| CAUTION | If ECM replacement is instructed in following testing, always ensure ECM harness connector and ground circuit are okay. If either are suspect, repair and repeat testing to confirm ECM malfunction. |
Circuit Description
The EGR system recirculates exhaust gas through intake system to reduce combustion temperature and NOx emissions. The amount of EGR valve opening is controlled by a stepper motor located inside of EGR valve. The ECM operates the step motor in response to engine operating conditions.
The EGR valve is closed under the following conditions
- Coolant temperature less than 129°F (54°C).
- Vehicle under deceleration.
- Light engine load.
- Engine speed more than 4000 RPM.
- Engine idling.
- Park/neutral position switch on.
DTC is set when EGR temperature sensor value does not exceed 86°F (30°C) more than ambient air temperature after vehicle is operated for 3-5 minutes at 50 MPH or more. Possible causes are
- EGR valve.
- EGR temperature sensor open circuit.
- EGR stepper motor circuit.
- ECM.