Diagnostic Aids

WARNING: This page does not describe the selected car, but rather 9 other vehicles, including the 2003 Ford RV Cutaway, 2003 Ford Pickup, 2003 Ford F550 Super Duty, 2003 Ford F450 Super Duty, and 2003 Ford Excursion. However, it is still accessible from the selected car via links, so may be relevant.

Perform this test only when directed by QUICK TEST or if no DTCs are present and tachometer is inoperative. This test is only intended to diagnose the following components and circuits.

Wiring Harness Circuits (VPWR, GND & TACH Signal)
Tachometer

Excursion & F250-550

Tachometer is controlled by instrument cluster. Instrument cluster receives engine speed information (RPM) from PCM through Standard Corporate Protocol (SCP) communications network. See Fig 1.

F650-750

Tachometer is controlled by TAC output circuit on PCM. See Fig 2.

Fig 1: Identifying Tachometer Circuits (Excursion & F250-550)

Courtesy of FORD MOTOR CO.

Fig 2: Identifying Tachometer Circuits (F650-750)

Courtesy of FORD MOTOR CO.