P2B25

Code

Generic P — Powertrain

Hybrid/EV Electronics Coolant Temperature Sensor C Circuit Range/Perfomance

Brand: Generic

Type: P — Powertrain

Views: UK: 26 EN: 29 RU: 26

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Page language: EN

Causes

Faulty coolant temperature sensor (Sensor C)
Open or shorted wiring between sensor and hybrid control module/ECU
Poor or corroded connector/pin contact at sensor or control module
Low coolant level, air in cooling circuit, or blocked coolant flow around the sensor
Faulty ground or reference voltage at the control module
Intermittent connection from vibration or damaged harness

Symptoms

Malfunction Indicator Lamp (MIL) or fault light illuminated
Reduced hybrid/EV performance or system derate (limited regen/drive)
Electric coolant pump or thermal management operating abnormally
Battery charge/discharge management warnings or reduced charging
Cooling fan running continuously or failing to run as expected
Incorrect temperature readout or inability to reach normal operating temperature

What to check

Read freeze frame and live data with a scan tool: recorded sensor voltage/temperature and related temperatures
Visual inspection of sensor, connector, wiring and grounds for damage/corrosion
Check coolant level and inspect for air pockets or flow restrictions near sensor
Backprobe sensor connector and measure reference voltage and signal voltage with key ON (usually ~5 V reference, signal varies with temp)
Measure sensor resistance at ambient and while warming/cooling (compare to spec or look for smooth change)
Wiggle test harness while monitoring live data to find intermittent faults

Signal parameters

Sensor type: typically an NTC thermistor (resistance decreases as temperature rises)
Expected signal: analog voltage to controller — often in the range ~0.5–4.5 V depending on temperature
At cold ambient the sensor resistance is higher; at hot coolant resistance is lower (exact ohms vs °C vary by sensor)
Reference voltage commonly ~5 V; signal circuit must not be shorted to battery or ground
Signal should change smoothly with temperature; intermittent jumps indicate wiring or connector issues

Diagnostic algorithm

Retrieve code history, freeze frame, and live data. Note sensor C reading and other temperature sources (battery, inverter, ambient).
Visually inspect sensor and harness for damage, corrosion, coolant leaks, or loose connectors. Confirm coolant level and look for air pockets near sensor location.
With ignition ON (engine off), backprobe connector: verify reference voltage and ground at sensor connector, and measure sensor signal voltage. Compare to expected idle values.
Measure sensor resistance at engine cold and after warming the coolant (or apply heat using warm water) to confirm resistance changes smoothly. Compare to service spec if available.
Perform wiggle and continuity tests: monitor live data while flexing harness; check continuity and insulation resistance between sensor signal and ECU, and for shorts to battery and ground.
If wiring and connector are good but sensor readings are out of expected range, replace the sensor C and retest.
If a new sensor shows same fault and wiring checks good, consider control module input circuit testing or reprogramming per manufacturer procedures (this is less common and may require dealer-level tools).
Clear codes and perform a road/operation cycle or reproduction steps to verify the fault does not return. Confirm thermal management and hybrid functions restore normal behavior.

Likely causes

Sensor element failure (thermistor out of spec)
Damaged sensor harness (chafing, broken conductor, pinched wire)
Corroded terminal or water intrusion at sensor connector
Short to battery voltage or to ground in the sensor circuit
Insufficient coolant contacting the sensor or trapped air pocket
ECU/Hybrid control module fault (less common)

Fault status

⚠️ Status

DTC P2B25 stored. MIL may be illuminated. Hybrid/EV thermal management or charging/drive functions may be limited or derated while the fault is present. Readiness monitors related to coolant temperature may be affected until repair and verification are completed.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-2.5 hours