Experiencing a check engine light with the OBD2 code P0500 can be frustrating. Often labeled as a “Vehicle Speed Sensor” issue, the diagnosis isn’t always straightforward, especially in Subaru vehicles. This guide, based on real-world experience, will help you navigate the complexities of the P0500 code and potentially save you time and money on unnecessary repairs.
Understanding the P0500 Code in Subaru Vehicles
It’s a common misconception that the P0500 code in Subarus directly points to the speed sensors located in the transmission. In reality, for Subaru models like the Tribeca, Outback, and Legacy, the P0500 code is often related to the Anti-lock Braking System (ABS) and Vehicle Dynamics Control (VDC) system. This means the problem might lie within your wheel speed sensors, which are part of the ABS system, rather than the transmission speed sensors themselves.
To get a clearer picture, simply reading the standard Obd2 P0500 code isn’t enough. You’ll need to delve deeper and retrieve secondary codes, specifically the cruise control codes (C-codes), to pinpoint the exact issue.
Diagnosing P0500: Reading ABS/VDC Cruise Control Codes
While generic OBD2 scanners can pull the P0500 code, they usually fall short when it comes to reading the crucial C-codes from the ABS/VDC module. Attempting to use the standard Subaru diagnostic code reading method (key cycling) for C-codes will likely result in a flashing “C—-” – indicating the module isn’t responding without the engine running.
The most effective way to access these C-codes is by using specialized software like FreeSSM and a Vag-com OBD2 cable. These cables are readily available online at affordable prices.
Here’s how to use FreeSSM to retrieve the necessary codes:
- Acquire a Vag-com KKL 409.1 OBD2 cable.
- Download and install FreeSSM software.
- Connect the cable to your vehicle’s OBD2 port and your computer.
- Start your vehicle’s engine. This is crucial as the ABS/VDC module needs to be active.
- Run FreeSSM and navigate to the “Cruise Control” tab within engine diagnostics.
- Read the displayed C-codes. Ignore any initial C0043 code if you checked with the engine off; this is a generic “cancel code” and not relevant to the actual problem.
By following these steps, you can extract the specific C-codes that will guide you towards the faulty wheel speed sensor or related component causing the P0500 error.
Case Study 1: Damaged ABS Wheel Speed Sensor and Tone Ring
One common scenario involves a damaged ABS wheel speed sensor. After pulling the C0023 code using FreeSSM, which indicated an issue with the front left wheel speed sensor, a DIYer inspected the sensor and found it visibly damaged.
The damage wasn’t just to the sensor itself. Upon closer inspection, the magnetic tone encoder ring on the back of the hub assembly was also found to be the culprit, causing the sensor damage.
Initially, replacing both the hub assembly and the speed sensor seemed like the obvious solution. However, even after this replacement, the P0500 code persisted. This highlights a critical lesson: don’t just throw parts at the problem without thorough diagnosis.
Further investigation, referencing the Factory Service Manual (FSM) for code C0023, led to testing the voltage to the speed sensor and checking wiring continuity. In this case, the wiring was sound, but the initial parts replacement was based on an incomplete diagnosis.
Case Study 2: The Unexpected Dust Shield Interference
In another instance of P0500 diagnosis on a Subaru Tribeca, an Autel scanner revealed a “Left Front ABS Sensor Circuit Open” code. Replacing the sensor seemed logical, but the issue remained. During sensor replacement, a keen observation revealed the real culprit: a warped dust shield.
While rotating the brake rotor after removing the sensor, a piece of metal was seen moving with the axle, intermittently blocking the sensor gap. This turned out to be the dust shield, which had rusted and deformed, being pushed towards the wheel bearing by the CV axle. This interference was physically damaging the ABS sensor and causing the circuit issue.
The solution in this case involved replacing the axle to address the dust shield issue, along with a new ABS sensor. This case underscores the importance of looking beyond the obvious sensor failure and considering peripheral components that can cause P0500 errors.
Key Takeaways for Diagnosing P0500
When tackling a P0500 code on your Subaru:
- Don’t assume it’s a transmission speed sensor. Focus on the ABS/VDC system and wheel speed sensors.
- Read ABS/VDC C-codes using FreeSSM and a Vag-com cable. This will provide specific fault codes beyond the generic P0500.
- Visually inspect the ABS wheel speed sensors and tone rings. Look for physical damage, debris, or corrosion.
- Consider less obvious culprits like dust shields. Check for deformation or interference, especially in older vehicles prone to rust.
- Diagnose thoroughly before replacing parts. Use a Factory Service Manual (FSM) for guided troubleshooting steps related to specific C-codes.
By taking a systematic approach and utilizing the right tools and knowledge, you can effectively diagnose and resolve P0500 Vehicle Speed Sensor issues in your Subaru, getting you back on the road with confidence.
