Engine Controls Power Relay Circuit Diagnosis

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 through 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 fuel pump relay coil, the fuel injectors, the HO2S heaters and the other engine control components that 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 MIL operation.

Diagnostic Aids

Notice: Refer to J35616-A Connector Test Adapter Kit Notice in Service Precautions.

Use the J 35616-A connector test adapter kit for any test that requires probing the ECM harness connector or a component harness connector.

Intermittent connections may cause the engine to stall or an intermittent loss of communication. Loss of the switched B+ voltage may cause multiple DTCs to set.

Check for faulty connections at the ECM or at the component. Check all other circuits that are spliced to the engine controls power relay for the proper operation. 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 Symptoms for the Intermittents. Symptom Related Diagnostic Procedures

Test Description
The numbers below refer to the step numbers on the diagnostic table.
15. This step is to verify the remaining circuits required to operate the ECM and the engine controls power relay.