C0668 — Right Rear Wheel Speed Sensor B Circuit Low

OBD2 code C0668 flags a problem with the ABS / stability control (C0668 — right rear wheel speed sensor b circuit low: causes, symptoms & fix). Short, gentle driving to a shop is usually possible. Common culprits: faulty ABS module or pump motor, damaged tone (reluctor) ring on the hub, blown fuse or low voltage to the ABS module.

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Is it safe to drive?

Drive with caution The base brakes usually still work, so careful driving is possible — but ABS and stability control are disabled, which lengthens stopping distances on slippery roads. Fix promptly and avoid harsh driving.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm C0668 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many C0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the ABS / stability control for damage, corrosion, chafing or poor contact.
Subsystem check Read all four wheel speed PIDs while driving slowly — the faulty sensor drops out or reads implausibly.
Subsystem check Inspect the sensor and tone ring for metal debris and damage near the hub.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm C0668 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for C0668 (parts and labor, USD, independent shop rates): Replace a wheel speed sensor: $120–$350; Repair sensor wiring: $80–$250; ABS module repair or replacement: $400–$1,200. Overall, fixing C0668 usually costs between $80 and $1,200. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

Will C0668 clear itself?

Sometimes C0668 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

What does OBD2 code C0668 mean?

How much does it cost to fix C0668?

Replace a wheel speed sensor — $120–$350; Repair sensor wiring — $80–$250; ABS module repair or replacement — $400–$1,200. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

What is the most common cause of C0668?

The most common causes are: faulty ABS module or pump motor, damaged tone (reluctor) ring on the hub, blown fuse or low voltage to the ABS module.

Is it safe to drive with C0668?

The base brakes usually still work, so careful driving is possible — but ABS and stability control are disabled, which lengthens stopping distances on slippery roads. Fix promptly and avoid harsh driving.

C0668 — C0668 — Right Rear Wheel Speed Sensor B Circuit Low: Causes, Symptoms & Fix

When your scan tool pulls code C0668, it is telling you that the vehicle's ABS control unit has detected an abnormal signal from the right rear wheel speed sensor circuit. Specifically, C0668 indicates the circuit is reading lower than it should — a condition often described as "circuit low." This falls within the C0xxx family of chassis codes, which means the problem lives in the anti-lock braking or electronic stability control hardware rather than the engine or transmission.

The wheel speed sensors on each corner of the vehicle constantly feed rotation data back to the ABS module. That module uses the information to modulate brake pressure during an emergency stop, prevent wheel lockup, and help the stability system keep the car oriented correctly through a corner. When the signal from the right rear sensor drops below the module's acceptable threshold for multiple consecutive drive cycles, the unit stores C0668 and turns on the warning light. The freeze frame snapshot recorded alongside the code is particularly useful — it captures engine RPM, vehicle speed, coolant temperature, and other sensor readings at the exact moment the fault triggered, giving you a reliable starting point for your investigation.

Common symptoms of C0668

The most obvious sign that C0668 has set is the ABS or ESC warning lamp glowing on the instrument cluster. Beyond the light, drivers frequently notice that their speedometer behaves erratically or stops updating altogether, and adaptive cruise control may refuse to activate or shut itself off unexpectedly. The stability control system typically disables itself when this code is active, which means the instrument panel may display a "Stability Control Disabled" message. You might also feel a change in brake pedal behavior during normal stops — some owners report a subtle pulsation that was not present before. In severe cases, the anti-lock function does not engage at all during hard braking, leaving you with standard friction stopping power only.

What causes C0668

Wheel speed sensors sit in a harsh environment near each hub, exposed to road salt, moisture, and physical shock. The most frequent culprit behind C0668 is simply a worn or failed sensor — the internal circuitry degrades over time and stops producing a clean signal. A damaged tone ring (also called a reluctor ring) on the rear hub is another common cause; if the teeth are bent, missing, or coated with rust, the sensor cannot read them properly. Wiring problems rank third: the harness running from the sensor to the ABS module can chafe, melt against exhaust components, or suffer corrosion at the connector pins. In some vehicles, a blown fuse or insufficient voltage supply to the ABS module itself can mimic a sensor fault and trigger C0668. Less commonly, the ABS control unit or its internal pump motor is the root cause.

How to diagnose C0668

Start by connecting a quality OBD2 scanner, confirm that C0668 is stored in the ABS module, and record the freeze frame data before you clear anything. That snapshot tells you the vehicle speed, engine load, and temperature when the failure occurred, which helps you replicate the conditions during a test drive.

Next, pull any related trouble codes. Coexisting sensor codes, communication faults, or voltage-related codes often point to the actual problem faster than the sensor alone. Check whether your manufacturer has published a technical service bulletin for this specific code — many C0xxx issues have known factory fixes or require a module software update rather than a physical repair.

Visually inspect the right rear wheel well. Look closely at the sensor wiring harness for cracked insulation, rubbing against suspension components, and any signs of moisture intrusion at the electrical connector. Push the connector in firmly and check for bent or corroded pins.

With the scanner still connected, navigate to the live wheel speed PID screen and drive the vehicle slowly while watching the readings. A healthy sensor produces a smooth, increasing RPM value as speed rises. A faulty sensor drops out intermittently, freezes at zero, or spikes to an implausible number. Compare all four corners — the right rear should stand out.

If the wiring checks out, remove the sensor from the hub and examine the tone ring. Metal debris, rust buildup, or physical damage to the teeth will prevent accurate reading. Finally, clear the code, complete a drive cycle that mimics the freeze frame conditions, and verify C0668 does not return.

Repair options and cost

Once you have isolated the failure point, repair paths vary widely in cost. If the sensor itself is faulty, a replacement unit runs $120 to $350 for parts and labor at an independent shop. Wiring repairs — fixing a damaged harness, replacing a corroded connector, or splicing a broken wire — typically fall between $80 and $250. When the ABS control module itself is at fault, expect to pay $400 to $1,200 for repair or replacement, as this involves specialized electronics and programming.

Overall, the total bill for C0668 usually lands somewhere between $80 and $1,200 depending on which component failed. An accurate diagnosis before purchasing parts is the single most effective way to control costs, since the most expensive repair scenario is rarely where you should start.

Can you drive with C0668?

The standard friction braking system remains functional, so you can still stop the vehicle. However, both the anti-lock function and the electronic stability control are disabled while this fault is active. On wet pavement, ice, or gravel, stopping distances increase noticeably and the car cannot correct for a skid. Address this code promptly and drive conservatively until the repair is complete.