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DTC codes / C05xx · Brakes, steering and suspension / C057D

C057DBrake Booster Temperature Sensor Circuit B Intermittent/Erratic

The C057D code indicates that the brake booster temperature sensor circuit B is sending an intermittent or erratic signal to the control module. The computer detects this when the sensor's voltage readings jump unpredictably or drop out momentarily, rather than following a smooth, expected pattern during normal brake operation.

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.
  • Intermittent or flickering warning light that may come and go with temperature changes or vibration.
  • Reduced or inconsistent brake assist, requiring more pedal effort in some cases.
  • A stored code in the module with possible related codes for the brake booster system.
  • In rare cases, the vehicle may enter a limp mode affecting brake performance or disable certain driver-assist features.

Common causes, most likely first

  1. A faulty brake booster temperature sensor with an internal intermittent connection or degraded thermistor element.
  2. Damaged or corroded wiring harness at the sensor connector, often due to heat exposure or road debris.
  3. Loose or backed-out terminals in the sensor pigtail, causing an erratic electrical connection.
  4. Chafed or shorted wires along the circuit path between the sensor and the control module.
  5. A failing control module with an intermittent internal fault in the sensor input circuit.
  6. Extreme temperature fluctuations causing temporary sensor signal instability, especially in high-heat braking conditions.

How to diagnose and fix it

  1. Inspect the sensor connector and wiring for corrosion, loose pins, or physical damage, and clean or repair as needed.
  2. Perform a wiggle test on the harness while monitoring live sensor data to reproduce the intermittent signal.
  3. Check the sensor's resistance or voltage output against the manufacturer's specification when cold and at operating temperature.
  4. Verify the integrity of the circuit from the sensor to the control module, looking for opens, shorts, or high resistance.
  5. Replace the brake booster temperature sensor if it fails the electrical tests or shows erratic behavior during monitoring.
  6. Clear the code and perform a road test with live data to confirm the repair and ensure the code does not return.
  7. If the code persists after sensor and wiring repairs, diagnose the control module for internal faults before replacement.

What most technicians overlook on C057D

  • A common misdiagnosis is replacing the brake booster assembly when the actual fault is a chafed wire near the exhaust or a loose connector pin that only acts up when hot.
  • The code can be set by a momentary voltage spike from a failing alternator or a poor ground connection, so always check charging system stability and ground straps before condemning the sensor.
  • Intermittent codes often leave no freeze-frame data, so using a scan tool with live data graphing is essential to catch the erratic signal in real time.
  • Some vehicles use the brake booster temperature sensor as part of a broader brake assist strategy, and a faulty sensor can cause subtle changes in pedal feel that drivers may not immediately connect to the warning light.
  • The sensor's thermistor can degrade gradually, producing a signal that stays within range at first but becomes erratic only under sustained braking or high ambient temperatures, so a simple resistance check at room temperature may pass.

Can I keep driving with C057D?

The vehicle is generally safe to drive if the brake pedal feels normal and the warning light is intermittent, but avoid heavy braking or towing until the fault is repaired. If the brake pedal becomes hard or braking performance drops, 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.

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