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 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 ignition main 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 2 circuits.

The ignition 1 voltage of the ignition main 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.

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

Schematic Reference

Connector End View Reference

Description and Operation

Engine Control Module Description

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

1. If DTCs P0685, P0689, P0690, or B1380 are set, diagnose those DTCs first.
2. Ignition ON, engine OFF, observe 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. Ignition OFF, observe the ignition 1 voltage signal parameter on the scan tool. The parameter value should be 0 volts before the ECM powers down.

1. Ignition ON, observe the Ignition 1 Signal and EC Ignition Relay Feedback scan tool parameters to determine which is less than B+.
2. Ignition OFF, remove the relay that corresponds to the scan tool parameter that is less than B+.

Important: 6 ohms or greater in the circuit/underhood fuse block will cause the DTC to set.

3. Ignition ON, connect a 3A fused jumper wire between B+ and the applicable ignition 1 circuit terminal. Verify that the applicable scan tool parameter displays B+.

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

4. If all circuits test normal, test or replace the applicable relay/underhood fuse block.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.