P0502 Code: Vehicle Speed Sensor A Low Input

A P0502 code set by your vehicle’s powertrain control module indicates a possible issue with your vehicle speed sensor (VSS) or its circuit. This device monitors your vehicle speed so that the PCM can properly adjust functions, such as torque converter clutch lock up and shift scheduling.

The code P0502 is set once your PCM detects a low voltage signal from your VSS A. This usually refers to the primary sensor in vehicles that have more than one device installed. Read on to learn more about this trouble code.

What Does the P0502 Code Mean?

Diagnostic trouble code (DTC) P0502 stands for “Vehicle Speed Sensor A Low Input.” This code is applicable to select models from 1996 onwards.

Your vehicle makes use of a speed sensor to monitor rotational speed to estimate how fast the vehicle is going.  Most of these sensors are electromagnetic. They’re paired with a toothed reluctor ring wheel or gear that’s typically attached to the transmission/transfer case output shaft or differential gear.

The sensor sends data to the PCM using voltage signals. Once the PCM detects a low input voltage signal from VSS A, it can trigger the P0502 code. This issue can be electrical or mechanical in nature.

Note: The definition of code P0502 may be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.

What Are the Common Causes of the P0502 Code?

• Faulty VSS
• Metal debris build up on the speed sensor
• Wiring harness or connector issues
• Worn out reluctor ring teeth
• An issue with one of the vehicle’s control modules

What Are the Common Symptoms of the P0502 Code?

• Erratic speedometer/odometer operation
• Illuminated warning lights (check engine light, anti-lock brake light, etc.)
• Irregular transmission shift pattern
• Inoperative vehicles systems (anti-lock brake, traction control, etc.)

How to Diagnose the P0502 Code

DTC P0502 is a generic code that can be logged across several makes and models. However, this does not mean that there’s only one way to diagnose its underlying cause. The steps for troubleshooting this code will vary depending on the specific vehicle that you own.

You can check out these videos if you plan to work on your vehicle yourself:

How to Fix the P0502 Code

Symptoms and triggers of code P0502 may be similar across various vehicles. But that does not mean that the steps to get this issue fixed are the same for all. All vehicles are built differently. Make sure to check vehicle-specific repair procedures before doing anything with your vehicle. 
We recommend consulting the vehicle repair manual or an online repair database to learn the appropriate diagnostic and repair procedures for this code. If you’re not an experienced DIYer, we strongly advise leaving the job to a trusted mechanic.