Symptoms of a Bad or Failing Electronic Control Relay

The electronic control relay, also known as the “main” relay, is one of the various electronic relays found on modern vehicles. The electronic control relay is particularly important, as it is one of the main relays that feeds power to the computer, which controls a vast majority of the vehicle’s functions. As the electronic control relay powers the computer, when it fails it can cause all sorts of issues with the vehicle. Usually a bad or failing electronic control relay will produce a few symptoms that can alert the driver of a potential issue that should be serviced.

Engine cranks but does not start

One of the most common symptoms of a problem with the electronic control relay is an engine that cranks but does not start. If the relay has any sort of issue it may compromise power to the computer, which will not allow the vehicle to start. For many vehicles the engine’s starting circuit is on a separate circuit and relay than the computer’s, so the engine will still crank even if the computer relay has failed.

Vehicle that powers on but does not function

Another symptom of a bad or failing electronic control relay is a vehicle that powers on when the key is inserted, but does not function. For some vehicles, the vast majority of the vehicle’s relays are powered by the computer, so any issue with the relay or computer may cause a problem with all of the electronic circuits on the vehicle powered through the computer. A vehicle with no power when the key is inserted will be rendered undriveable until the relay is replaced.

The electronic control relay is a critical relay to any vehicle, as it is what supplies power to the computer, one of the most important electronic components found on modern vehicles. When it fails, the functionality and driveability of the vehicle can be greatly affected. If you suspect that your electronic control relay may be having an issue, have the vehicle inspected by a professional technician, such as one from YourMechanic to determine if your car needs a relay replacement.


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