Part 1 of 2

Chart C-7 EGR System Check (Part 1 Of 2):

EGR Solenoid Wiring Circuit:

Circuit Description:
The Exhaust Gas Recirculation (EGR) system is controlled by the PCM. The PCM controls the vacuum being supplied to the valve by energizing and de-energizing a solenoid.

The PCM uses information from various engine sensors to determine when EGR is necessary. Once the PCM has requested EGR by grounding the solenoid circuit, the PCM will monitor engine operating conditions to determine if exhaust gas flow has entered the intake manifold. When the PCM tests for EGR operation and no change in MAP is indicated, a DTC will set.

Chart Test Description: Number(s) below refer to circled number(s) 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 suitable stopper. Leaving the intake side hole open, attempt to start the engine. If the engine runs at a high idle (up to 3000 RPM is possible) or starts and stalls, the EGR intake passage is not restricted. If the engine starts and idles normally, the EGR intake passage 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 is restricted.

2. By using "Misc Test" function on the Tech 1, command the EGR valve 'ON" 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 EGR valve is commanded "OFF," the vacuum gage should bleed off completely through a vent in the solenoid. The vacuum 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.
5. At this point, it has been determined that the EGR control solenoid valve, the PCM and the vacuum supply are OK.

Diagnostic Aids: Vacuum lines should be thoroughly checked for proper routing. Refer to "Vehicle Emission Control Information" label.

Also check vacuum lines for cracking, chafing, or breaks.