P0501 - OBD II Trouble Code
Vehicle Speed Sensor Range/Performance
Our emissions expert has put together the following information about the P0501 fault code. We have also included diagnostic procedures you can take to your repair shop if the mechanic is having difficulty analyzing the code.
OBD II Fault Code
- OBD II P0501
Fault Code Definition
- Vehicle Speed Sensor Range/Performance
- Check Engine Light will illuminate
- Vehicle may not shift properly
- Speedometer may not operate correctly
- In some cases, there are no adverse conditions noticed by the driver
- In some cases, there may be performance problems and/or shifting problems.
- Other warning lights may come on such as the ABS light and Traction Control light.
Common Problems That Trigger the P0501 Code
- Defective Vehicle Speed Sensor
- Defective Speedometer
- Vehicle Speed Sensor wiring or connector
- Communication (CAN) bus problems
- Defective transmission or differential Vehicle Speed Sensor drive gear
- Speedomter problem
- Internal Transmission problem
- ABS/Traction Control probelm
- Driveline problem
Polluting Gases Expelled
- HCs (Hydrocarbons): Unburned droplets of raw fuel that smell, affect breathing, and contribute to smog
- CO (Carbon Monoxide): Partially burned fuel that is an odorless and deadly poisonous gas
- NOX (Oxides of Nitrogen): One of the two ingredients that, when exposed to sunlight, cause smog
P0501 Diagnostic Theory for Shops and Technicians
When the code P0501 is set, it means that the Powertrain Computer or PCM isn't seeing a proper or "rational" signal from the Vehicle Speed Sensor. Write down the freeze frame data for the P0501 code and then, using a serial data capable scanner, take the vehicle on a test drive and duplicate the code setting conditions that were saved in the freeze frame data. Verify that there IS or is NOT a smooth steady signal coming from the VSS by finding and observing its data PID. If there is no VSS signal, I visually inspect the VSS and if it "looks" normal, I get a labscope waveform directly from the sensor. This has multiple advantages, because your bypassing the VSS wiring and connector. If the signal looks normal and steady then I would suspect a wiring/communication problem between the sensor and the PCM. If the sensor has a poor scope waveform, then you may have located the problem. I've also had instances where the signal is consumed by a component and the signal disappears or becomes too weak. I've seen an electronically defective speedometer or instrument cluster do this.