Diagnosing & Fixing P0500 ABS Sensor Malfunction in a 2018 Mercedes-Benz A-Class

Introduction

Imagine this: You’re driving your 2018 Mercedes-Benz A-Class, and suddenly, the ABS warning light appears on the dashboard. Shortly after, you notice the speedometer isn't working correctly, and your car’s handling feels off. You plug in an OBD-II scanner, and the fault code P0500 - Vehicle Speed Sensor Malfunction appears. What does this mean, and how do you fix it?

At AUTOTEK, we specialize in real-world diagnostics and vehicle troubleshooting. In this guide, we’ll explain why the ABS sensor has failed, how to diagnose it, and the best way to fix it.

Understanding P0500 – Vehicle Speed Sensor Malfunction

The ABS wheel speed sensors are critical for stability control, traction control, and speedometer accuracy. When a sensor like the right rear wheel speed sensor fails, your car’s ABS system can no longer determine the wheel speed accurately, leading to braking and stability issues.

Common Symptoms of a Failing ABS Sensor in a Mercedes A-Class:

• ABS & traction control warning lights activated
• Speedometer stops working or gives incorrect readings
• Braking feels inconsistent or unresponsive
• Reduced stability during wet or slippery conditions
• Faulty cruise control operation

Related ABS & Speed Sensor Fault Codes

A failing ABS sensor can trigger multiple diagnostic codes, including:

C003A - Right Rear Wheel Speed Sensor Circuit Malfunction

• Indicates a general issue with the sensor circuit.

C003A-1C - Right Rear Wheel Speed Sensor Signal is Implausible

• The signal from the sensor is outside the expected range, which may cause ABS failure.

C003A-31 - Right Rear Wheel Speed Sensor Open Circuit

• The ABS module is not receiving a signal from the sensor, possibly due to a broken wire or defective sensor.

C003A-4A - Right Rear Wheel Speed Sensor Signal Intermittent

• The sensor provides an inconsistent signal, often due to dirt, corrosion, or loose connections.

C0040 - Rear Wheel Speed Sensor Malfunction

• A general code indicating issues with one or both rear ABS sensors.

C0037 - ABS Wheel Speed Sensor Circuit Failure

• The ABS module has detected a problem with the entire wheel speed sensor circuit.

If any of these codes appear, it’s likely your right rear wheel speed sensor is faulty.

Step-by-Step Diagnosis of P0500 in a Mercedes-Benz A-Class

Before replacing the sensor, follow these diagnostic steps:

Step 1: Scan for Fault Codes

• Use an OBD-II scanner to confirm P0500 or related ABS codes.
• If additional codes like C003A-31 or C003A-4A appear, it indicates wiring or sensor failure.

Step 2: Inspect the ABS Sensor & Wiring

• Locate the right rear ABS sensor, near the wheel hub assembly.
• Inspect for damaged, corroded, or broken wires.
• Check for dirt or debris blocking the sensor.

Step 3: Test the ABS Sensor Signal

• Using a multimeter, measure the sensor’s resistance.
• A functioning ABS sensor should provide a steady voltage between 0.25V and 1.0V.
• If there’s no voltage output or fluctuating signals, the sensor is faulty.

Step 4: Check the ABS Ring (Reluctor Wheel)

• The ABS sensor reads the reluctor wheel’s teeth to detect wheel speed.
• If the reluctor wheel is damaged or misaligned, the sensor will not function correctly.

Step 5: Reset the Fault Code & Test Drive

• Clear the P0500 code using an OBD-II scanner.
• Start the engine and monitor the speed sensor readings.
• Take the vehicle for a test drive to check for warning lights.
• If the code reappears, the sensor likely needs replacement.

Recommended Fix for Mercedes-Benz P0500 Code

If diagnosing the system confirms an ABS sensor failure, the best solution is to replace the faulty sensor.

✅ Recommended Replacement Part: Rear Right ABS Sensor - Mercedes-Benz A-Class (W176) - 2465401305

Replacement Procedure:

1. Disconnect the battery to prevent electrical issues.
2. Raise the rear of the car and secure it with jack stands.
3. Locate the right rear ABS sensor near the wheel hub.
4. Unplug the sensor connector and remove any retaining bolts.
5. Install the new ABS sensor and reconnect the wiring.
6. Lower the car, reconnect the battery, and clear any stored fault codes.
7. Test drive the vehicle to ensure ABS functionality is restored.

Similar Fault Codes & Reference

If your vehicle displays additional ABS-related codes, here’s how they compare:

• C003A – Right Rear Wheel Speed Sensor Circuit Malfunction
• C003A-1C – Right Rear Wheel Speed Sensor Signal is Implausible
• C003A-31 – Right Rear Wheel Speed Sensor Open Circuit
• C003A-4A – Right Rear Wheel Speed Sensor Signal Intermittent
• C0040 – Rear Wheel Speed Sensor Malfunction
• C0037 – ABS Wheel Speed Sensor Circuit Failure

These codes all point to ABS sensor or wiring issues, which can often be resolved by replacing a faulty rear ABS sensor.

Conclusion

The P0500 fault code in a 2018 Mercedes-Benz A-Class is usually caused by a faulty right rear ABS sensor, leading to speedometer issues, ABS warning lights, and traction control failure. Replacing the faulty sensor can restore braking stability, fuel efficiency, and driving safety.

If you’re experiencing this issue, consider replacing the ABS sensor, available on AUTOTEK. Need expert guidance? Contact us for professional support.

Need More Help?

If you have any questions or need further assistance, our team at AUTOTEK is here to help! Leave a comment below or contact us directly.