P0503: Vehicle Speed Sensor A Circuit Intermittent/Erratic/High

The vehicle speed signal A comes, depending on the maker, from a sensor on the gearbox, the transmission output speed, the wheel speeds via ABS/ESP or a CAN message; CARB explicitly names it as an input to be monitored. P0503 combines three fault patterns: sporadic signal loss, jumping values and a value that is too high. GM detects a sudden signal drop quickly (0.3 s, 5 counts, MIL on the first trip); Subaru sets it at 240 km/h or more for a cumulative 4 s, Saab's diesel above 220 km/h. In limp mode Subaru sets the speed to zero, disables fuel cut-off on overrun and raises the fan.

Symptoms

• Check engine light on
• Speedometer needle jumps
• Cruise control drops out, jerky shifting

Most likely causes

• Loose contact, chafed wire, corroded connector
• Interference from damaged shielding or the ignition
• Sensor with weakened magnet or damaged tone wheel
• ABS/ESP fault (signal source)

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the speed in live data while someone else drives
2. Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
3. Inspect the connector and wiring
4. Read the ABS codes as well
5. Replace the sensor if there is no signal

Good to know

• Repair difficulty: medium
• It can trigger limp mode.
• It affects emissions.

What each character of P0503 means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• 5: Speed and idle
• 03: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0503?

Drive with caution: the speedometer may be wrong and driver assistance features may fail.

What causes code P0503?

The most common causes are: loose contact, chafed wire, corroded connector; interference from damaged shielding or the ignition; sensor with weakened magnet or damaged tone wheel.

Related codes

• P0500Vehicle Speed Sensor A Circuit
• P0501Vehicle Speed Sensor A Circuit Range/Performance
• P0502Vehicle Speed Sensor A Circuit Low
• P0723Output Shaft Speed Sensor Circuit Intermittent
• P0720Output Shaft Speed Sensor Circuit

Sources

• gsi.ext.gm.com: 18OBDG03A Engine Diagnostics
• saabwisonline.com: dtc p0503 vehicle speed sensor intermittent errati
• saabwisonline.com: p0500 p0501 p0503

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.