GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2007 🢒 STS 🢒 DTC 🢒 DTC P0685, P0686, P0687, P0689, or P0690

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 P0686: Engine Controls Ignition Relay Control Circuit Low Voltage

DTC P0687: Engine Controls Ignition Relay Control Circuit High Voltage

DTC P0689: Engine Controls Ignition Relay Feedback Circuit Low Voltage

DTC P0690: Engine Controls Ignition Relay Feedback Circuit High Voltage

Diagnostic Fault Information

Important: A condition with the main relay will set multiple DTCs. The DTCs listed in the table will only set if a condition exists with the main relay.

Circuit

Short to Ground

High Resistance

Open

Short to Voltage

Signal Performance

B+ Supply Voltage - Coil

P0685

P0685

P0685

--

--

B+ Supply Voltage - Switch

--

P0689

P0689

P0690

--

Relay Control Circuit

P0686

P0685

P0685

P0687

P0685

Ignition 1 Voltage Circuit

--

P0689

P0689

P0690

--

Circuit/System Description

The engine controls (EC) ignition relay, or main 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 switch 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. When the ECM commands the main relay ON, ignition 1 voltage is supplied to the following fuses in the underhood fuse block:

    • The ECM or HFV6 ECM Fuse
    • The TOS Fuse - CTS only
    • The PRE O2/CAM Fuse
    • The POST O2 Fuse
    • EVEN INJ/COIL Fuse
    • ODD INJ/COIL Fuse

The ignition 1 voltage that is supplied to the ECM through the ECM fuse, provides power to the internal ECM circuits associated with the throttle actuator control (TAC) operation.

Conditions for Running the DTC

P0685 and P0686

    • The battery voltage is between 10.5-18 volts.
    • The ignition is OFF.
    • The main relay has been commanded OFF.
    • The DTCs run continuously once the above condition is met.

P0687, P0689, and P0690

    • The battery voltage is between 10.5-18 volts.
    • The ignition is ON.
    • The main relay has been commanded ON.
    • The DTCs runs continuously once the above condition is met.

Conditions for Setting the DTC
    • The commanded state of the output driver module (ODM) and the actual state of the control circuit do not match.
        OR
    • The ECM detects that main relay feedback voltage is not within a predicted range, when the main relay is commanded ON or OFF.
    • Either condition is present for more than 2 seconds.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC
    • The control module turns OFF the malfunction indicator lamp (MIL) after 4 consecutive ignition cycles that the diagnostic runs and does not fail.
    • 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 emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

Diagnostic Aids
    • This test procedure requires 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 tightness.
    • The lower connector of the ECM is connector C1 and the upper connector of the ECM is connector C2. Refer to Engine Controls Component Views .
    • Use the J 35616-A/BT-8637 Connector Test Adapter Kit for any test that requires probing the underhood fuse block terminals, component wire harness terminals, or the ECM wire harness connector terminals.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    •  Engine Control Module Connector End Views
    •  Engine Controls Connector End Views

Scan Tool Reference

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

Special Tools Required

J 43244 Relay Puller Pliers

Circuit/System Verification
  1. Ignition ON, clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Ignition ON, observe the DTC information with a scan tool.
  4. View the DTC information with a scan tool. DTCs P0685, P0686, P0687, P0689, or P0690 should not set.

Circuit/System Testing
  1. Ignition OFF, disconnect the EC ignition or main relay.

    2. Important: The test lamp is used to load the circuit and may not illuminate.

  2. Connect a test lamp between the B+ supply circuit to the coil side of the main relay and the negative terminal of the battery.
  3. Ignition ON, test for less than 0.1 volt between the B+ voltage circuit of the main relay and the positive battery terminal.
    4. ⇒If greater than 0.1 volt, repair the B+ voltage circuit to the coil side of the main relay for a short to ground or an open/high resistance.

    Important: The test lamp is used to load the circuit and may not illuminate.

  4. Connect a test lamp between the B+ voltage supply circuit to the switch side of the main relay and the negative terminal of the battery.
  5. Ignition ON, test for less than 0.1 volt between the B+ voltage circuit of the main relay and the positive battery terminal.
    6. ⇒If greater than 0.1 volt, repair the B+ voltage circuit to the switch side of the main relay for a short to ground or an open/high resistance.
  6. With the ignition OFF, connect a test lamp between the control circuit of the main relay and the B+ voltage supply circuit to the coil side of the main relay.
  7. Turn ON the ignition. The test lamp should turn ON when the ignition switch is cycled ON and OFF when the ignition switch is cycled OFF.
    8. ⇒If the test lamp remains ON all the time, test for a short to ground on the control circuit. If the circuit/connections test normal, replace the ECM.
    ⇒If the test lamp remains OFF all the time, test for a short to voltage or an open/high resistance on the control circuit. If circuit/connections test normal, replace the ECM.

    Important: The ignition 1 voltage circuit is between the main relay and the ECM. The ignition 1 voltage is a feedback circuit.

  8. Connect a 15-amp fused jumper wire between the B+ supply voltage circuit and the ignition 1 voltage circuit of the main relay.
  9. Attempt to start the engine. The engine should start.
    10. ⇒If the engine does not start, test the ignition 1 voltage circuit between the main relay and the ECM for a short to ground or for an open/high resistance. If the circuit/connections test normal, replace the ECM.
  10. If all circuits/connections test normal, test or replace the main relay.

Component Testing
  1. Measure for 70-110 ohms of resistance between terminals 85 and 86 of the main relay.
    2. ⇒If the resistance is not within the specified range, replace the main relay.
  2. Measure for infinite resistance between the following terminals of the main relay:
    3. • 30 and 86
    • 30 and 87
    • 30 and 85
    • 85 and 87
    ⇒If continuity is detected, replace the main relay.
  3. Connect a 20-amp fused jumper wire from the positive terminal of the battery to relay terminal 85. Connect a jumper wire from the negative terminal of the battery to relay terminal 86. Measure for less than 2 ohms between terminals 30 and 87 of the relay.
    4. ⇒If the resistance measures more than 2 ohms, replace the main relay.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Relay Replacement
    •  Control Module References for engine control module replacement, setup, and programming