For 1990-2009 cars

### 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 P0686 00: Engine Controls Ignition Relay Control Circuit Low Voltage
DTC P0687 00: Engine Controls Ignition Relay Control Circuit High Voltage
DTC P0688 00: Engine Controls Ignition Relay Feedback Circuit
DTC P0689 00: Engine Controls Ignition Relay Feedback Circuit Low Voltage

### Diagnostic Fault Information

Circuit | Short to Ground | High Resistance | Open | Short to Voltage | Signal Performance
--- | --- | --- | --- | --- | ---
Battery Supply Voltage - Coil | P0686 00 | P0686 00 | P0686 00 | -- | --
Battery Supply Voltage - Armature | P0689 00 | P0689 00 | P0689 00 | -- | --
Relay Control Circuit | -- | P0686 00 | P0686 00 | P0687 00 | --
Relay Feedback Circuit | P0689 00, P0688 00 | P0689 00, P0688 00 | P0689 00, P0688 00 | -- | --

### Circuit/System Description

The powertrain relay is an electrical switch that opens and closes under the control of the engine control module. The powertrain 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. The output driver module for the ignition main relay also incorporates a fault detection circuit, which is continuously monitored by the ECM. When the ECM commands the powertrain relay ON, switched battery voltage is supplied to fuses in the underhood fuse block. The switched battery 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 switched battery circuit to confirm that the powertrain relay contacts have closed.

### Conditions for Running the DTC

#### P0686 00 and P0687 00

• | The ignition is ON, or the engine is running.

• | DTC P0606 00 is not set.

#### P0688 00 and P0689 00

• | The ignition is ON.

• | DTC P0686 00 or P0687 00 is not set.

### Conditions for Setting the DTC

#### P0686 00 and P0687 00

• | Shortcut to ground in the control circuit

| OR

• | Shortcut to voltage in the control circuit

### Action Taken When the DTC Sets

#### P0686 00, P0687 00, P0688 00 and P0689 00

DTCs P0686 00, P0687 00, P0688 00 are Type C DTCs.

### Conditions for Clearing the DTC

#### P0686 00, P0687 00, P0688 00 and P0689 00

• | DTCs P0686 00, P0687 00, P0688 00 are Type C DTCs.

• | With a DTC set, the engine may crank for an extended period of time at start-up.

### Diagnostic Aids

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

• | An open in the relay control circuit will cause no communication with the ECM when the ignition switch is cycled OFF and then ON after the initial failure. The malfunction indicator lamp (MIL) will flash rapidly and other relays can be heard turning on and off with the ignition ON.

• | 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.

• | Use the EL-35616-E GM-Approved Terminal Test 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

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 diagnostic tester information

#### Special Tools

EL-35616-E GM-Approved Terminal Test Kit

For equivalent regional tools, refer to Special Tools.

### Circuit/System Verification

1. Ignition ON, you should be able to communicate with the ECM using a scan tool.
2. Ignition ON, view the DTC information with a scan tool. DTC P0686 00, P0687 00, P0688 00, or P0689 00 should not set.
3. Operate the vehicle within the conditions for running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the freeze frame/failure records data.

### Circuit/System Testing

1. Ignition OFF, remove the KR75 Powertrain Relay, from the underhood fuse block.
2. Test for greater than 11 V between KR75 Powertrain Relay socket terminals 30, 85 and ground.

⇒ | If the voltage measures less than 11 V, repair the open or high resistance between B+ and KR75 Powertrain Relay socket terminal 30, 85.

3. Test for less than 0.3 V between KR75 Powertrain Relay socket terminal 86 and ground.

⇒ | If the voltage measures greater than 0.3 V, test the control circuit for a short to voltage between KR75 Powertrain Relay socket terminal 86 and K20 Engine Control Module (ECM) terminal 21 (X1). If the circuit tests normal, replace the K20 Engine Control Module (ECM).

4. Verify that a test lamp does not illuminate between KR75 Powertrain Relay socket Terminal 85 and KR75 Powertrain Relay socket terminal 86.

⇒ | If the test lamp illuminates, test the control circuit for a short to ground between KR75 Powertrain Relay socket terminal 86 and K20 Engine Control Module (ECM) terminal 21 (X1). If the circuit tests normal, replace the K20 Engine Control Module (ECM).

5. Turn the ignition ON. The test lamp should illuminate.

⇒ | If the test lamp is OFF, test the control circuit for an open/high resistance between KR75 Powertrain Relay socket terminal 86 and K20 Engine Control Module (ECM) terminal 21 (X1). If the circuit tests normal, replace the K20 Engine Control Module (ECM).

6. Test for less than 0.3 V between KR75 Powertrain Relay socket terminal 87 and ground.

⇒ | If the voltage measures greater than 0.3 V, test the ignition voltage circuit for a short to voltage between KR75 Powertrain Relay socket terminal 87 and K20 Engine Control Module (ECM) terminal 50 (X1), 6 (X2). If the circuit tests normal, replace the K20 Engine Control Module (ECM).

7. Ignition OFF, disconnect K20 Engine Control Module (ECM), test for less than 5 Ω between KR75 Powertrain Relay socket terminal 87 and K20 Engine Control Module (ECM) terminal 50 (X1), 6 (X2).

⇒ | If the resistance measures greater than 5 Ω, repair the open or high resistance between K20 Engine Control Module (ECM) terminal 50 (X1), 6 (X2) and KR75 Powertrain Relay socket terminal 87.

8. Ignition OFF, connect K20 Engine Control Module (ECM) connector (X1), insert KR75 Powertrain Relay. Turn the ignition ON. Test for greater than 11 V between K20 Engine Control Module (ECM) terminal 6 (X2) and ground.

⇒ | If the voltage measures less than 11 V, replace the KR75 Powertrain Relay.

### Component Testing

#### Static Test

1. Measure for 70-110 Ω between terminals 85 and 86 of the KR75 Powertrain Relay.

⇒ | If the resistance is not within the specified range, replace the KR75 Powertrain Relay.

2. Measure for infinite resistance between following terminals of the KR75 Powertrain Relay:

• | Terminals 30 and 86

• | Terminals 30 and 87

• | Terminals 30 and 85

• | Terminals 85 and 87

⇒ | If continuity is detected, replace the KR75 Powertrain Relay.

3. Connect a 20 A fused jumper wire from the positive terminal of the battery to KR75 Powertrain Relay socket terminal 85. Connect a jumper wire from the negative terminal of the battery to KR75 Powertrain Relay socket terminal 86. Measure for less than 5 Ω between KR75 Powertrain Relay socket terminal 30 and KR75 Powertrain Relay socket terminal 87.

⇒ | If the resistance measures more than 5 Ω, replace the KR75 Powertrain 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