Main Relay (Computer/Fuel System): Description and Operation

PRINCIPLE OF OPERATION, MAIN RELAY

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Main Relay--is located in the relay holder on the passenger side.

The relay supplies the injectors, ignition discharge module, idle air control valve and evaporative emission canister purge valve with current. The main relay is controlled from pin 31 of the control module which is grounded for the relay to operate.

If the engine is started and the ignition then switched off for more than 45 seconds, the main relay will operate for about 6 seconds to allow for pre-injection next time the ignition is switched on. On the other hand, if the ignition is switched on without the engine being started, pre-injection will not take place again unless the ignition has been switched off for 15 minutes.

The main relay then operates as soon as the control module receives pulses from the crankshaft position sensor.

When the engine is switched off the main relay will continue to operate for about 6 seconds. This is in order to supply the ignition discharge module with current for spark plug burn-off.