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 engine control module (ECM) supplies the ground path to the relay coil control circuit via an internal integrated circuit, called an output driver module (ODM). One ODM output control is configured to operate as a low side driver for the main relay. The low side driver for the main relay also incorporates a fault detection circuit, which is continuously monitored by the ECM. DTC P0686 indicates an open, high resistance, or a short to ground in the main relay coil control circuit. If the fault detection circuit measures a low voltage condition, DTC P0686 will set.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0686 Engine Controls Ignition Relay Control Circuit
Conditions for Running the DTC
| • | The battery voltage is between 9-16 volts. |
| • | The ignition switch is turned ON. |
| • | DTC P0686 runs continuously once the above conditions are met. |
Conditions for Setting the DTC
| • | The ECM detects a lower than expected voltage on the relay coil control circuit. |
| • | The condition is present for more than 200 milliseconds. |
Action Taken When the DTC Sets
| • | The control module stores the DTC information into memory when the diagnostic runs and fails. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records. |
| • | The driver information center, if equipped, may display a message. |
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 main relay will remain powered up for 15 seconds after the ignition switch is turned OFF. |
| • | This DTC diagnostic table assumes that the vehicle battery is fully charged. Refer to Battery Inspection/Test in Engine Electrical. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The engine will crank and run, with a short to ground on the main relay coil control circuit. This condition could result in a discharged battery.
-
The engine will crank but will not run, with a high resistance or an open on the main relay coil control circuit.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module Connector End Views and Engine Controls Connector End Views | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
2 |
Did the DTC fail this ignition? | -- | Go to Step 3 | Go to Intermittent Conditions |
Attempt to start the engine. Does the engine start and run? | -- | Go to Step 6 | Go to Step 4 | |
4 |
Notice: Refer to Test Probe Notice in the Preface section. Does the test lamp illuminate? | -- | Go to Step 5 | Go to Step 10 |
Does the test lamp illuminate? | -- | Go to Step 9 | Go to Step 17 | |
6 |
Notice: Refer to Test Probe Notice in the Preface section. Does the test lamp illuminate? | -- | Go to Step 7 | Go to Step 11 |
7 |
Notice: Refer to Test Probe Notice in the Preface section. Does the test lamp illuminate? | -- | Go to Step 8 | Go to Step 13 |
8 |
Does the test lamp illuminate? | -- | Go to Step 14 | Go to Step 19 |
9 |
Does the resistance measure greater than the specified value? | 5 ohms | Go to Step 17 | Go to Step 11 |
10 | Probe the mounting stud for the battery positive cable at the underhood fuse block with a test lamp that is connected to a good ground. Does the test lamp illuminate? | -- | Go to Step 19 | Go to Step 15 |
11 | Measure the resistance from terminal #85 of the main relay to terminal #86 with a DMM. Refer to Troubleshooting with a Digital Multimeter in Wiring Systems. Does the resistance measure within the specified range? | 70-110 ohms | Go to Step 12 | Go to Step 18 |
12 | Test for an intermittent and for a poor connection at the main relay location of the underhood fuse block. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find a condition? | -- | Go to Step 19 | Go to Step 13 |
13 | Test for shorted terminals and poor connections at the ECM electrical connectors. Refer to Testing for Intermittent Conditions and Poor Connections and Micro .64 Connectors in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 21 | Go to Step 20 |
14 | Repair the short to ground in the main relay coil control circuit between the underhood fuse block electrical connector and the ECM electrical connector. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 21 | -- |
15 | Test for an intermittent and for a poor connection in the battery positive cable between the underhood fuse block and the battery. Did you find and correct the condition? | Go to Step 21 | Go to Step 16 | |
16 | Replace the battery positive cable to the underhood fuse block. Refer to Battery Positive Cable Replacement in Engine Electrical. Did you complete the replacement? | Go to Step 21 | -- | |
17 | Repair the high resistance or an open in the main relay coil control circuit between the underhood fuse block electrical connector and the ECM electrical connector. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 21 | -- |
18 | Replace the main relay. Refer to Relay Replacement in Wiring Systems. Did you complete the replacement? | -- | Go to Step 21 | -- |
19 | Replace the underhood fuse block. Refer to Underhood Electrical Center or Junction Block Replacement in Wiring Systems. Did you complete the replacement? | -- | Go to Step 21 | -- |
20 | Replace the ECM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 21 | -- |
21 |
Did the DTC fail this ignition? | -- | Go to Step 3 | Go to Step 22 |
22 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | System OK |
