P0503 Vehicle Speed Sensor "A" Intermittent/Erratic/High Trouble Code

P0503 Vehicle Speed Sensor A Intermittent

OBD-II Trouble Code Technical Description

Vehicle Speed Sensor A Intermittent

What does that mean?

This diagnostic trouble code (DTC) is a generic powertrain code, which means that it applies to all 1996-newer vehicles (Porsche, BMW, Ford, Cadillac, Volvo, Mini, Chevy, Chrsyler, Toyota, etc.). Although generic, the specific repair steps may vary depending on make/model.

When a stored code P0503 is exhibited, it means that the powertrain control module (PCM) has detected a voltage input signal, from vehicle speed sensor (VSS) A, that is intermittent, erratic, or excessive. The designation A usually refers to the primary VSS in a system which utilizes multiple vehicle speed sensors.

 

OBD II vehicle speed sensors are typically electromagnetic sensors which utilize some type of toothed reluctor ring wheel or gear that is mechanically affixed to an axle, transmission/transfer case output shaft, differential gear, or driveshaft. As the shaft spins, so spins the metal reluctor ring. The reluctor ring completes a circuit with the stationary electromagnetic sensor as the reluctor passes in very close proximity to electromagnetic tip of the sensor. The notches between the teeth of the reluctor ring create interruptions in the sensor circuit. The combination of circuit completions and interruptions are recognized by the PCM (and possibly other controllers) as voltage wave form patterns.

Vehicle speed is monitored by the PCM using input data from one or more vehicle speed sensors. The PCM compares inputs from the VSS with antilock brake control module (ABCM) or electronic brake control module (EBCM) inputs. The primary VSS input (A) will likely be initiated by the VSS in the transmission but secondary VSS input/s may be monitored using one or more wheel speed sensors.

A typical VSS or vehicle speed sensor:

If the PCM detects an intermittent, erratic, or high input voltage signal from the primary VSS, a code P0503 will be stored and a malfunction indicator lamp may be illuminated. An intermittent, erratic, or high voltage input condition may be the result of an electrical or mechanical problem.

Related vehicle speed sensor trouble codes:

P0500 Vehicle Speed Sensor "A" Malfunction P0501 Vehicle Speed Sensor "A" Range/Performance P0502 Vehicle Speed Sensor "A" Low Input

Code Severity & Symptoms

Since conditions which may result in a stored code P0503 could create drivability and ABS issues, it should be classified as severe and addressed with some degree of urgency.

Symptoms of a P0503 code may include:

Erratic speedometer/odometer operation Irregular transmission shift patterns Other transmission and ABS codes may be stored Illumination of the service engine soon lamp, traction control lamp, or antilock brake lamp Unexpected activation/deactivation of the traction control system (if equipped) The ABS system may be rendered inoperable in some cases

Causes

Possible causes for this code include:

Excessive metal debris buildup on speed sensor/s A defective wheel speed or vehicle speed sensor Cut or otherwise damaged wiring harnesses or connectors (especially near speed sensors) Damaged or worn teeth on a reluctor ring A faulty PCM, ABCM, or EBCM

Diagnostic and Repair Procedures

I would require a diagnostic scanner, a digital volt/ohmmeter (DVOM), possibly an oscilloscope, and a reliable vehicle information source to diagnose a code P0503. A scanner with an integrated DVOM and oscilloscope would be ideal for this diagnosis.

I like to start my diagnosis with a visual inspection of system wiring, speed sensors, and connectors. I would repair open or shorted circuits as required and clean excessive metallic debris from effected sensors. If sensor removal is feasible, I would also check the integrity of the

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