For 1990-2009 cars

### Circuit Description

The engine control module (ECM) monitors vehicle system voltage by monitoring the voltage on circuit 2740 coming from the main relay, which is referenced to the ECM case ground. Each of the 3 main relay pins going into the ECM are tied together internally in the ECM. When the ignition voltage is present at the ignition 1 input to the ECM, circuit 339, the ECM will command the main relay ON by supplying ground to the main relay coil circuit. When the relay is energized, battery voltage should be present on each circuit 2740 at the ECM. DTC P0560 will set if the ECM detects very low voltage on circuit 2740 for a certain length of time after the engine has been running when the main relay has been commanded ON.

### Conditions for Setting the DTC

DTC P0560 will set if main relay voltage on circuit 2740 is less than 2.5 volts when:

• | The condition exists for longer than 0.2 seconds.

• | The main relay is commanded ON because the ECM detected ignition voltage present at the ignition 1 input to the ECM.

• | The engine run time is greater than 3 minutes.

• | Vehicle speed is present.

DTC P0560 diagnostic runs continuously once the above conditions have been met.

DTC P0560 is a type D DTC.

### Diagnostic Aids

DTC P0560 indicates that when the main relay was commanded ON, main relay voltage was lost on circuit 2740 for longer than the time listed under DTC parameters.

The DTC does NOT indicate a fault in the battery or ignition 1 input to the ECM.

Turn the ignition ON and OFF while listening for the main relay click in the underhood fuse block. Replace the relay if it intermittently sticks.

If main relay voltage is not present at the ECM as soon as the ignition is turned ON, the scan tool will not communicate with the ECM. If main relay voltage is lost during the ignition cycle, the ECM will continue to communicate with the scan tool for the rest of the ignition cycle.

If the main relay is inoperative, refer to DTC U2105 in the body electrical diagnostics service manual, which will diagnose the main relay and its control circuit.