The Exhaust Gas Recirculation (EGR) system is used to reduce Oxides of Nitrogen (NOx) emission levels caused by high combustion chamber temperatures. It does this by decreasing combustion temperature. The main element of this system is the linear EGR valve. The EGR valve feeds small amounts of exhaust gas back into the combustion chamber. With the fuel/air mix thus diluted, combustion temperatures are reduced.
The linear EGR valve, used on the vehicles covered by this guide, is designed to accurately supply EGR to an engine independent of intake manifold vacuum. The valve controls EGR flow from the exhaust to the intake manifold through an orifice with a PCM controlled pintle. During operation, the PCM controls pintle position by monitoring the pintle position feedback signal. The PCM uses information from the Engine Coolant Temperature (ECT) sensor, Throttle Position (TP) sensor and Mass Air Flow (MAF) sensor to determine the appropriate rate of flow for a particular engine operating condition.
A technician with a scan tool can monitor the feedback signal. The reading on the scan tool is ACTUAL EGR POS. which should always be near the commanded EGR position (DESIRED EGR POS). If a problem with the EGR system will not allow the PCM to control pintle position properly, a DTC should set. The PCM also tests for EGR flow. If flow is incorrect, a DTC should set.
A scan tool is required to retrieve DTCs and monitor the EGR system. The testing a non-professional can reasonably perform is limited to visual checks.
If the EGR valve shows signs of excessive heat, check the exhaust system for blockage (possibly a plugged catalytic converter). The following should also be checked:
- Remove the EGR valve and look for excessive deposits on the EGR pintle or seat. Check for deposits that may interfere with the EGR valve pintle extending completely or cause the pintle to stick.
- Look for a poor connection or damaged harness. Inspect the wiring harness for damage. If the harness appears to be okay, a scan tool will be required to observe the EGR actual position display while moving the wiring and harness, trying to locate and intermittent wiring fault.
REMOVAL & INSTALLATION
- Disconnect the negative battery cable.
- Detach the electrical connector from the EGR valve.
- On the 3.5L (VIN H) engine, remove the fuel lines from the EGR valve bracket.
- Remove the two base-to-flange nuts (or bolts) and lift the EGR valve assembly from the vehicle. Discard the gasket.
- Take the time to thoroughly clean the gasket sealing surfaces to avoid raw exhaust gas leaks
- Installation the reverse of removal. Always use a new gasket and torque the retaining fasteners to 22 ft. lbs. (30 Nm).
- Verify the electrical connector is secure.
- Connect the negative battery cable.