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 code.

DTC P1682 is a Type A code.

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

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

1. If DTCs P0685, P0689, or P0690 are set, diagnose those DTCs first.
2. 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.
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.

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

Testing the Ignition 1 Signal Circuit

Important: A resistance of 5 ohms or greater in the circuit will cause the DTC to set.

1. Ignition ON, verify that B+ is available to both test points of the fuse from the powertrain relay to the ECM.

⇒	If B+ is only available on one test point of the fuse, test the ignition 1 voltage circuit from the fuse to the ECM for a short to ground. If the circuit tests normal, replace the ECM.

⇒	If B+ is not available on either test point of the fuse, replace the underhood fuse block.

2. Ignition OFF, disconnect the ECM C1 connector.
3. Ignition ON, verify that B+ is available at C1-19.

⇒	If B+ is not available, test the ignition 1 voltage circuit for an open/high resistance condition. If the circuit tests normal, replace the ECM.

4. If all circuits test normal, replace the ECM.

Testing the EC Ignition Relay Feedback Circuit

Important: A resistance of 5 ohms or greater in the circuit will cause the DTC to set.

1. Ignition OFF, remove the powertrain relay from the underhood fuse block.
2. Ignition ON, connect a 3A fused jumper wire from B+ to the powertrain ignition 1 voltage circuit terminal. Verify that the EC Ignition Relay Feedback parameter displays B+ on the scan tool.

⇒	If the scan tool parameter is less than the specified value, test the ignition 1 voltage circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM.

Perform the Diagnostic Repair Verification