2018 Mazda 6 ABS and Traction Control Lights On - OBD Codes C0034 and C0037

ClearTheCode admin answer:

It's quite common for the ABS and Traction Control lights to illuminate together, as the TCS system relies heavily on the same wheel speed sensor data as the ABS. The codes C0034 and C0037 specifically point to issues with the rear wheel speed sensors.

1. Inspect the Wheel Speed Sensors and Wiring:
   • Visual Inspection: Start by visually inspecting both the right and left rear wheel speed sensors and their wiring harnesses. Look for any signs of physical damage, corrosion, frayed wires, or loose connections. These sensors are often exposed to road debris and can get damaged.
   • Sensor Location: The wheel speed sensors are typically mounted near the wheel hub, reading a tone ring on the axle or hub assembly.
2. Check Tone Rings: The tone rings (or reluctor rings) are what the sensors read. Check them for damage, cracks, or excessive rust/debris buildup that could interfere with the sensor's reading. Sometimes, a build-up of metallic dust can cause issues.
3. Clean Connections: Disconnect the electrical connectors for both rear wheel speed sensors and clean them thoroughly with electrical contact cleaner. Reconnect them firmly.
4. Multimeter Test (Advanced): If you have a multimeter, you can test the resistance of the sensors (if they are passive sensors) or check for a signal (if they are active Hall-effect sensors, which are more common in newer vehicles). This usually requires specific resistance values or a scope to check the signal, so consult your service manual.

Potential Causes (beyond just the sensors):

• Wiring Harness Damage: Since both rear sensors are throwing codes, it's possible there's a common wiring harness issue affecting both, perhaps where the harness splits off to each side, or a ground issue.
• ABS Module: While less likely to throw specific sensor codes for both rear sensors simultaneously without other symptoms, a faulty ABS control module could theoretically cause incorrect readings. However, this is usually indicated by other, more general ABS module codes.

When to See a Shop:

If a thorough visual inspection, cleaning, and connection check don't resolve the issue, or if you're uncomfortable performing the diagnostic steps, it's best to take your Mazda 6 to a professional. A dealership or an independent shop with advanced diagnostic equipment can perform live data readings from the wheel speed sensors while driving, which can definitively determine if the sensors are faulty, if there's a wiring break, or if the ABS module is at fault. They can also check for voltage drops and continuity in the wiring.