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DTC codes / C05xx · Brakes, steering and suspension / C05B6

C05B6Brake Booster Temperature Sensor C Circuit Range/Performance

The C05B6 code indicates that the powertrain control module (PCM) or body control module (BCM) has detected an out-of-range or performance issue with the brake booster temperature sensor circuit, specifically the 'C' circuit. This sensor monitors the temperature of the brake booster to prevent overheating and ensure proper brake assist function, and the code sets when the sensor signal voltage or resistance falls outside the expected range for the current operating conditions.

SystemChassis
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaBrakes, steering and suspension

Symptoms you may notice

  • Illumination of the brake system warning light or a generic check engine light on the dashboard
  • Often no symptoms besides the warning light, as the brake system may still function normally
  • Reduced or inconsistent brake pedal assist, especially during repeated braking events
  • A soft or spongy brake pedal feel that may require extra effort to stop the vehicle
  • In rare cases, a burning smell or smoke from the brake booster area if overheating occurs
  • Possible activation of a limp mode or reduced power mode in some vehicles to protect the braking system

Common causes, most likely first

  1. Faulty brake booster temperature sensor or its internal thermistor element
  2. Damaged or corroded wiring harness or connector at the sensor or module
  3. Open or short circuit in the sensor signal or ground circuit
  4. Failed brake booster assembly causing abnormal temperature readings
  5. Corrosion or water intrusion into the sensor connector or wiring
  6. PCM or BCM software glitch or internal fault misinterpreting the sensor signal
  7. Aftermarket or incorrect sensor installed that does not meet OEM specifications

How to diagnose and fix it

  1. Use an OBD-II scanner to retrieve the code and check for any related freeze-frame data to understand the conditions when the fault set
  2. Visually inspect the brake booster temperature sensor, its connector, and wiring for damage, corrosion, or loose connections
  3. Measure the sensor resistance or voltage with a multimeter and compare to the manufacturer's specifications to verify sensor operation
  4. Check the continuity and resistance of the sensor signal and ground circuits between the sensor and the control module to rule out wiring faults
  5. If the sensor is faulty, replace it with a quality OEM or equivalent part and clear the code to see if it returns
  6. If the wiring and sensor are good, test the control module for proper voltage output and ground, and consider reprogramming or replacing the module if necessary
  7. Perform a road test with a scan tool to monitor live sensor data and confirm the repair before returning the vehicle to service

Hidden Causes of Brake Booster Sensor Codes

  • A common misdiagnosis is replacing the brake booster temperature sensor when the real problem is a chafed wire in the harness near the booster, often caused by engine vibration or heat damage.
  • The code can set intermittently due to a poor ground connection at the chassis, which affects the sensor reference voltage and mimics a sensor failure.
  • Some vehicles use the brake booster temperature sensor as part of a broader brake assist strategy, so a failing sensor may not trigger a noticeable symptom until the system enters a fail-safe mode.
  • After a brake booster replacement or engine work, the sensor connector may be inadvertently left unplugged or damaged, setting this code without any component failure.
  • A weak or failing battery or charging system can cause voltage spikes that disrupt sensor readings and set this code, so always check battery health before condemning the sensor.

Can I keep driving with C05B6?

It is generally safe to drive with this code if the brake pedal feels normal and no other warning lights are on, but avoid heavy braking or towing until the fault is repaired. If you notice reduced brake assist or a soft pedal, stop driving and have the vehicle towed to a repair shop.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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