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2017 Audi A6 ABS/ESC Light On - C0040 Wheel Speed Sensor?

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Mike T. · rep 0 · May 25, 3:10 AM · 1 replies · solved · Question

Vehicle: 2017 Audi A6 3.0T Prestige

Hi everyone,

I'm having an issue with my 2017 Audi A6 3.0T Prestige. Lately, both the ABS and ESC (Electronic Stability Control) warning lights have been illuminated on my dashboard. It started intermittently but now they're on constantly.

I scanned the car with my VCDS, and it's showing a C0040 code, which points to a 'Right Rear Wheel Speed Sensor' fault. I've read that these sensors can go bad, or sometimes the wiring gets damaged.

Has anyone experienced this specific issue on an A6 of this generation? Is it usually just a matter of replacing the sensor, or should I be looking for something else like wiring damage or even an ABS module issue? I'd like to try and tackle this myself if it's straightforward.

Thanks for any help!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 3:10 AM

0

ClearTheCode admin answer:

A C0040 code indicating a 'Right Rear Wheel Speed Sensor' fault on your 2017 Audi A6 is a very common diagnostic trouble code for ABS and ESC system warnings. These sensors are crucial for various vehicle systems, including ABS, traction control, stability control, and sometimes even cruise control.

Here's a breakdown of the likely causes and troubleshooting steps:

  1. Faulty Wheel Speed Sensor:

    • Cause: The sensor itself can fail due to internal electrical issues, corrosion, or physical damage. This is the most common cause for a specific wheel speed sensor code.
    • Diagnosis: You can often test the sensor's resistance with a multimeter (refer to service manual specifications for your A6). A more definitive test involves monitoring the sensor's live data output with a scan tool while rotating the wheel. If it shows an inconsistent or no reading compared to other wheels, it's likely faulty.

  2. Damaged Wiring or Connector:

    • Cause: The wiring harness leading to the right rear wheel speed sensor can get damaged from road debris, rubbing, or corrosion at the connector pins. This can interrupt the signal.
    • Diagnosis: Visually inspect the entire length of the wiring from the sensor to where it enters the body. Pay close attention to areas where it might rub against suspension components or the chassis. Check the connector for bent pins, corrosion, or looseness.

  3. Tone Ring/ABS Ring Damage:

    • Cause: The tone ring (also known as the ABS ring or reluctor ring) is a toothed wheel that the sensor reads. If it's cracked, corroded, or has missing teeth, the sensor won't get an accurate signal.
    • Diagnosis: This usually requires removing the wheel and sometimes the brake rotor to visually inspect the tone ring, which is often integrated into the wheel bearing or axle shaft.

  4. ABS Module Malfunction (Less Common for Specific Sensor Code):

    • Cause: While possible, an ABS module failure typically triggers multiple codes or a general communication fault, rather than a single wheel speed sensor code. However, it's not entirely impossible.
    • Diagnosis: This is usually a last resort if all other checks come back clear and requires specialized diagnostic tools and expertise.

When to see a shop:

  • If you've replaced the sensor and thoroughly inspected the wiring, but the code persists.
  • If you suspect tone ring damage that requires significant disassembly.
  • If you lack the tools or confidence to perform electrical diagnostics or component replacement.

It's important to address ABS/ESC faults promptly, as these systems are critical for vehicle safety and handling, especially in adverse conditions.

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