What Does the Engine Code C0040 Mean?

When your car shows error code C0040, it means you have an issue with your right front wheel speed sensor.
Written by Joshua Levy
Reviewed by Melanie Reiff
If your car shows engine code C0040, you likely have a problem with your right front wheel speed sensor. While the code doesn’t typically indicate any dangerous problems, it could be caused by issues in the antilock braking system (ABS). Have your vehicle professionally diagnosed and repaired as soon as possible to avoid any major issues.  
Engine codes help car owners and professionals identify problems in their vehicles without manually inspecting every component. Unfortunately, engine codes don’t reveal the cause of the issue. You’ll likely need professional with an
OBD (On-Board Diagnostics) reader
help to identify the cause of the engine code.
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What does the engine code C0040 mean?

If your car shows engine code C0040, you probably have an issue with your right front wheel speed sensor
Each axel in your car has two speed sensors, one on each wheel, that track the wheel's speed. All the sensors report to the ABS module, which ensures all the wheels are turning at the same speed. If the ABS module notices any irregularities, your ABS warning light will go off.

How much will it cost to fix?

Diagnosing the problem will typically take around an hour, which should cost $75 to $150, depending on labor costs in your local auto shop. If you need to
replace the wheel speed sensor
, repairs could cost an additional $400.

What can cause the C0040 engine code?

Wheel speed sensors are made of a collection of magnets that track tire rotations. The sensors report the rotations to the ABS module, which interprets them as wheel speed. Engine code C0040 isn’t usually caused by major issues, but the problem could be serious if it results from a faulty ABS module.
Here are some of the most common causes of engine code C0040:
  • Faulty right front wheel speed sensor
  • Misaligned sensor magnets 
  • Broken ABS module

Common symptoms of the C0040 engine code

In general, the only symptoms of a C0040 engine code you should notice are illuminated ABS or stability/control lights. However, since these symptoms are typically associated with problems in the wheel speed sensor, you may notice the following symptoms when the warning code results from a faulty ABS module:
  • Lower traction control
  • Unresponsive brakes
  • Less stability
When engine code C0040 arises from problems in the ABS module, it could be dangerous. It’s best to have a professional diagnose and repair the issue as soon as possible. 

How serious is the C0040 engine code? 

Engine code C0040 is typically only dangerous when it results from a faulty ABS module. In this case, you could face major issues on the road like failing brakes, traction control, and stability control. 
If your car shows engine code C0040, have a mechanic diagnose and repair your vehicle as soon as possible. 

Can I fix the C0040 engine code myself?

It is possible to fix a C0040 engine code on your own, but it’s best to let a professional fix the issue. Whether the problem results from the right wheel speed sensor or the ABS module, the repair will involve knowledge of the following:
  • Your car’s electrical system
  • How the wheel sensor connects to your engine control module (ECM)
Since these elements of the repairs require an in-depth knowledge of your vehicle, it’s best to have a professional handle them.

Finding insurance for your vehicle

Repairing your wheel sensor can be expensive, but you can always offset the cost by saving on
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