Technical Description of OBD-II Trouble Code
Range/Performance Issue with Vehicle Speed Sensor “A”
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to OBD-II equipped vehicles, including Honda, Proton, Kia, Dodge, Hyundai, VW, Jeep, and others.
While it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
What does this mean?
In simple terms, a P0501 trouble code indicates that the vehicle’s speed, as detected by the Vehicle Speed Sensor (VSS), is outside the expected range (either too high or too low). The VSS input is used by the vehicle’s main computer, known as the PCM/ECM powertrain/engine control module, along with other inputs to ensure proper operation of the vehicle systems.
How does the VSS work?
Typically, the VSS is an electromagnetic sensor that utilizes a rotating reluctor ring to complete an input circuit to the PCM. The VSS is positioned in the transmission housing in close proximity to the reluctor ring, which is attached to the transmission’s output shaft and spins along with it.
As the reluctor ring passes by the electromagnetic tip of the VSS, the circuit is rapidly completed and interrupted by notches and grooves. The PCM recognizes these circuit manipulations as transmission output speed or vehicle speed.
A typical VSS or vehicle speed sensor:
Related trouble codes for the vehicle speed sensor:
Potential Symptoms
This code differs from the P0500 code in that it may not trigger the malfunction indicator light (MIL). The potential symptoms are essentially the same as those for the P0500 VSS code:
Causes
A P0501 DTC trouble code may be caused by one or more of the following:
Diagnostic & Repair Steps
As a vehicle owner or DIYer, a good initial step is to search for technical service bulletins (TSBs) specific to your vehicle’s make, model, engine, and year. If a known TSB exists (as is the case for certain Toyota vehicles), following the instructions in the bulletin can help save time and money in diagnosing and repairing the issue.
Next, visually inspect all wiring and connectors that lead to the speed sensor. Thoroughly examine for any chafing, bare wires, broken wires, melted areas, or other damage. Repair as necessary. The location of the sensor depends on the vehicle and may be on the rear axle, transmission, or wheel hub (brake) assembly.
If the wiring and connectors appear to be in good condition, proceed to check the voltage at the speed sensor. The exact procedure will vary based on the vehicle’s make and model.
If everything appears to be in order, replace the sensor.
