OBD-II Trouble Codes

C0040 Code: Right Front Wheel Speed Circuit Malfunction

Reading Time: 4 minutes

Modern vehicles come with an enhanced braking system called the anti-lock braking system (ABS). This system uses sensors to warn the powertrain control module (PCM) of a panic stop situation. The ABS system then pulses the brakes to prevent wheel lockup. It is an important system that ensures the safety of the passengers and cargo inside a vehicle.

ABS sensors also get called wheel speed sensors. The ABS code C0040 is a diagnostic trouble code (DTC) that warns of a potential malfunction in one of the wheel speed sensors or the sensor’s circuit. This short but informative guide will help you understand this trouble code and its potential causes better.

What Does the C0040 Code Mean?

The C044 code stands for “Right Front Wheel Speed Circuit Malfunction.” Before proceeding with the definition of this code and what sets this code, keep in mind that the definition of OBD-Ii codes will differ depending on the make and model of your vehicle. It’s a good practice to refer to a repair manual or database for accurate information and repair guidelines for this trouble code and other codes that may also get stored in your vehicle’s memory.

The wheel speed sensors, also referred to as WSS or ABS sensors, are used to measure the wheel speed. There are usually four wheel speed sensors in a vehicle—one for each wheel. This is because the wheels of a vehicle do not always turn at the same speed.

Older wheel speed sensors are usually located outside the wheel hub. However, you can often find modern wheel speed sensors in the wheel hub assembly. The wheel speed sensors have a toothed ring called a reluctor and a magnet enclosed within a coil.

The reluctor is mounted on either the axle shaft or the wheel hub and rotates with the wheel assembly. Typically, wheel speed sensors produce a voltage in relation to a magnetic field which changes as the wheel rotates. The frequency and amplitude of the signal produced by the sensor increases as the wheels turn faster.

wheel hub with abs sensor
Older wheel speed sensors are usually located outside the wheel hub. However, you can often find modern wheel speed sensors in the wheel hub assembly.

The information that the sensors generate is used by the ABS computer or module to control the ABS system. It may also be used by other modules, however, this depends on the make and model of the vehicle.

The C0040 code sets when the ABS module notices that there is an issue with the right front wheel speed sensor or its circuitry.

Note: The definition of code C0040 may be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.

What Are the Possible Causes of the C0040 Code?

As with most OBD-II codes, there are multiple possible reasons why the code C0040 may register in your vehicle’s memory. Below are just some of these causes:

What Are the Common Symptoms of the C0040 Code?

abs warning light on
An illuminated ABS light is a common symptom of the C0040 code.

If you’re dealing with the C0040 code, you might deal with the following signs and symptoms as well.

How to Diagnose the C0040 Code

Troubleshooting OBD-II codes such as the code C0040 may sound intimidating, but it helps if you have the proper tools and information sources.

As a seasoned DIYer, you may refer to a handy repair manual or database for information. Consulting professional mechanics and technicians help, too. There are other sources and guides out there you can use for more information. Below is a helpful video resource on the C0040 code that you can use:

How to Fix the C0040 Code

There is no one-size-fits-all solution for OBD-II codes such as the C0040 because vehicles have different configurations and repair instructions, depending on their make and model. However, C0040 repair doesn’t have to become complicated, as there are a lot of resources available such as repair manuals and databases. If you’re not that confident in your own repair skills, you might want to leave the repairs to a professional so you can avoid more issues down the line.

Other Notes About C0040

C0040 has high repair importance and difficulty level. This means that an amateur DIYer may lack the ability to address the issue properly without the proper tools and information. Problems with the wheel speed sensor may not affect your brake function, but it can affect handling in wet, slick, or icy road conditions. This is because the wheel speed sensors are also a primary input to the traction control and stability control systems.

To prevent any further damage to the sensor or its related components, be vigilant and quick to address the issue immediately.

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