How long does the main relay (computer/fuel system) last?

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1. Periodically does not scroll or start.
2. Engine won't crank or won't start at all

The host computer relay is responsible for supplying power to the powertrain control module (PCM). The PCM is the main computer that controls the operation of the engine, transmission, emission control system, starting system and charging system. Other systems not directly related to emissions control the PCM to varying degrees.

When the PCM relay starts to fail, several symptoms are possible.

1. Periodically does not scroll or start.

The relay may fail intermittently. This creates conditions under which the engine may crank but not start. It may also prevent the engine from starting. The PCM has no power to supply power to the fuel injection system and the ignition system, resulting in an inability to start. The rest of the time the engine starts and runs normally. The most common cause of intermittent relay failure is an open circuit within the relay itself, usually due to open solder joints.

2. Engine won't crank or won't start at all

When the PCM relay has completely failed, the engine will either not start or will not start at all. However, PCM is not the only possible reason for the lack of startup/startup. Only a trained technician, such as at AvtoTachki, will be able to determine what the true cause is.

A faulty PCM relay will prevent the PCM from turning on. When this happens, the PCM will not be able to communicate with any diagnostic scanner. For the technician, the lack of communication with the PCM complicates the diagnosis.

If the relay fails, it must be replaced.