECM control of the EGR is based on the following inputs:

^ Engine coolant temperature - above 25°C
^ Throttle Position (TP) sensor - "OFF" idle
^ Manifold Absolute Pressure (MAP)

If Code 24 is stored, refer to that chart first. Powertrain Controls - ECM/PCM

TEST DESCRIPTION
Numbers below refer to circled numbers on diagnostic chart part 1 of 3.

(Part 1 of 3)
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. By grounding the diagnostic "test" terminal, the EGR solenoid valve should be energized and allow vacuum to be applied to the gage. 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 ungrounded, the vacuum gage should bleed off through a vent in the solenoid valve. 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 or solenoid valve is at fault.

5. EGR valves used with this engine are stamped on the top side of the valve with: (P) for Positive backpressure valves or (N) for Negative backpressure valves. Refer to EGR Valve/Application and ID for more information. EGR Valve

DIAGNOSTIC AIDS
Vacuum lines should be thoroughly checked for proper routing. Vacuum source goes to orifice side of the EGR solenoid valve. Refer to the underhood "Vehicle Emission Control Information" label. Emission Control Information Label

TEST DESCRIPTION
Numbers below refer to circled numbers on diagnostic chart part 2 of 3.

(Part 2 of 3)
6. The remaining tests check the ability of the EGR valve to interact with the exhaust system. This system uses a positive backpressure EGR valve which will not hold vacuum until sufficient exhaust backpressure is at the base of the valve.

7. The EGR valve diaphragm should move when sufficient exhaust backpressure is present at the base of the valve and when vacuum is being supplied to the valve. Rapidly "snapping" the throttle from idle should provide sufficient exhaust backpressure to the base of the valve which will close an internal vacuum bleed. With the EGR valve's internal vacuum bleed closed, the vacuum supply can now lift the valve off its seat.

8. Excessive exhaust backpressure from bent or restricted exhaust system components could provide enough backpressure at the base of the EGR valve to close the valve's internal bleed and allow undesired EGR valve operation at idle.

9. Plugged EGR exhaust passages can block exhaust backpressure from reaching the EGR valve. With no EGR exhaust backpressure at the base of the valve, the valve's internal bleed will remain open and prevent vacuum from operating the valve.

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

TEST DESCRIPTION
Numbers below refer to circled numbers on diagnostic chart part 3 of 3.

(Part 3 of 3)
10. The remaining tests check 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."

11. 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.