Main Relay (Computer/Fuel System): Testing and Inspection

POWERTRAIN RELAY DIAGNOSIS

CIRCUIT DESCRIPTION
The powertrain relay is a normally open relay. The relay armature is held in the open position by spring tension. Battery positive voltage is supplied directly to the relay coil and the armature contact at all times. The powertrain control module (PCM) supplies the ground path to the relay coil control circuit, via an internal integrated circuit called an output driver module (ODM). When the PCM commands the relay ON, the relay coil creates an electromagnetic field. This electromagnetic field overcomes the spring tension and pulls the armature contact into the stationary contact of the relay load circuit. The closing of the relay contacts allows current to flow from the battery to the following fuses:
- ETC FUSE
- O2 SENSOR FUSE

When the ignition switch is turned to the OFF position, the powertrain relay will continue to be energized for 5 seconds after the key is turned OFF. Once the power is interrupted to the output driver module in the PCM, the relay electromagnetic field collapses. This allows the spring tension to separate the relay armature contact from the relay load circuit contact, which interrupts current flow to the fuses.

If the powertrain relay fails to close the engine will crank, but will not run. The PCM class 2 communications will be available with the use of a scan tool.

The powertrain relay system diagnosis table assumes that the vehicle battery if fully charged. Refer to Battery Inspection/Test (Non-HP2) in Starting and Charging. Battery Inspection/Test

TEST

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