C05B3

Code

Generic C — Chassis

Brake Booster Temperature Sensor C Circuit Low

Brand: Generic

Type: C — Chassis

Views: UK: 24 EN: 40 RU: 27

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Short to ground on the sensor signal wire
Open or high-resistance connection in the sensor supply or signal circuit
Faulty brake booster temperature sensor (thermistor)
Corroded or damaged connector/terminal
Poor module ground or failed ABS/brake control module input
Water intrusion or physical damage to harness or sensor

Symptoms

Brake/ABS/ESC warning lamp illuminated or stored fault in brake control module
Brake assist logic may revert to fallback behavior (possible altered pedal feel in some vehicles)
Brake booster temperature reading stuck at a low value or abnormal temperature in live data
Possible limp-home mode or reduced functionality of related systems (ABS/ESC)

What to check

Retrieve freeze frame and stored data with a capable scan tool; record battery voltage and ambient conditions
Scan tool — observe live data for brake booster temperature (Circuit C) and compare with other temperature sensors and ambient temperature
Visually inspect sensor and wiring harness for damage, chafing, corrosion, and water intrusion at sensor and module connectors
Check connector pins for corrosion, bent pins, pushed-out terminals, or moisture
Measure reference supply voltage and ground at the sensor connector with ignition ON (backprobe)
Measure sensor signal voltage while monitoring live data and while applying temp change if possible (warm/cool sensor)

Signal parameters

Reference supply commonly 5.0 V (verify manufacturer spec)
Normal sensor signal typically within ~0.5–4.5 V depending on temperature (varies by design)
Circuit low condition often means signal voltage below ~0.1–0.3 V (manufacturer-specific threshold)
Typical thermistor resistance example (variation): ~10 kΩ at 25 °C — consult vehicle-specific data for exact values

Diagnostic algorithm

Use a scan tool to confirm C05B3 is active and view live brake booster temperature C value. Note battery voltage and other related fault codes.
Visually inspect sensor, booster, and harness. Repair any obvious damage or corrosion before electrical testing.
With ignition ON (engine OFF unless specified), backprobe the sensor connector and measure: reference voltage, sensor signal voltage, and ground continuity. Compare to vehicle specifications.
If reference voltage is absent or low, trace and repair supply circuit and module power/ignition feed. If ground is poor, repair ground connection.
If reference and ground are good but signal is low, disconnect the sensor and measure resistance of sensor element across its terminals. Compare to known resistance-vs-temperature chart for that sensor (if not available, compare to a known-good sensor if possible).
Check continuity between sensor signal wire and module input; look for shorts to ground (infinite/very low resistance to ground indicates short).
Perform a wiggle test on harness/connectors while observing live data to find intermittent faults.
If wiring and connector repair does not clear the fault and the sensor resistance/behavior is out of spec, replace the brake booster temperature sensor.
If new sensor still shows circuit low and wiring is verified, suspect module input fault; consult manufacturer service information before replacing module.
Clear codes, road test, and re-scan to confirm the repair and that the fault does not return.

Likely causes

Damaged sensor wiring harness rubbed through and contacting chassis ground
Corroded connector causing intermittent low voltage to sensor signal
Failed/shorted temperature sensor element (low resistance to ground)
Loose or corroded ground at ABS/brake module
Failed brake control module input stage (less common)

Fault status

⚠️ Status

Brake booster temperature sensor C signal is below expected range (circuit low). Check sensor, wiring for short to ground, connector corrosion, and module inputs.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours