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Powertrain Relay Diagnosis




Powertrain Relay Diagnosis

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.

Typical Scan Tool Data





Circuit/System Description

The powertrain 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 powertrain relay. 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 the ECM, and to several additional circuits.

Diagnostic Aids

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

Reference Information
Schematic Reference

Engine Controls Schematics (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information
Special Tools

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

Circuit/System Verification

1. Engine running, command the powertrain relay ON and OFF, with a scan tool, while observing the following powertrain relay coil control circuit status parameters.

* Powertrain relay coil control Ckt. Short Gnd Test Status
* Powertrain relay coil control Ckt. Open Test Status
* Powertrain relay coil control Ckt. Short Volts Test Status
Each parameter should toggle between OK and Not Run or Not Run and OK

2. Ignition ON, engine OFF, with a test lamp, probe both test points of all the fuses that are powered by the powertrain relay. The test lamp should illuminate ON for at least one test point of each fuse.
3. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

Important: You must perform the Circuit/System Verification first.


1. Ignition OFF, disconnect the powertrain relay.
2. Ignition ON, verify that a test lamp illuminates between the powertrain relay coil B+, and ground.

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the battery positive cable to the underhood fuse block.

3. Ignition OFF, verify that a test lamp does not illuminate between the powertrain relay coil B+ circuit and the control circuit.

• If the test lamp illuminates, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM.

4. Remove the test lamp.
5. Command the powertrain relay ON, with a scan tool. Verify with a scan tool that the powertrain relay Ckt. Short Volts Test Status parameter is OK.

• If not the specified value, test the control circuit for a short to voltage. If the circuit tests normal, replace the ECM.

6. Test the coil side of the powertrain relay for 65-110 ohms.

• If not within the specified value, replace the relay.

7. Ignition OFF, disconnect the ECM C1 connector.
8. Test the powertrain relay control circuit for an open/high resistance.

• If the circuit tests normal, replace the ECM.

9. Verify that a test lamp does not illuminate between the relay ignition 1 voltage circuit and ground.

• 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.

10. Verify that a test lamp illuminates between the relay switch B+ and ground.

• 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.

11. Connect a 20 A fused jumper wire between the relay switch B+ and the relay ignition 1 voltage circuit.
12. Ignition ON, engine OFF, monitor the EC Ignition Relay Feedback parameter with a scan tool. The parameter should display B+.

• 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.

13. If all circuits test normal, replace the relay.

Repair Instructions

* Engine Control Module Programming and Setup (Programming and Relearning)
* Engine Control Module Replacement (Service and Repair)
* Relay Replacement (Attached to Wire Harness) (Relay Replacement (Attached to Wire Harness))Relay Replacement (Within an Electrical Center) (Relay Replacement (Within an Electrical Center))

Repair Verification

1. Install any components that have been removed or replaced during diagnosis.
2. Perform any adjustment, programming, or setup procedures that are required when a component or module is removed or replaced.
3. Clear the DTCs.
4. Turn OFF the ignition for 60 seconds.
5. Ignition ON, command the powertrain relay ON and OFF with a scan tool, while observing the powertrain relay circuit status parameters, The circuit status parameters should change from OK to Not Run or Not Run to OK.

• If another DTC is present, refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code Descriptions) and perform the appropriate diagnostic procedure.

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