GM Service Manual Online
For 1990-2009 cars only

Diagnostic Instructions

    •  Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    •  Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each of the diagnostic category.

DTC Descriptors

DTC P0685: Engine Controls Ignition Relay Control Circuit

DTC P0690: Engine Controls Ignition Relay Feedback Circuit High Voltage

Diagnostic Fault Information

Circuit

Short to Ground

High Resistance

Open

Short to Voltage

Signal Performance

Battery Supply Voltage - Coil

P0685

P0685

P0685

--

--

Relay Control Circuit

P0685

P0685

P0685

P0685

--

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

Battery Supply Voltage - Coil

--

0 V

0 V

--

Battery Supply Voltage - Armature

--

0 V

0 V

--

EC Ignition Relay Control

--

0 V

0 V

--

EC Ignition Relay Feedback

11.9-12.9 V

0 V

0 V

More than 2 V¹

¹ DTC P0690 will set if the ECM detects voltage when the ignition is in the OFF position.

Circuit/System Description

The powertrain relay is a normally open relay. The relay switch is held in the open position by spring tension. Battery positive voltage is supplied directly to the relay coil and the relay switch contact at all times. The engine control module (ECM) supplies the ground path to the relay coil control circuit through an output driver module (ODM). The ODM for the powertrain relay also incorporates a fault detection circuit, which is continuously monitored by the ECM. When the ECM commands the powertrain relay ON, ignition 1 voltage is supplied to fuses in the underhood fuse block.

The ignition 1 voltage that is supplied to the ECM, 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 powertrain relay contacts have closed.

Conditions for Running the DTC

P0685

    • The battery voltage is between 9-18 volts.
    • The ignition is ON.
    • The powertrain relay has been commanded ON.

P0690

    • The battery voltage is between 9-16 volts.
    • The ignition is OFF.
    • The powertrain relay has been commanded OFF.

Conditions for Setting the DTC

P0685

    • The commanded state of the ODM does not match and the actual state of the control circuit.
    • The condition is present for more than 5 seconds.

P0690

    • The ECM detects more than 2 volts on the ignition 1 voltage circuit to the ECM.
    • The condition is present for more than 2 seconds.

Action Taken When the DTC Sets

    • DTCs P0685 and P0690 are Type B DTCs.
    • DTC P0689 is a Type C DTC.

Conditions for Clearing the DTC

    • DTCs P0685 and P0690 are Type B DTCs.
    • DTC P0689 is a Type C DTC.

Diagnostic Aids

    • This test procedure assumes that the vehicle battery has passed a load test and is completely charged. Refer to Battery Inspection/Test.
    • When disconnecting electrical connectors or removing fuses and relays from a fuse block, always inspect the component electrical terminals for corrosion and the mating electrical terminals for correct tension.

Reference Information

Schematic Reference

    •  Engine Controls Schematics
    •  Power Distribution Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Special Tools

J 43244 Relay Puller Pliers

Circuit/System Verification

  1. Ignition ON, verify that the Feedback Circuit parameter indicates B+ voltage.
  2. Ignition ON, command the powertrain relay ON and OFF. Listen or feel to verify that the powertrain relay turns ON and OFF with the commanded states.

Circuit/System Testing

  1. With the ignition OFF, remove the powertrain relay from the underhood fuse block.
  2. With the ignition ON, measure for battery positive voltage, B+, between the relay coil voltage supply circuit terminal 85 and ground.
  3. If the voltage measures less than B+, repair the open or high resistance in the circuit to the relay coil. All wire circuit resistance should measure less than 2 ohms.
  4. Measure for voltage between the relay coil control circuit terminal 86 and ground.
  5. If voltage is measured on the control circuit of the relay, test for a short to voltage.
  6. Connect a test lamp between the battery positive voltage supply circuit of the relay coil terminal 85 and the relay coil control circuit terminal 86. Use a scan tool to command the powertrain relay ON and OFF. The test lamp should turn ON and OFF when toggling between the commanded states.
  7. If the test lamp stays ON all the time, test for a short to ground on the relay coil control circuit or a faulty ECM.
    If the test lamp stays OFF all the time, test for an open or high resistance on the relay coil control circuit or a faulty ECM. All wire circuit resistance should measure less than 2 ohms.
  8. Measure for B+ between the relay armature supply circuit terminal 30 and ground.
  9. If the voltage measures less than B+, repair the open or high resistance in the circuit to the relay armature. All wire circuit resistance should measure less than 2 ohms.
  10. With the ignition ON, test for voltage on each test point of the ETC fuse.
  11. If voltage is present, test the ignition 1 voltage circuit between the ECM, the powertrain relay, and the ETC fuse for a short to voltage.
    If both circuits test normal, replace the ECM.
  12. Connect a 20A fused jumper wire between the B+ terminal 30 and the ignition 1 voltage terminal 87 of the powertrain relay at the underhood fuse block. With a test lamp, probe both test points of the ETC fuse.
  13. If the test lamp illuminates at both test points of the ETC fuse, repair the ignition 1 voltage circuit between the powertrain relay and the ECM for an open, high resistance, or a faulty ECM. All wire circuit resistance should measure less than 2 ohms.
    If the test lamp only illuminates at one test point of the ETC fuse, repair the short to ground in the ignition 1 voltage circuit between the fuse and the applicable component. Replace the fuse, as necessary.
    If the test lamp does not illuminate on either test point of the ETC fuse, repair the open or high resistance between the powertrain relay and the ETC fuse. All wire circuit resistance should measure 2 ohms or less.
  14. With a test lamp, test for voltage on both test points of the following fuses:
  15. • ETC Fuse
    • Emission 1 Fuse
         ⇒If the test lamp fails to illuminate on one test point of each fuse, repair the open or high resistance between the fuse and the powertrain relay. All wire circuit resistance should measure 2 ohms or less.

Component Testing

    • Measure for 70-110 ohms between terminals 85 and 86 of the relay.
       ⇒If the resistance is not within the specified range, replace the relay.
    • Measure for infinite resistance between terminals 30 and 86 of the relay.
       ⇒If continuity is detected, replace the relay.
    • Measure for infinite resistance between terminals 30 and 87 of the relay.
       ⇒If continuity is detected, replace the relay.
    • Measure for infinite resistance between terminals 30 and 85 of the relay.
       ⇒If continuity is detected, replace the relay.
    • Measure for infinite resistance between terminals 85 and 87 of the relay.
       ⇒If continuity is detected, replace the relay.
    • Connect a 20A fused jumper wire from the battery positive cable at the battery, to relay terminal 85. Connect a jumper wire from the negative battery cable at the battery, to relay terminal 86. Measure for less than 2 ohms between terminals 30 and 87 of the relay, with a DMM.
       ⇒If the resistance measures more than 2 ohms, replace the relay.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Relay Replacement
    •  Control Module References for ECM replacement, setup, and programming