There are 2 ignition 1 voltage circuits supplied to the engine control module (ECM). The first ignition 1 voltage circuit is provided by the powertrain relay, which is main relay 6, 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 run/crank relay provides the second ignition 1 voltage circuit to the ECM, through a fuse. This ignition 1 voltage provides power to other internal ECM circuits, except those associated with TAC operation. The ECM continuously monitors the voltage level difference between the two circuits.

The ignition 1 voltage of the Run/Crank relay is more than 2 volts different than the ignition 1 voltage of the powertrain relay for more than 2 seconds.

DTC P1682 is a Type A DTC.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Engine Control Module Description

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

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.

⇒	If the vehicle passes the Circuit/System Verification test, operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records data list.

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 run/crank 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 X1 connector.
3. Ignition On, verify that B+ is available at X1-19.

⇒	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, which is main relay 6, from the underhood fuse block.
2. Ignition ON, connect a 3A fused jumper wire from B+ to the powertrain ignition 1 voltage circuit terminal 87. 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 after completing the diagnostic procedure.