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Exhaust gas recirculation, or EGR, was introduced decades ago to minimize a vehicle’s environmental impact and cool the intake temperature by introducing inert gases into the combustion process. It was quickly discovered that when the engine was cold, the EGR system caused a rough run condition and the engine could stall or hesitate. The correction was a vacuum switch. Mounted on the intake manifold, an override switch detected the engine coolant temperature and would not allow vacuum supply to the EGR system until the engine reached a certain temperature, usually around 100 degrees Farenheit. When the coolant warmed up sufficiently, an internal valve in the switch would change position and allow vacuum to pass through.
This simple switch allows the engine to run smoothly at cold temperatures and enhances performance through all temperature ranges. If the override switch does not operate as it should and allows vacuum even in cold temperatures, you will experience a rough run, hesitation to accelerate, and a stalled engine. If the switch remains closed after the engine temperature reaches operating temperature, you will experience an engine knock. EGR codes will cause the Check Engine light to come on.
The EGR coolant temperature override switch is unlikely to require replacement in the life of your vehicle unless it becomes plugged by debris. If you suspect an EGR system malfunction, have it checked by one of our expert technicians and repaired as necessary.
If your EGR coolant temperature override switch fails, you will experience unreliable engine operation and possible engine damage if it's left unattended. Have the EGR coolant temperature override sensor replaced as soon as possible once it fails.