What C0040 means
The same fault as C0035 on the right-front corner: the ABS computer has lost a trustworthy speed signal from that wheel and has stood down the anti-lock, traction, and stability systems that depend on it.
What you’ll notice
- ABS + traction/stability lights
- Brakes normal, safety nets off
- Possible low-speed false ABS activation
Likely causes and repair cost
Broad US independent-shop bands, parts and labour.
Can you drive with C0040?
Same as its left-side twin: normal driving is fine; emergency-stop behaviour reverts to pre-ABS physics. Adjust following distances accordingly and fix it promptly.
The misdiagnosis to avoid
Replacing the sensor without inspecting the tone ring behind it. On many cars the ring rusts, swells, and cracks — destroying the new sensor's signal too. A corner that eats a second sensor had a ring problem all along; ask for the ring's condition with any sensor replacement.
Describe what it’s doing in your own words and the symptom checker gives you a safe-to-drive verdict, ranked causes with costs, and notes to take to the shop — free, no sign-up.
Read the code yourself
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Best for: Anyone who just wants to know what the light means
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Pairs with your phone and reads far more than engine codes — ABS, airbag, transmission and HVAC on most vehicles — plus live data. The real feature is the repair reports, which map a code to the fixes that most often resolved it on your specific year, make, model and engine. No subscription.
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The enthusiast pick. Faster live data than most dongles and it works with a wide range of third-party apps, which matters if you want custom dashboards or logging. Well regarded for connection stability and for not draining the battery when left plugged in.
Best for: People who want live data and app flexibility
Check price on AmazonQuestions people ask
Front sensors seem to fail more than rears — why?
Front corners live the hardest life: maximum brake heat, maximum road spray, and the most suspension and steering movement flexing the wiring. Front sensor codes outnumber rears at every shop, and it's environment, not coincidence.
Can I clean the sensor instead of replacing it?
Sometimes genuinely — a magnetic tip furred with brake-dust filings or a mud-packed mounting bore causes signal faults a careful cleaning cures. It's a legitimate first attempt during diagnosis; a sensor that's cracked, corroded internally, or reading weak on a scope is a replacement.