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 diagnostic category.

DTC Descriptors

DTC P0685: Engine Controls Ignition Relay Control Circuit

DTC P0689: Engine Controls Relay Feedback Circuit Low Voltage

DTC P0690: Engine Controls Relay Feedback Circuit High Voltage

Diagnostic Fault Table

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Relay Coil B+

P0685

P0685

--

--

Relay Switch B+

P0689

P0689

--

--

Relay Coil Control

P0685

P0685

P0685

--

Relay Ignition Output Ignition 1 Voltage

P0689

P0689

P0690

--

Typical Scan Tool Data

EC Ignition Relay

Display Parameters

Normal Range

Short to Ground

Open/High Resistance

Short to Voltage

Operating Conditions: Ignition ON, engine OFF, main relay command ON

EC Ignition Main Relay Circuit Status

OK/Incomplete

Short to GRD/Open

Short to GRD/Open

Short to B+

EC Ignition Main Relay Command

ON

ON

ON

ON

EC Ignition Main Relay Feedback Signal

12-12.9 V

0.0 V

0.0 V

12-12.9 V

Circuit/System 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). The ODM output control is configured to operate as a low side driver for the main relay. The ODM for the main relay also incorporates a fault detection circuit, which is continuously monitored by the ECM. When the ECM commands the main relay ON, ignition 1 voltage is supplied to several circuits.

Conditions for Running the DTC

P0685

    • The ignition is ON.
    • The battery voltage is between 9-16 volts.

P0689

    • The ignition is ON.
    • The main relay is commanded ON.
    • DTC P0685 is not set.

P0690

    • This DTC will run with the ignition ON or OFF.
    • This DTC will run when the main relay is commanded ON or OFF.
    • DTC  P0685 is not set.

Conditions for Setting the DTC

P0685

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

P0689

    • The ECM detects less than 5 volts on the ignition 1 voltage circuit to the ECM.
    • The condition is present for more than 5 seconds.

P0690

    • The ECM detects more than 16 volts on the ignition 1 voltage circuit to the ECM when the relay is commanded ON.
    • The ECM detects more than 2 volts on the ignition 1 voltage circuit to the ECM when the relay is commanded OFF.
    • The condition is present for more than 2 seconds.

Action Taken When the DTC Sets

DTCs P0685, P0689, and P0690 are Type B codes.

Conditions for Clearing the DTC

DTCs P0685, P0689, and P0690 are Type B codes.

Diagnostic Aids

This test procedure requires that the vehicle battery has passed a load test and is completely charged. Refer to Battery Inspection/Test .

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    •  Engine Controls Connector End Views
    •  Engine Control Module Connector End Views
    •  Electrical Center Identification Views

Electrical Information Reference

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

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

    •  Scan Tool Data List
    •  Scan Tool Data Definitions
    •  Scan Tool Output Controls

Special Tools Required

    • J 35616 GM-Approved Terminal Test Kit
    • J 43244 Relay Puller Pliers

Circuit/System Verification

    Important: On the scan tool, the main relay is referred to as the EC ignition relay.

  1. Ignition ON, engine OFF, command the main 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, with a test lamp, probe both test points of all of the fuses that are powered by the main relay. The test lamp should illuminate on at least one test point of each fuse.
  3. 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.

Circuit/System Testing

  1. Ignition OFF, disconnect the main relay.
  2. Ignition ON, verify that a test lamp does not illuminate between the relay coil control circuit terminal R50 and ground.
  3. If the test lamp illuminates, test the relay coil control circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  4. Verify that a test lamp does not illuminate between the relay ignition 1 voltage circuit terminal R49 and ground.
  5. If the test lamp illuminates, test the relay ignition 1 voltage circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  6. Verify that a test lamp illuminates between the relay coil B+ terminal R47 and ground.
  7. If the test lamp does not illuminate, test the relay coil B+ circuit for a short to ground or an open/high resistance.
  8. Verify that a test lamp illuminates between the relay switch B+ terminal R48 and ground.
  9. If the test lamp does not illuminate, test the relay switch B+ circuit for a short to ground or an open/high resistance. If the circuits test normal and the fuse for the ignition 1 voltage circuit is open, test the ignition 1 voltage circuit to the ECM for a short to ground. If the circuit tests normal, replace the ECM.
  10. Connect a test lamp between the relay coil B+ terminal R47 and the relay coil control circuit terminal R50
  11. Ignition ON, command the main relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
  12. If the test lamp is always ON, test the relay coil control circuit for a short to ground. If the circuit tests normal, replace the ECM.
    If the test lamp is always OFF, test the relay coil control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.
  13. Connect a 20A fused jumper wire between the relay switch B+ terminal R48 and the relay ignition 1 voltage circuit terminal R49.
  14. Ignition ON, engine OFF, monitor the EC Ignition Relay Feedback parameter with a scan tool. The parameter should display B+.
  15. If the parameter does not display B+, test the ignition 1 voltage circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
  16. If all circuits test normal, test or replace the relay.

Component Testing

  1. Ignition OFF, disconnect the main relay.
  2. Test for 65-110 ohms of resistance between terminals 85 and 86 of the relay.
  3. If the resistance is not within the specified range, replace the relay.
  4. Test for infinite resistance between the following terminals:
  5. • Terminal 30 and 86
    • Terminal 30 and 87
    • Terminal 30 and 85
    • Terminal 85 and 87
    If not the specified value, replace the relay.
  6. Install a 20A fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 1 ohm of resistance between terminals 30 and 87.
  7. If greater than the specified range, replace the relay.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Relay Replacement
    •  Underhood Electrical Center or Junction Block Replacement
    •  Control Module References for ECM replacement, setup, and programming