There are 2 ignition 1 voltage circuits supplied to the engine control module (ECM). The first ignition circuit is provided by the powertrain relay, through a fuse. This ignition 1 voltage circuit supplies power to all the internal ECM circuits associated with the throttle actuator control (TAC) operation. The second ignition 1 voltage circuit is supplied by the run/crank relay through a fuse, and is used to power the remaining internal ECM circuits. If the ECM detects a voltage difference between the 2 ignition 1 voltage circuits, DTC P1682 will set.

The ECM detects that the voltage level difference is greater than 3 volts between the 2 ignition 1 voltage circuits for less than 1 second.

DTC P1682 is a Type A DTC.

DTC P1682 is a Type A DTC.

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

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References

Special Tools

J 35616 GM-Approved Terminal Test kit

1. Ignition OFF, open the hood to disable the Auto-Stop function. Refer to Hybrid Modes of Operation Description.
2. Ignition ON, verify the scan tool hood position parameter displays Open.

⇒	If the hood position does not display Open, refer to Diagnostic Trouble Code (DTC) List - Vehicle for DTC P254F.

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

3. If DTCs P0685 or P0690 are set, diagnose those DTCs first.
4. Ignition ON, engine OFF, observe both the Ignition 1 Voltage signal and the EC Ignition Relay Feedback signal parameters on the scan tool. Both parameter values should display no more than 3 volts difference between the 2 parameters.
5. 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.

Important: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.

1. Ignition OFF, open the hood to disable the Auto-Stop function. Refer to Hybrid Modes of Operation Description.
2. Ignition ON, verify the scan tool hood position parameter displays Open.

⇒	If the hood position does not display Open, refer to Diagnostic Trouble Code (DTC) List - Vehicle for DTC P254F.

3. Ignition OFF, disconnect the powertrain relay.
4. Ignition ON, verify that a test lamp does not illuminate between the powertrain relay controlled output circuit terminal and ground.

⇒	If the test lamp illuminates, test the powertrain relay controlled output circuit for a short to voltage.

5. Ignition OFF, verify that a test lamp illuminates between the powertrain relay coil voltage supply circuit terminal and ground.

⇒	If the test lamp does not illuminate, test the powertrain relay coil voltage supply circuit for a short to ground or an open/high resistance.

6. Verify that a test lamp illuminates between the powertrain relay switch voltage supply circuit terminal and ground.

⇒	If the test lamp does not illuminate, test the powertrain relay switch voltage supply circuit for an open/high resistance.

7. Disconnect the ECM.
8. Ignition ON, verify that a test lamp illuminates between ECM connector terminal X1-19 and ground.

⇒	If the test lamp does not illuminate, test the ignition 1 relay controlled output circuit for a short to ground or open/high resistance.

⇒	If the circuit tests normal and its fuse is open, replace the ECM.

9. Ignition OFF, connect the harness connector at the ECM.
10. Ignition ON, connect a jumper wire between the powertrain relay voltage supply circuit terminal and the powertrain relay controlled output circuit terminal. Verify the EC Ignition Relay Feedback parameter indicates battery positive voltage.

⇒	If not the specified value, test the powertrain relay controlled output circuit for a short to ground or an open/high resistance. If the circuit tests normal and its fuse is open, replace the ECM.

11. If all circuits test normal, replace the powertrain relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.