P2E77

Code

Generic P — Powertrain

Hybrid/EV Battery Pack Coolant Temperature Sensor D Circuit High

Brand: Generic

Type: P — Powertrain

Views: UK: 43 EN: 55 RU: 57

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Page language: EN

Causes

Open circuit or very high resistance in the battery coolant temperature sensor circuit
Corroded or disconnected sensor connector or pins
Wiring short to battery positive or other high-voltage/ignition sources
Failed temperature sensor (thermistor)
Poor or missing ground at sensor or control module
Faulty battery management module (BMS) or PCM input

Symptoms

Battery pack coolant temperature readings erratic or showing abnormally low/high values in live data
Malfunction indicator lamp (MIL) or hybrid system warning illuminated
Battery thermal management system may run constantly or be disabled
Possible reduced hybrid/EV performance, charging restrictions, or limp mode
Noises from cooling system due to abnormal operation (fan/pump cycling)

What to check

Read stored and pending codes and freeze-frame data with a capable scan tool
Monitor live data for battery coolant temperature sensor voltage and reported temperature
Visually inspect sensor connector, pins, and harness for damage or corrosion
Backprobe connector and measure sensor signal voltage with ignition ON (do not start vehicle, follow HV isolation if required)
Measure sensor resistance at ambient temperature (with harness disconnected) and compare with manufacturer spec/thermistor chart
Check reference supply voltage and ground integrity at the sensor connector

Signal parameters

Signal voltage: typically within 0.1–4.9 V (varies by manufacturer) — code set when above upper threshold
Reference supply: usually a stable 5 V or 2.5 V reference from the BMS/ECU (verify spec)
Typical sensor type: NTC thermistor (resistance decreases as temperature increases); many sensors ≈10 kΩ at 25 °C (manufacturer-specific)
Normal operating coolant temperature range: roughly -40 °C to +125 °C (verify manufacturer limits)
Expected resistance vs temperature: use vehicle-specific thermistor chart for accurate values

Diagnostic algorithm

Retrieve DTC, freeze frame, and live data. Note when and under what conditions the code set.
Observe the battery pack coolant temperature sensor live voltage and reported temperature while the system is awake. Confirm voltage is above the upper threshold or fluctuating.
Visual inspection: shut vehicle down and follow HV safety procedures where applicable. Inspect sensor, connector, pins, and harness for corrosion, water intrusion, damage, or loose terminals.
With ignition ON (engine/motor OFF) and following safety precautions, backprobe the sensor connector. Measure signal voltage, reference voltage, and ground continuity. Compare to spec.
Disconnect the sensor and measure its resistance at ambient temperature. Compare to the manufacturer thermistor chart. If resistance is very high/open, the sensor is faulty.
Check wiring continuity between the sensor connector and the BMS/ECU. Check for shorts to battery voltage and shorts to ground.
If wiring and connector are good but signal still abnormal, substitute a known-good sensor (if available) or repair/replace the sensor.
After repairs, clear codes and perform an operational test. Monitor live data during a drive or system run to ensure the fault does not return.
If fault persists after sensor and wiring verification, consider module input fault and consult manufacturer diagnostic procedures for BMS/ECU testing or replacement.

Likely causes

Connector separation or corrosion at the sensor
Damaged wiring harness (chafing, broken conductor, water intrusion)
Sensor failure (internal open or degraded element)
High-resistance ground or poor pin contact
Intermittent harness short to supply voltage

Fault status

⚠️ Status

Stored when the battery pack coolant temperature sensor circuit voltage exceeds the expected upper threshold or the control module detects an open/high-resistance condition on the sensor input. Results in invalid or out-of-range battery coolant temperature readings and may trigger battery thermal management faults or reduced system performance.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours