EGR System Diagnosis

Circuit Description
An Exhaust Gas Recirculation (EGR) system is used to lower Oxides of Nitrogen (NOx) emission levels caused by high combustion temperatures. It accomplishes this by feeding small amounts of exhaust gases back into the combustion chamber. When the air/fuel mixture is diluted with the exhaust gases, combustion temperatures are reduced.

A linear EGR valve is used on this system. The linear EGR valve is designed to accurately supply exhaust gases to the engine without the use of intake manifold vacuum. The valve controls exhaust flow going into the intake manifold from the exhaust manifold through an orifice with a Control Module (PCM/VCM) controlled pintle valve. The Control Module commands the EGR by applying a 12 volt duty cycle to the EGR valve. This can be monitored on a scan tool as Desired EGR position.

The Control Module can monitor the pintle position with the EGR pintle position signal. This sensor uses a variable resistor with a 5 volt reference, a signal circuit and a ground. The signal circuit monitors changes in voltage on the variable resistor as the pintle moves.

An intermittent may be caused by any of the following conditions:
^ A poor connection
^ Rubbed through wire insulation
^ A broken wire inside the insulation

Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis. Symptom Related Diagnostic Procedures

Test Description
The numbers below refer to the step numbers in the diagnostic table.
2. At idle the EGR valve should not be open greater than 0%.
3. This step checks the ability of the pintle to be manually commanded to the desired positions.
5. This step checks the electrical circuit for a short to voltage.
6. This step checks the electrical control circuits from the VCM to the EGR valve.