Circuit Diagnosis - Power Relay

Diagnostic Chart:

Diagram Chart:

Electrical:

CIRCUIT DESCRIPTION

The Engine Controls Power Relay's Coil and contacts are connected directly to the battery positive voltage (B+). The Engine Control Module (ECM) controls the relay by grounding the control circuit via an internal solid state device called a driver. When the ECM detects a voltage on the ignition feed circuit, the ECM enables the Engine Controls Power Relay. The Engine Controls Power Relay controls the Switched B+ circuit to the IAC valve, the Fuel Pump relay coil, the fuel injectors, the HO2S heaters and the other various engine control components which use a switched B+ supply. The ECM also uses the Switched B+ circuit to power up a portion of itself, including the circuitry which controls the Malfunction Indicator Lamp (MIL) operation.

DIAGNOSTIC AIDS

Use the Connector Test Adapter Kit J 35616-A for any test that requires probing the ECM harness connector or a component harness connector. Using this kit will prevent damage to the harness connector terminals.

Check for poor connections at the ECM or at the component. Inspect the harness connectors for any of the following conditions:

^ Backed out terminals

^ Improper mating

^ Broken locks

^ Improperly formed or damaged terminals

^ Poor terminal to wire connection

Refer to Overall Vehicle Information / Diagrams / Diagnostic Aids Checking Terminal Contact procedure.

Refer to Symptoms / Intermittents. Testing and Inspection

TEST DESCRIPTION

The number(s) below refer to the step numbers on the diagnostic table.

6. Check the battery feed circuit for an open circuit or a short to ground. If an open fuse is found, the following conditions may have caused the fuse for the Engine Controls Power Relay battery feed to open:

^ The fuse was damaged, corroded, or malfunctioning.

^ There is an intermittent short in one of the circuits tested in this table. Moving the harness and any of the related connectors with the system operating may uncover an intermittent short to ground.

^ A component which is powered by the switched B+ circuit has an intermittent internal problem.