Circuit Description
The main 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). One of the ODM output circuits is configured to operate as a low side driver for the main relay. The low side driver also incorporates a fault detection circuit, which is continuously monitored by the PCM. When the PCM commands the relay ON, the expected voltage on the relay coil control circuit should be a low voltage condition. If the fault detection circuit measures a high voltage condition, DTC P0685 will set. DTC P0685 indicates a short to battery positive voltage, or ignition 1 voltage on the main relay control circuit.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0685 Engine Controls Ignition Relay Control Circuit
Conditions for Running the DTC
| • | The battery voltage is between 11.0 and 18.0 volts |
| • | The ignition is ON. |
| • | The diagnostic runs continuously when the above conditions are met. |
Conditions for Setting the DTC
The PCM detects more than 4.6 volts on the relay coil control circuit for more than 2 seconds.
Action Taken When the DTC Sets
| • | The PCM will not illuminate the malfunction indicator lamp (MIL) if this diagnostic runs and fails. |
| • | The engine will crank, but will not run. |
| • | The Class II communications will be available with the use of a scan tool. |
| • | The engine will crank, but will not run, or the engine will crank and run in reduced power mode. |
| • | The class II communications will be available with the use of a scan tool. |
| • | The PCM sets the code and turns OFF the ODM for PCM protection. |
Conditions for Clearing the DTC
| • | A current DTC Last Test Failed clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic. |
| • | Clear the DTC with a scan tool. |
Diagnostic Aids
The P0685 diagnostic table assumes that the vehicle battery is fully charged. Refer to Battery Inspection/Test in Engine Electrical.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics and Power Distribution Schematics in Wiring Systems Connector End View Reference: Engine Controls Connector End Views and Electrical Center Identification Views in Wiring Systems | ||||
1 | Did you perform the Diagnostic System Check - Vehicle | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
2 |
Notice: Refer to Test Probe Notice in the Preface section. Does the test lamp illuminate? | -- | Go to Step 6 | Go to Step 3 |
3 |
Does the test lamp illuminate? | -- | Go to Step 4 | Go to Step 8 |
4 |
Does the test lamp illuminate? | -- | Go to Step 5 | Go to Step 11 |
5 |
Does the test lamp illuminate? | -- | Go to Step 12 | Go to Step 14 |
6 |
Does the test lamp illuminate? | -- | Go to Step 7 | Go to Step 11 |
7 |
Does the test lamp illuminate? | -- | Go to Step 12 | Go to Step 14 |
8 | Measure the resistance from terminal 30 of the relay to terminal 85 with a DMM. Refer to Troubleshooting with a Test Lamp in Wiring Systems. Does the DMM display the specified value? | ∞ ohms | Go to Step 9 | Go to Step 13 |
9 | Measure the resistance from terminal 85 of the relay to terminal 87 with a DMM. Does the DMM display the specified value? | ∞ ohms | Go to Step 10 | Go to Step 13 |
10 | Measure the resistance from terminal 85 of the relay to terminal 86 with a DMM. Does the DMM display the specified value? | 70-110 ohms | Go to Step 16 | Go to Step 13 |
11 | Test for shorted terminals and poor connections at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Delphi Connectors in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 15 |
12 | Repair the short to voltage in the main relay coil control circuit between the underhood junction block electrical connector and the PCM electrical connector. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 16 | -- |
13 | Replace the main relay. Refer to Relay Replacement in Wiring Systems. Did you complete the replacement? | -- | Go to Step 16 | -- |
14 | Replace the underhood junction block. Refer to Underhood Electrical Center or Junction Block Replacement in Wiring Systems. Did you complete the replacement? | -- | Go to Step 16 | -- |
15 | Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 16 | -- |
16 |
Does the engine start and run? | -- | Go to Step 17 | |
17 |
Does the DTC set during this ignition cycle? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | System OK |
