Part 1 of 2

Chart C-7 (Part 1 Of 2):

Exhaust Gas Recirculation (EGR) System Check (Part 1 Of 2):

CIRCUIT DESCRIPTION
The Exhaust Gas Recirculation (EGR) system is controlled by the Powertrain Control Module (PCM). The PCM controls vacuum being supplied to the EGR 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 engine operating conditions are indicated, a Diagnostic Trouble Code (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 solenoid control valve "ON" and allow vacuum to be applied to the gauge. 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 EGR valve is commanded "OFF," the vacuum gage should bleed off completely through a vent in the solenoid. The vacuum 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 up to the solenoid is functioning properly.
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 Emission Control Information Label. Emission Control Information Label
^ Also check vacuum lines for cracking, chafing, or breaks, replace as necessary.