P2E71

Code

Generic P — Powertrain

Hybrid/EV Battery Pack B Cell Thickness Sensor Circuit High

Brand: Generic

Type: P — Powertrain

Views: UK: 29 EN: 33 RU: 32

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Page language: EN

Causes

Sensor shorted to battery positive or other high-voltage source
Damaged wiring harness or pin pushed out at connector
Corroded/contaminated connector or poor terminal contact
Faulty cell thickness (swelling) sensor
Battery management module (BMS) internal fault or incorrect reference
Water/contaminant intrusion into sensor area or connector

Symptoms

Hybrid/EV fault indicator / MIL illuminated
Possible reduced charging or power availability (BMS may derate or disable charging)
Possible limp-home mode or reduced drive performance if BMS limits power
Charging may be inhibited or stop
Fault stored in vehicle data; related battery pack warnings or error messages

What to check

Read and record freeze frame and live data from BMS and related modules
Check for any other battery-pack DTCs (Pack A/B, cell imbalance, temperature sensors)
Perform a visual inspection of Pack B sensor wiring, connectors and harness for damage, chafing, corrosion, or moisture
Inspect the sensor mounting and surrounding cells for signs of swelling or physical damage
With appropriate high-voltage safety procedures, access the sensor connector and backprobe the signal, reference and ground pins to measure voltages
Check continuity and resistance between sensor and BMS connector (key off) to identify opens or shorts

Signal parameters

Typical sensor output: analog 0–5.0 V (manufacturer-dependent)
“Circuit High” threshold commonly >4.5 V (vehicle-specific)
Reference/ground should be stable (near 0 V) with ignition on
When sensor disconnected, control module input often reads open/high or a defined fail-safe value (check manufacturer service data)

Diagnostic algorithm

Retrieve freeze-frame data and any related battery codes; note pack voltage, pack temperature and live sensor value for Pack B.
Visually inspect Pack B sensor, connector, and wiring for damage, corrosion, or signs of water ingress. Repair obvious issues and retest.
With high-voltage system disabled and following safety procedures, disconnect Pack B sensor connector. Inspect pins for damage or corrosion.
With vehicle in IG-ON (follow HV safety), backprobe the sensor connector: measure signal voltage, reference and ground. Compare to expected ranges. A stable high voltage (>4.5 V) at the module side suggests a short to a high source or module fault.
Measure continuity between the sensor signal pin and the BMS input pin (ignition off). Check for short to pack positive, accessory power, or short to ground. Repair wiring as required.
If wiring checks good, reconnect sensor and measure sensor output directly (if safe) or substitute a known-good sensor if available. If a replacement sensor cures the fault, replace sensor.
If a new sensor and repaired wiring do not clear the code, suspect BMS input circuit or internal module fault. Consult manufacturer service information for module testing/repair or replacement procedures.
After repairs, clear the DTC, perform a full BMS self-test or relearn procedure if required, and verify the fault does not return during normal charge/discharge cycles.

Likely causes

Failed or shorted cell thickness sensor on Pack B
Open/shorted harness between sensor and BMS (short to pack or accessory voltage)
Corroded connector at sensor or BMS
BMS input circuit failure

Fault status

⚠️ Status

Hybrid/EV Battery Pack B Cell Thickness Sensor Circuit High — sensor signal above expected range. BMS may derate or disable charging/drive for safety until condition is resolved.

🔴 Repair difficulty: Hard

⏱️ Diagnostic time: 2.0-4.0 hours