Power Take-Off Switch and Circuit

WARNING: This page does not describe the selected car, but rather 30 other vehicles, including the 2004 Mercury Sable, 2004 Mercury Mountaineer, 2004 Mercury Monterey, 2004 Mercury Marauder, and 2004 Mercury Grand Marquis. However, it is still accessible from the selected car via links, so may be relevant.

The Power Take-Off (PTO) circuit (Fig 1) is used by the PCM to disable some of the OBD II Monitors during PTO operation. The PTO switch is normally open. When the PTO unit is activated the PTO switch is closed and battery voltage is supplied to the PTO input circuit. This indicates to the PCM that an additional load is being applied to the engine.

When the PTO unit is activated, the PCM disables some OBD-II monitors, which may not function reliably during PTO operation. Without the PTO circuit information to the PCM, false Diagnostic Trouble Codes (DTCs) may be set during PTO operation. Prior to an Inspection/Maintenance test, the vehicle will have to be operated with the PTO disengaged long enough to successfully complete the OBD-II Monitors.

Fig 1: Identifying Power Take-Off (PTO) Switch And Circuit To PCM

Courtesy of FORD MOTOR CO.