P25C8

Code

Generic P — Powertrain

Brake Booster Temperature Sensor A Circuit Intermittent/Erratic

Brand: Generic

Type: P — Powertrain

Views: UK: 33 EN: 34 RU: 25

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Page language: EN

Causes

Loose, corroded, or contaminated connector at the sensor
Broken, frayed, or shorted wiring between sensor and control module
Poor ground or reference voltage to the sensor circuit
Failed or water-damaged brake booster temperature sensor
Intermittent internal module (PCM/ABS/BCM) fault or software anomaly
Moisture or debris intrusion into sensor or connector

Symptoms

Brake/ABS/traction control warning lamp illuminated intermittently or continuously
Erratic or rapidly fluctuating brake booster temperature value in live data
Reduced or altered behavior of systems that use brake booster temperature (may be limited on many vehicles)
DTC stored and may recur after driving or under certain temperature/humidity conditions
No other drivability symptoms in many cases (fault isolated to sensor circuit)

What to check

Read and record freeze frame and live data for brake booster temperature sensor
Perform a visual inspection of the sensor and connector for corrosion, damage, moisture, or deformation
Wiggle test harness and connector while watching live data to reproduce the intermittent signal
Check for proper reference voltage (typically 5 V) and a good ground at the sensor connector using a multimeter
Backprobe connector and measure sensor output voltage at cold and after warming to observe expected change
Perform continuity check of wiring between sensor connector and the control module, checking for intermittent shorts to ground or battery

Signal parameters

Typical sensor interface: 3-wire or 2-wire temperature sensor using reference voltage, signal, and ground (or 2-wire resistive to module)
Expected signal voltage range on most systems: ~0.5–4.5 V (varies by manufacturer) with lower/higher values representing cold/hot depending on sensor type
If NTC thermistor type: resistance decreases as temperature rises (verify expected resistance vs temperature from vehicle data)
Intermittent/erratic fault will show sudden spikes, drops, or rapid oscillation in the live sensor value
Update frequency: sensor value should change gradually with temperature; rapid jumps indicate electrical or sensor failure

Diagnostic algorithm

Retrieve freeze frame and live data; note conditions when fault occurred (ambient temp, runtime, cycling).
Visually inspect sensor, mounting, and connector; dry and clean connector if contaminated, then recheck.
Backprobe the sensor connector. With ignition on, verify reference voltage and ground. Record signal voltage at ambient temperature.
Warm or cool the booster area (heat gun or allow engine warm-up) while monitoring live data to confirm sensor responds smoothly to temperature change.
Wiggle the harness and connector while watching live data to reproduce intermittent behavior. If reproduced, repair/replace wiring or connector.
Perform continuity and insulation resistance checks on wiring to the module. Repair any open, short or high-resistance connections.
If wiring and connector are good, compare sensor resistance (if applicable) against manufacturer specification across temperature points; replace sensor if out of spec or unstable.
If sensor replacement does not clear intermittent and wiring and connector are confirmed good, consider module input circuit fault and consult manufacturer service information for module testing.
Clear codes and perform a road/drive cycle to verify repair; monitor for recurrence over several drive cycles and temperature conditions.

Likely causes

Corroded/loose pin(s) at sensor connector causing intermittent contact
Chafed wiring contacting chassis or other circuits causing intermittent short to ground/voltage
Sensor element beginning to fail and producing unstable resistance/voltage
Poor or intermittent ground at sensor or control module
Connector contaminated with moisture leading to temporary opens/shorts

Fault status

⚠️ Status

P25C8 — Brake Booster Temperature Sensor A Circuit Intermittent/Erratic. Intermittent or fluctuating sensor signal detected; inspect sensor, connector, and wiring.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours