Exhaust Gas Recirculation (EGR) System Check

Chart C-7:

EGR Wiring Diagram:

EGR SYSTEM CHECK

CIRCUIT DESCRIPTION:

The digital EGR valve is designed to accurately supply exhaust gas to the engine without the use of manifold vacuum. The valve controls exhaust gas flow from the exhaust system to the intake manifold through two orifices. When the solenoid is energized, the armature, combined with an attached shaft and swivel pintle, is raised and the orifice is opened.
The flow accuracy is dependent on the orifice size only, which results in improved EGR control.




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

1. Trouble Codes should be diagnosed using appropriate charts (see COMPUTERIZED ENGINE CONTROLS section) before performing a functional check.
2. This step actuates each solenoid and should result in a momentary drop in speed or engine roughness of the EGR flows at idle. There should be more effect from the #2 solenoid than the #1 solenoid.

NOTE:

In the preceding test, the scan tool is grounding each EGR solenoid individually through a quad driver circuit in the ECM. Grounding the solenoids will open the passage and cause a drop in engine speed.

CAUTION: Not all "SCAN" testers are compatible with every system. A "SCAN" tool that produces faulty readings should NOT be used, and the problem should be reported to the tool manufacturer. Use of a faulty "SCAN" tool can result in improper diagnosis and unnecessary component replacement. Follow the proper instructions, located in the owners manual, for the specific "SCAN" tool be used.



INCORRECT EGR OPERATION:

1. If too much EGR is flowing at idle, cruise, or cold operation,
any of the following conditions could exist:
a. The engine dies after cold start.
b. The engine stalls on deceleration.
c. The vehicle surges during cruise mode.
d. Rough idle.

2. If too little or no exhaust gases flow, the combustion chamber temperature may increase under acceleration or heavy load conditions. These conditions could cause:
a. Detonation (Spark Knock).
b. The engine to overheat.
c. The emissions test to fail.