01 You Can Tell A Lot About A Car By Listening To Its Engine I… • 02 Why Your Car Shakes After Repairs and What It Really Means • 03 The Benefits of ABS: Why You Need This Safety Feature in Yo… • 04 Unlocking the Skies: A Comprehensive Guide to Thriving in t… • 05 This Is Why Your Car’s CV Axle Is Failing • 06 Hybrid Vehicles: How They Work and Their Pros and Cons • 07 P0045, P0046, P0047, and P0048: Turbo or Supercharger Boost… • 08 What is the Purpose of Hazard Lights and How to Use Them Pr… • 09 This Is How to Fix a Car That Won’t Start After Replacing t… • 10 Tesla Reveals The New Roadster And The First Thing Anyone N… •

DTC codes / C05xx · Brakes, steering and suspension / C05B5

C05B5Brake Booster Temperature Sensor C Circuit/Open

C05B5 indicates that the brake booster temperature sensor circuit C is open, meaning the control module sees an abnormally high resistance or a complete break in the wiring path for that sensor. The module uses this sensor to monitor the temperature of the brake booster, and an open circuit prevents it from receiving a valid signal, triggering the warning light and potentially disabling related brake assist functions.

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, often with no other noticeable symptoms.
  • Reduced or inconsistent brake pedal assist, especially during the first few presses after a cold start.
  • A stored trouble code in the anti-lock brake system (ABS) or body control module (BCM) that may not affect normal driving.
  • Intermittent warning light activation when driving over bumps or in wet conditions, indicating a loose connection.
  • In rare cases, a slight dragging or overheating smell from the brake booster area if the sensor fault masks a real temperature issue.

Common causes, most likely first

  1. A broken or chafed wire in the sensor circuit, often near the booster or where the harness flexes.
  2. Corroded or loose electrical connector at the brake booster temperature sensor.
  3. Failed brake booster temperature sensor itself, causing an open internal element.
  4. Damaged pins or terminals in the sensor connector or at the control module harness.
  5. Water intrusion into the connector or sensor, leading to corrosion and an open circuit.
  6. A faulty control module that incorrectly reports an open circuit despite good wiring (less common).

How to diagnose and fix it

  1. Inspect the sensor connector and wiring for obvious damage, corrosion, or loose pins, and clean or reseat as needed.
  2. Disconnect the sensor and measure resistance across its terminals; compare to the manufacturer's specification to confirm the sensor is open.
  3. Check continuity of each wire from the sensor connector to the control module, wiggling the harness to reveal intermittent opens.
  4. Perform a voltage drop test on the sensor circuit under load to identify high-resistance connections that a simple continuity test may miss.
  5. If wiring and sensor test good, substitute a known-good sensor or use a jumper to simulate a closed circuit and see if the code clears.
  6. Clear the code and perform a road test, including driving over rough surfaces, to verify the repair and ensure the warning light stays off.
  7. If the code persists after all circuit checks, follow the manufacturer's diagnostic flow for control module testing or replacement.

Why an open circuit is not always the sensor

  • A common mistake is replacing the brake booster temperature sensor without checking the harness, yet chafed wires near the booster or firewall cause most open-circuit codes.
  • The code can set intermittently due to a loose connector that only loses contact during vibration, so a static continuity test may pass while the fault remains.
  • On some vehicles, the brake booster temperature sensor shares a ground or reference voltage with other sensors, so an open in a shared wire can set multiple codes that mislead diagnosis.
  • A failed sensor may read open only when hot or cold, so testing resistance at room temperature alone can miss an intermittent internal break.
  • The control module may log this code if battery voltage was low during cranking, even though the circuit is intact, so always check for a weak battery before condemning parts.

Can I keep driving with C05B5?

The vehicle is generally safe to drive because the brake system retains normal hydraulic function, but you should avoid heavy braking or towing until the fault is repaired. If the brake pedal feel changes or the warning light flashes, stop driving and have the system inspected immediately.

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.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage