OBD Code P0500 Technical Definition & Details
The technical definition of onboard diagnostic (OBD) code P0500 relates to a "Vehicle Speed Sensor Malfunction".
P0500 is a generic powertrain code, which means it applies to your Alfa Romeo in roughly the same way it does to every vehicle sold in the US since 1996. Specific diagnostics & repairs tend to vary from vehicle to vehicle… this article focuses on steps to remedy the code on a Alfa Romeo.
What is a vehicle speed sensor malfunction?
The P0500 code indicates that the speed of the vehicle according to the Vehicle Speed Sensor (or VSS) appears to be incorrect or returning an unexpected value. VSS data is one of a wide range of diagnostics that the Powertrain Control Module (or Engine Control Module) uses to keep your vehicle operating correctly.
The VSS is an electromagnetically-actuated sensor that that uses a part called a "reluctor ring" mounted near the transmission's output shaft. This ring, in combination with the VSS itself, generate electricity that is in turn measured by the PCM. As the VSS sends data, the PCM crunches those numbers to determine your Alfa Romeo's speed.
OBD Code P0500 Symptoms on a Alfa Romeo
There are a wide range of annoying & potentially dangerous symptoms associated with P0500, including but not limited to ABS failure, an illuminated ABS warning light, a misbehaving or non-functional speedometer, incorrect behavior from the odometer, issues with automatic shifting, and trouble with the RPM limiter.
What causes P0500 on a Alfa Romeo?
There's not many things that can cause code P0500 on a Alfa Romeo – it's nearly always an issue with the VSS itself. However, it's also possible that the wiring between your Alfa Romeo's VSS & PCM is damaged. A huge range of things can cause wiring damage, from wild animals to excessive rubbing – so don't count it out!
Finally, if you've changed rim or tire sizes (perhaps with aftermarket parts), you'll likely be in need of VSS calibration to adjust your vehicle to the larger (or smaller) tires.
How to fix P0500 on a Alfa Romeo:
Visually inspect the wiring, connectors, etc that connect the speed sensor to the PCM. Look for any damaged, scuffing, chafing, or melted pieces. If you find some, you'll need to repair them, clear your codes, & you should be good to go. If you aren't seeing any damage, buy a Alfa Romeo Speed Sensor and replace the old one. If you are having a hard time finding the right sensor, go to your dealership & they should be able to help.
As a reminder, everything in the article above is provided on a best-effort basis & we can't take responsiblity for how you use the information container therin.