Diagnostic Instructions

DTC Descriptor

DTC P0685: ECM Power Relay Control Circuit/Open

DTC P0689: ECM Power Relay Sense Circuit Low

DTC P0690: ECM Power Relay Sense Circuit High

Diagnostic Fault Information

Circuit	Short to Ground	High Resistance	Open	Short to Voltage	Signal Performance
B+ Reference Voltage - Coil	P0685	P0685	P0685	--	--
B+ Reference Voltage - Armature	P0689	P0689	P0689	--	--
Relay Control Circuit	P0685	P0685	P0685	P0685	--
Relay Feedback Circuit	P0689	P0689	P0689	P0690	--

Typical Scan Tool Data

EC Ignition Relay Feedback Signal

Circuit	Normal Range	Short to Ground	Open	Short to Voltage
Operating Conditions: Ignition ON, with the engine OFF.
B+ Reference Voltage - Coil	--	0.0 V	0.0 V	--
B+ Reference Voltage - Armature	--	0.0 V	0.0 V	--
EC Ignition Relay Control	--	0.0 V	0.0 V	--
EC Ignition Relay Feedback	11.9-12.9 V	0.0 V	0.0 V	More than 2 V¹
¹ DTC P0690 sets if the ECM detects voltage when the ignition is OFF.

Circuit/System Description

The power train 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). The ODM output control is configured to operate as a low side driver for the power train relay. The ODM for the power train relay also incorporates a fault detection circuit, which is continuously monitored by the ECM. When the ECM commands the power train relay ON, ignition 1 voltage is supplied to the following fuses and relays in the underhood fuse block:

The ignition 1 voltage that is supplied to the ECM through the ECM/throttle fuse, provides power to the internal ECM circuits associated with the throttle actuator control (TAC) operation. The ECM also monitors the voltage level on the ignition 1 voltage circuit to confirm that the power train relay contacts have closed.

Conditions for Running the DTC

DTC P0685 and DTC P0689

DTC P0690

Conditions for Setting the DTC

DTC P0685

DTC P0689

DTC P0690

Action Taken when the DTC Sets

DTCs P0685, P0689, or P0690 type B DTCs.

Conditions for Clearing the MIL/DTC

DTCs P0685, P0689, or P0690 type B DTCs.

Diagnostic Aids

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

Scan Tool Reference

Control Module References

Circuit/System Verification

1. Ignition ON, engine OFF, command the power train relay ON and OFF several times using the scan tool output control function. You should either hear or feel the relay click with each command.
2. Ignition ON, engine OFF, probe both test points of each of the following fuses. The test lamp should illuminate on at least one test point of each fuse.

•	The ENG 1 fuse

•	The ECM/throttle fuse

•	The INJ A fuse

•	The INJ B fuse

•	The O2A fuse

•	The O2B fuse

⇒

If the vehicle passes the Circuit/System Verification Test, then operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records Data List. Another option is to refer to Testing for Intermittent Conditions and Poor Connections .

Circuit/System Testing

1. Ignition OFF, remove the power train relay from the underhood fuse block.
2. Ignition ON, measure for battery positive voltage (B+) between the relay coil voltage supply circuit and a known ground.

⇒	If the voltage measures less than B+ repair the open/high resistance in the circuit to the relay coil. All wire circuit resistance should measure less than 2 ohms.

3. Measure for voltage between the relay coil control circuit and a known ground.

⇒	If voltage is measured on the control circuit of the relay, test for a short to voltage. If the circuit tests normal, replace the ECM.

4. Connect a test lamp between the B+ voltage supply circuit of the relay coil and the relay coil control circuit at the underhood fuse block. Use a scan tool to command the power train relay ON and OFF. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp stays ON all the time, test for a short to ground on the relay coil control circuit. If the circuit tests normal, replace the ECM.

⇒	If the test lamp stays OFF all the time, test for an open/high resistance on the relay coil control circuit. If the circuit tests normal, replace the ECM. All wire circuit resistance should measure less than 2 ohms.

5. Measure for B+ between the relay armature supply circuit and a known ground.

⇒	If the voltage measures less than B+, repair the open/high resistance in the circuit to the relay armature. All wire circuit resistance should measure less than 2 ohms.

6. Ignition ON, test for voltage on each test point of the ECM/throttle fuse in the underhood fuse block with a test lamp. For this test voltage should not be present at the ECM/throttle fuse.

⇒	If voltage is present, test the ignition 1 voltage circuit between the power train relay and the ECM for a short to voltage.

⇒	If both circuits test normal, replace the ECM.

7. Connect a 20-A fusible link wire between the B+ terminal and the ignition 1 voltage terminal of the power train relay at the underhood fuse block. With a approved test lamp probe both test points of the ECM/throttle fuse. The test lamp should illuminate on both test points of the fuse.

⇒	If the test lamp illuminates at both test points of the fuse, repair the ignition 1 voltage circuit between the ECM/throttle fuse and the ECM. test for an open/high resistance. If the circuit tests normal, replace the ECM. All wire circuit resistance should measure less than 2 ohms.

⇒	If the test lamp only illuminates at one test point of the ECM/throttle fuse, repair the short to ground in the ignition 1 voltage circuit between the fuse and the ECM.

⇒	If the test lamp does not illuminate on either test point of the ECM/throttle fuse, replace the underhood fuse block. Refer to Underhood Electrical Center or Junction Block Replacement .

8. With an approved test lamp, test for voltage on both test points of the following fuses

⇒	If the test lamp fails to illuminate on one test point of each fuse, replace the underhood fuse block. Refer to Underhood Electrical Center or Junction Block Replacement .

•	The ENG 1 fuse

•	The ECM/throttle fuse

•	The INJ A fuse

•	The INJ B fuse

•	The O2A fuse

•	The O2B fuse

Component Testing

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.