What the P0503 code means
The P0503 code indicates that the Engine Control Module (ECM) has detected an inconsistent signal voltage from the vehicle speed sensor.
What are the causes of the P0503 code?
A faulty vehicle speed sensor
Damaged wiring or connectors in the vehicle speed sensor circuit
Multiple faulty wheel speed sensors/ hub bearings
Broken ABS tone rings
A faulty ECM
Incorrect size wheels or tires
A faulty instrument cluster
What are the symptoms of the P0503 code?
Check Engine Light illumination
Speedometer needle may bounce up and down
Inaccurate speedometer
How does a mechanic diagnose the P0503 code?
Makes sure that the correct wheels and tires are installed
Locates the vehicle speed sensor then checks the connectors and the wiring in the circuit
If all is well so far:
Tests the vehicle speed sensor for faults using the manufacturer’s recommended procedure
In the unlikely event that the issue has not been found yet:
Inspects the wheel speed sensors
Inspects the tone rings
Inspects the wheels and tires
Inspects the ECM for faults
If any issues were found during the diagnosis of this issue, the parts would be replaced at the customer’s request.
Common mistakes when diagnosing the P0503 code
A common mistake that could be made when diagnosing the P0503 trouble code would be overlooking the obvious. Checking the wheels and tires for correct size is the first thing that should be done considering that it is a visual check and requires no tools other than your eyes.
How serious is the P0503 code?
The P0503 trouble code is not too serious. This code only affects the performance of the vehicle’s speedometer. The only issue that may occur while having a P0503 code would be a speeding ticket.
What repairs can fix the P0503 code?
Replacing the speed sensor
Repairing or replacing wiring or connectors in the speed sensor circuit
Replacing one or more wheel speed sensors
Replacing a hub bearing
Replacing a CV axle due to a faulty tone ring
Replacing the ECM
Replacing the instrument cluster
Fitting the correct size wheels and tires to the vehicle
Additional comments regarding the P0503 code?
If a P0503 trouble code is stored in your vehicle, it would be wise to drive slightly slower than the rest of traffic to ensure that you are not speeding until the issue has been resolved.
