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 MIL operation.
Diagnostic Aids
Use the Connector Test Adapter Kit J 35616 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 Engine Control Module Diagnosis , Checking Terminal Contact, for the proper procedure.
Refer to Symptoms for the Intermittents.
Test Description
The number(s) below refer to the step numbers on the diagnostic table.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System check? | -- | ||
2 |
Does the test light illuminate? | -- | ||
3 |
Does the test light illuminate on both circuits? | -- | ||
4 |
Does the test light illuminate? | -- | ||
5 |
Is continuity indicated? | -- | ||
Repair the battery feed circuit. Is the action complete? | -- | -- | ||
7 | Repair the open/high resistance switched B+ circuit. Is the action complete? | -- | -- | |
8 | Check for any poor connections at the relay. Was a problem found and corrected? | -- | ||
9 | Replace the relay. Is the action complete? | -- | -- | |
10 | Repair the open/high resistance relay control circuit. Is the action complete? | -- | -- | |
11 | Check for a poor connection or poor terminal tension at the ECM harness connector. Refer to Electrical Diagnosis in Engine Electrical, and Troubleshooting Procedures for the proper procedure. Also, refer to Checking Terminal Contact in Engine Control Module Diagnosis . Was a problem found and corrected? | -- | ||
12 |
Important: This vehicle is equipped with a Theft Deterrent System which interfaces with the Engine Control Module (ECM). Program the new ECM with the frequency code of the theft deterrent module that is currently on the vehicle. Replace the ECM. Refer to Engine Control Module Replacement/Programming . Is the action complete? | -- | -- | |
13 |
Does the engine start and continue to run? | -- | ||
14 |
Are there any DTCs displayed? | -- | Go to the applicable DTC table | |
15 | Were there any additional DTCs noted during the Powertrain OBD System Check that have not been diagnosed? | -- | Go to the applicable DTC table | The System is OK |
