Part 1 of 3

EGR Testing Part 1 Of 3:

EGR Wiring Diagram:

CIRCUIT DESCRIPTION:

The ECM operates a vacuum solenoid to control the EGR valve. The solenoid is normally closed. The ECM provides a ground path to energize the solenoid. This allows vacuum to flow to the EGR valve.

The ECM control of the EGR valve is based on the following inputs;

^ Engine coolant temperature above 25°F
^ TPS off idle
^ MAP
^ If code 24 is stored use that chart first


TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

1. Intake Passage: Shut "OFF" the engine and remove the EGR valve from the manifold. Plug the exhaust side hole with a shop towel or suitable stopper. Leaving the intake hole open, attempt to start the engine. If the engine runs at a very high idle speed (up to 3000 rpm is possible) or starts and stalls, the EGR passages are not restricted. If the engine starts and idles normal, the EGR intake side passage, in the intake manifold, is restricted.
Exhaust Passage: With the EGR valve still removed, plug the intake side hole with the same 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.
NOTE: Remove towel or stopper once test is complete.

2. Grounding the diagnostic test terminal should allow the EGR solenoid to energize, and vacuum should flow to the gauge. The vacuum at the gauge may or may not bleed off slowly.

It is important that the gage is able to read the amount of vacuum being applied.

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

4. This test determines if the electrical control portion of the system is at fault, or if the EGR solenoid and/or connector is at fault.

5. EGR valves used with this engine are stamped "P" for Positive and "N" for Negative. See EMISSION CONTROLS, for "EGR IDENTIFICATION," under COMPONENT OPERATION, to assist in determining the type of EGR valve used.



DIAGNOSTIC AIDS:

^ Vacuum hoses should be thoroughly inspected for proper routing.