| 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 regulated by the EGR vacuum modulator according to engine load. Vacuum source to valve is controlled by the Vacuum Switching Valve (VSV), which is operated by ECM.
The EGR valve is closed (VSV on) under the following conditions
- Coolant temperature less than 140°F (60°C).
- Vehicle under deceleration.
- Light engine load.
- Engine racing.
DTC is set when EGR gas temperature sensor value is high during EGR cut-off when engine is cold, or if EGR valve is always open. Possible causes are
- EGR valve stuck open.
- VSV open circuit.
- EGR gas temperature sensor short circuit.
- ECM.