C05B4

Code

Generic C — Chassis

Brake Booster Temperature Sensor C Circuit High

Brand: Generic

Type: C — Chassis

Views: UK: 26 EN: 31 RU: 30

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Open or broken wiring between sensor and control module (pull-up causes high reading)
Short or accidental connection to battery positive (12V) on the sensor circuit
Poor or corroded connector or pins at the sensor or module
Failed temperature sensor (internal short/open or internal fault)
Faulty control module input (rare)
Water ingress or contamination in connector causing incorrect voltage

Brake system warning, ABS or traction-control warning lamp illuminated
Brake assist or system may enter degraded mode (reduced braking assistance)
Diagnostic trouble code C05B4 stored in ABS/Brake control module
Possible change in brake pedal feel if the booster depends on the sensor for control logic
Intermittent or persistent warning messages related to braking temperature/systems

Retrieve freeze-frame and live data with a capable scan tool; note sensor voltage/temperature values
Visually inspect sensor connector and harness for corrosion, damage, chafing or water
Backprobe sensor connector with key on (engine off) and measure voltage at sensor signal pin
Measure resistance of sensor (if service manual specifies) and compare to specification
Check for short to battery voltage or short to ground at the sensor harness (with connector disconnected)
Wiggle wiring harness while observing live data/scan tool for intermittent changes

Typical sensor signal is a low-voltage signal within the module’s specified range (commonly 0–5 V).
A 'circuit high' condition generally means the sensor signal exceeds the maximum expected voltage (near or above the module’s high threshold, e.g., >4.5–5.0 V on 0–5 V systems).
If sensor is a thermistor, resistance will change with temperature (consult vehicle service data for resistance vs. temperature chart).
With the sensor disconnected, check for pull‑up voltage at the module connector (may read near reference/pull-up voltage).
A short to battery voltage will read near battery voltage on the signal pin (use caution to avoid damage).

Read and record freeze-frame and live data for the Brake Booster Temperature Sensor C using a scan tool. Confirm the C05B4 code and note when it set.
Perform a visual inspection of the brake booster area, sensor connector and harness for damage, corrosion, or water intrusion.
With ignition ON (engine off), backprobe the sensor signal pin and measure voltage. Compare to expected nominal range shown on scan tool.
Disconnect the sensor. Check for short to battery voltage at the harness connector (pin should not show battery voltage). Also check for short to ground.
If the sensor is a resistance-type thermistor, measure sensor resistance at ambient temperature and compare to service data. If out of spec, replace the sensor.
Perform a continuity check from the sensor connector to the control module input pin to verify no open circuit. Repair any open or high-resistance wiring.
If wiring and sensor check OK but signal still high, probe the module input pin for correct pull‑up and inspect module grounds. If module input is damaged, consider module testing/replacement per manufacturer procedures.
After repairs, clear codes and perform a functional test / short road test while monitoring live data. Confirm code does not return and sensor values are within expected range.
If intermittent, exercise harness and re-test; consider protecting/relocating wiring and installing dielectric grease on connectors as preventive measure.