EGR System Failure

WHEN MONITORED
Engine temperature greater than 180°F
Engine in closed loop
Oxygen sensor operational
Engine under a steady load with the throttle open
Adaptive memory NOT at or near its limits

SET CONDITION
When all the above conditions are met, the PCM turns the EGR solenoid off and on momentarily while monitoring the oxygen sensor output voltage.

- If no significant change is seen, a flag is set.
- This test is repeated up to 8 times in a run cycle.
- If the system fails the test every time for that run cycle, a trouble code is set.
- If the system passes the test at least once during a run cycle, the diagnostics are suspended for that run cycle.

THEORY OF OPERATION
The EGR system recirculates exhaust gases back through the intake manifold to help control combustion temperature and promote even flame distribution in the cylinder.

- This reduces NOx emissions and prevents spark knock.

- The EGR valve is controlled by manifold vacuum and exhaust backpressure through a solenoid/transducer.

- The PCM controls the solenoid operation through cavity 35.

PROBABLE CAUSES
- Open or Blocked Vacuum Supply To The EGR Valve
- Blocked Exhaust Transfer Tubes To The Intake Manifold
- Blocked Backpressure Tube To The Transducer
- Failed EGR Valve
- Failed EGR Solenoid/Transducer
- Failed PCM