P0503 - Vehicle Speed Sensor (VSS) A Intermittent/Erratic/High

WARNING: This page does not describe the selected car, but rather 32 other vehicles, including the 2008 Mercury Sable, 2008 Mercury Mountaineer, 2008 Mercury Milan, 2008 Mercury Mariner, and 2008 Mercury Grand Marquis. However, it is still accessible from the selected car via links, so may be relevant.

P0503 - VEHICLE SPEED SENSOR (VSS) A INTERMITTENT/ERRATIC/HIGH

Description:	Indicates poor or noisy VSS performance. Vehicle speed data is received from either the VSS, the transfer case speed sensor (TCSS), or the anti-lock brake system (ABS) control module.
Possible Causes:	Noisy VSS/TCSS input signal from the radio frequency interference / electromagnetic interference (RFI/EMI) external sources, such as ignition components or the charging circuit Damaged VSS or driven gears Damaged TCSS Damaged wiring harness or connectors Malfunction in the module(s) or circuit connected to the VSS/TCSS circuit Aftermarket add-on
Diagnostic Aids:	Monitor the VSS PID while driving the vehicle, and check for intermittent vehicle speed indication. Verify the ignition and charging systems are functioning correctly.
Application		Key On Engine Off	Key On Engine Running	Continuous Memory
F-Super Duty		refer to PINPOINT TEST DF .
Expedition, Navigator, Sable, Taurus, Taurus X		The powertrain control module (PCM) uses information from the anti-lock brake system (ABS) module and the transmission control module (TCM) to calculate vehicle speed. Check these modules for DTCs.
All others		refer to PINPOINT TEST DP .