10-02-2025
6 min.
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C0037 Left Rear Wheel Speed Sensor Circuit Malfunction

The C0037 Left Rear Wheel Speed Sensor Circuit Malfunction diagnostic trouble code indicates that the vehicle's Anti-lock Braking System (ABS) Control Module has detected an electrical problem in the left rear wheel speed sensor circuit.

Wheel speed sensors are essential components of modern vehicle safety systems. They continuously monitor the rotational speed of each wheel and send this information to the ABS module. The module uses this data to operate the Anti-lock Braking System (ABS), Electronic Stability Control (ESC), Traction Control System (TCS), Hill Start Assist, and several other advanced driver assistance systems.

When the ABS module detects an abnormal electrical condition such as an open circuit, short circuit, excessive resistance, intermittent signal, or invalid sensor output from the left rear wheel speed sensor, it stores the C0037 trouble code and usually illuminates the ABS warning light.

In most cases, the problem is related to the wheel speed sensor itself, damaged wiring, connector corrosion, a damaged tone ring, wheel bearing problems, or, less commonly, an ABS control module fault.

What Does C0037 Mean?

The left rear wheel speed sensor continuously measures the rotational speed of the left rear wheel.

The ABS module constantly monitors:

Wheel speed signal
Signal frequency
Circuit voltage
Circuit continuity
Sensor response time

If the module detects that the sensor signal is missing, unstable, outside the expected range, or electrically invalid, it stores DTC C0037.

Unlike performance-related wheel speed sensor codes, C0037 specifically indicates a circuit malfunction, meaning the issue usually involves the electrical circuit rather than the mechanical operation of the wheel itself.

How the Left Rear Wheel Speed Sensor Works

The wheel speed sensor is mounted close to a tone ring (reluctor ring) or a magnetic encoder built into the wheel bearing.

As the wheel rotates:

The tone ring passes the sensor.
The sensor generates an electrical signal.
The ABS module converts that signal into wheel speed.
The module compares the speed of all four wheels hundreds of times per second.

If one wheel suddenly slows faster than the others during braking, the ABS module reduces brake pressure to prevent wheel lockup.

The same wheel speed information is also used by:

Anti-lock Braking System (ABS)
Electronic Stability Control (ESC)
Traction Control System (TCS)
Electronic Brakeforce Distribution (EBD)
Hill Start Assist
Adaptive Cruise Control (on some vehicles)
Collision Avoidance Systems

Symptoms of C0037

The symptoms vary depending on the vehicle and the severity of the fault.

ABS Warning Light

The ABS warning light is usually the first indication that a problem exists.

Brake Warning Light

Some vehicles may also illuminate the brake warning light.

Stability Control Warning

The Electronic Stability Control (ESC) warning light may turn on.

Traction Control Disabled

Traction Control may stop functioning until the fault is repaired.

Cruise Control Problems

Certain manufacturers disable cruise control when wheel speed information becomes unreliable.

Driver Assistance Systems Disabled

Depending on the vehicle, the following systems may also become unavailable:

Adaptive Cruise Control
Automatic Emergency Braking
Collision Mitigation Braking
Hill Start Assist

No Noticeable Braking Problems

Under normal driving conditions, the hydraulic braking system usually continues operating normally.

However, ABS protection and electronic stability functions may no longer be available during emergency braking.

Common Causes of C0037

Several electrical and mechanical faults may trigger this diagnostic code.

Faulty Left Rear Wheel Speed Sensor

The sensor itself may fail because of:

Internal electronic failure
Water intrusion
Physical damage
Age-related deterioration

This is one of the most common causes.

Damaged Wiring Harness

The wiring leading to the sensor operates in a harsh environment.

Common wiring problems include:

Broken wires
Chafed insulation
Short circuits
Open circuits
Heat damage

Corroded or Loose Connector

Wheel speed sensor connectors are exposed to:

Water
Mud
Salt
Snow
Road debris

Corrosion or loose terminals can interrupt communication with the ABS module.

Damaged Tone Ring (Reluctor Ring)

Older vehicles typically use a toothed reluctor ring.

Possible failures include:

Cracked ring
Missing teeth
Rust expansion
Dirt buildup
Physical deformation

Damaged Magnetic Encoder

Many modern vehicles integrate the encoder inside the wheel bearing.

Possible failures include:

Magnetic strip damage
Contamination
Physical wear

Wheel Bearing Problems

A worn wheel bearing may:

Create excessive wheel movement
Alter the sensor gap
Damage the magnetic encoder

ABS Module Problems

Although less common, the ABS module itself may develop:

Internal circuit failures
Software issues
Communication faults

Vehicles Commonly Affected by C0037

C0037 is a generic OBD-II chassis code and may appear on a wide variety of vehicles equipped with ABS.

Examples include:

Ford F-150
Ford Explorer
Chevrolet Silverado
Chevrolet Equinox
GMC Sierra
Dodge Ram
Jeep Grand Cherokee
Toyota Camry
Toyota Corolla
Toyota RAV4
Honda Civic
Honda CR-V
Nissan Altima
Nissan Rogue
Hyundai Tucson
Kia Sportage
Volkswagen Golf
Audi A4
BMW 3 Series
Mercedes-Benz C-Class

Although the diagnostic code is generic, repair procedures may vary between manufacturers.

How C0037 Is Diagnosed

Proper diagnosis requires both electrical testing and inspection of mechanical components.

Read Stored Trouble Codes

A professional diagnostic scan tool should retrieve:

ABS fault codes
Stability control codes
Freeze-frame information

Related wheel speed sensor codes often help identify the source of the fault.

Monitor Live Wheel Speed Data

Technicians compare the live wheel speed readings from all four wheels.

The left rear sensor should closely match the speeds reported by the other wheels during normal driving.

Sudden dropouts, erratic readings, or a constant zero reading indicate a problem.

Inspect the Wheel Speed Sensor

The sensor should be checked for:

Physical damage
Dirt accumulation
Metal contamination
Proper installation

Inspect the Tone Ring or Encoder

Technicians inspect for:

Cracks
Rust
Missing teeth
Damaged magnetic encoder

Inspect Wiring and Connectors

Electrical inspection includes checking:

Continuity
Voltage
Ground
Connector condition
Corrosion
Loose terminals

Inspect the Wheel Bearing

Wheel bearings should be checked for:

Excessive play
Noise
Encoder damage

How to Fix C0037

The appropriate repair depends on the underlying cause.

Replace the Left Rear Wheel Speed Sensor

If testing confirms the sensor has failed internally, replacement is usually the correct repair.

Repair Damaged Wiring

Possible repairs include:

Repair broken wires
Replace damaged harnesses
Restore insulation

Repair or Replace Connectors

Corroded or damaged connectors should be cleaned or replaced.

Replace the Tone Ring

A damaged reluctor ring should be replaced to restore accurate wheel speed readings.

Replace the Wheel Bearing

If the magnetic encoder is integrated into the wheel bearing, the complete bearing assembly is usually replaced.

Clean the Sensor Area

Removing rust, mud, and metal debris may restore proper sensor operation.

Repair or Replace the ABS Module

If all other components test correctly, the ABS control module may require software updates, reprogramming, or replacement.

After repairs:

Clear the diagnostic trouble code.
Verify live wheel speed readings.
Perform a road test.
Confirm that C0037 does not return.

Can You Drive With C0037?

In most cases, the vehicle remains drivable because the conventional hydraulic braking system continues functioning.

However, the following systems may become unavailable:

Anti-lock Braking System (ABS)
Electronic Stability Control (ESC)
Traction Control System (TCS)
Brake Assist

Extra caution should be exercised on wet, snowy, or icy roads where these systems play an important role.

Is C0037 a Serious Code?

C0037 is generally considered a moderate safety-related diagnostic trouble code.

Although the vehicle usually remains operable, the loss of ABS and stability control can significantly reduce braking performance during emergency situations and on low-traction surfaces.

Prompt diagnosis and repair are recommended.

How to Prevent C0037

Regular maintenance can reduce the likelihood of wheel speed sensor failures.

Inspect Wheel Speed Sensors

Inspect the sensors periodically for damage or contamination.

Keep the Suspension Area Clean

Removing dirt and road debris helps protect the sensor and reluctor ring.

Inspect Wheel Bearings

Replace worn wheel bearings before encoder damage develops.

Protect Electrical Connectors

Inspect connectors regularly for corrosion, moisture intrusion, and loose terminals.

Address ABS Warning Lights Promptly

Early diagnosis often prevents more extensive ABS system repairs.

Final Thoughts

The C0037 Left Rear Wheel Speed Sensor Circuit Malfunction code indicates that the ABS control module has detected an electrical fault affecting the left rear wheel speed sensor circuit.

The most common causes include:

Faulty left rear wheel speed sensor
Damaged wiring
Corroded connectors
Damaged tone ring
Wheel bearing failure
ABS control module faults

A complete inspection of the wheel speed sensor, wiring, connectors, tone ring, wheel bearing, and ABS module is necessary to restore proper operation of the ABS, traction control, and stability control systems and ensure safe vehicle operation.