For 1990-2009 cars

The PCM monitors ignition voltage on circuit 439 at all times with reference to circuit 551 (ground) when the engine is running. Ignition voltage from circuit 439 can be read on the scan tool as IGNITION 1 voltage. DTC P0561 sets when the PCM detects an instantaneous change in ignition voltage.

### DTC Parameters

DTC P0561 will set if the ignition voltage changes more than 3 volts when:

• | The condition exists for longer than 0.5 seconds.

• | The condition exists twice in one ignition cycle.

• | The engine is running.

DTC P0561 diagnostic runs continuously with the engine running.

DTC P0561 is a type D DTC.

### Diagnostic Aids

Important: If DTC P1635 is also set, diagnose that DTC first.

Important: DTC P1635 will NOT set if a short-to-B+ occurs on vehicles built prior to VIN 1Z200000.

A short to B+ on one of the 5-volt reference circuits (EGR position sensor, fuel tank pressure sensor, MAP sensor, or TP sensor) may set DTC P0561. DTC P0562 and P0711 may also set as a result of a short to B+ on the five volt reference circuit.

To locate this intermittent problem, use the scan tool to monitor IGNITION 1 voltage while wiggling the wires. Wiggling the wires while monitoring IGNITION 1 voltage may locate the area where an open in the wiring exists.

Check fuses, battery terminals, the generator charging post terminal, and the ignition switch harness connector for tightness.