P0B25 – Hybrid/EV Battery Pack Temperature Sensor “C” Circuit Low

P0B25 is a diagnostic trouble code that points to a problem in the high-voltage battery temperature sensing circuit on a hybrid or electric vehicle. In simple terms, the control module is seeing an abnormal signal from one of the battery temperature sensors, which can affect how the pack is charged, cooled, and protected. You might notice warning lights, reduced power, or the engine running more often than normal. Because battery temperature is critical for safety and battery life, you should take this code seriously. This guide clearly explains the meaning, causes, diagnosis, and fixes for P0B25.

What Does P0B25 Mean?

P0B25 typically translates to “Hybrid/EV Battery Temperature Sensor ‘B’ Circuit Range/Performance” (wording can vary slightly by manufacturer). The hybrid/EV control module or powertrain control module (PCM) constantly monitors several temperature sensors inside or around the high-voltage battery pack. If the signal from sensor “B” is out of the expected range, jumps erratically, or does not match the other sensors, the module stores P0B25 and may illuminate the MIL or a hybrid system warning.

This code matters because the ECU uses battery temperature data to control cooling fans, pumps, charge rate, and power output. If it cannot trust that data, it will go into a protective strategy: reduced power, disabled EV mode, or even a no-start condition to prevent overheating or damage to the high-voltage battery.

Quick Reference

• OBD-II Family: P0B25
• Scope: Generic (Hybrid/EV specific, behavior can be manufacturer-dependent)
• System: High-Voltage Battery / Hybrid-Electric Powertrain
• Difficulty Level: Medium to High (high-voltage safety required)
• Estimated Repair Cost: €150 – €2,000+
• Last Updated: 2025-12-13

Real-World Example / Field Notes

In the shop, I’ve seen P0B25 a few times on Toyota and Lexus hybrids, as well as some GM plug-in models. One memorable case was a Prius that threw P0B25 along with a hybrid system warning and loud battery cooling fan operation. The owner had already priced a replacement battery pack, assuming it was “dead.”

After digging in, the actual fault was a corroded connector at one of the battery temperature sensor harness plugs. Moisture had wicked into the connector from the rear hatch area. The sensor itself tested fine with a multimeter, but the signal dropped out when we wiggled the harness. Cleaning the terminals, repairing a partially broken wire, and resealing the connector completely fixed the issue—no new battery needed. That’s why you always test the circuit instead of throwing big parts at a hybrid code.

Symptoms of P0B25

• Warning lights: Check Engine Light, hybrid system warning, or EV system malfunction indicator illuminated.
• Reduced performance: Noticeable loss of power, sluggish acceleration, or limited EV mode operation.
• Engine runs more: Gas engine staying on more than usual, even at low speeds or light loads.
• Cooling fan noise: High-voltage battery cooling fan running frequently or at high speed.
• Poor fuel economy: Decrease in MPG because the hybrid system is not using the battery efficiently.
• No-start or fail-safe: In severe cases, the vehicle may not go into “Ready” mode or may limit speed.
• Other hybrid codes: Additional battery or temperature-related DTCs stored alongside P0B25.

Common Causes of P0B25

Most Common Causes

• Faulty high-voltage battery temperature sensor “B” (open circuit, internal short, or drifted calibration).
• Damaged or corroded wiring/connectors in the battery temperature sensor harness.
• Poor terminal tension at the sensor connector causing intermittent signal loss.
• High-voltage battery pack hot spots causing readings outside normal range.
• Previous water intrusion in the rear battery compartment affecting the sensor circuit.

Less Common Causes

• Hybrid/EV battery ECU (battery management module) internal fault.
• Incorrectly installed replacement battery pack or sensor (pinched harness, misrouted wiring).
• Aftermarket modifications (audio systems, inverters) interfering with battery cooling or wiring.
• Connector damage from prior service, collision repairs, or rodent-chewed wiring.
• Software/calibration issue requiring an ECU update from the dealer.

Diagnosis: Step-by-Step Guide

Before replacing any parts, you need to verify whether P0B25 is caused by the sensor itself, the wiring, or the control module.

Tools You’ll Need: Quality scan tool with hybrid/EV data access, digital multimeter (DMM), basic hand tools, wiring diagram, back-probing pins, and ideally an infrared thermometer or thermal camera. For advanced checks, an oscilloscope and access to Mode $06 data are helpful. Always follow manufacturer high-voltage safety procedures and use insulated gloves when required.

1. Confirm the code and record freeze-frame data.
   Connect your scan tool, read all stored and pending DTCs, and note freeze-frame data for P0B25. Pay attention to battery temperature readings, state of charge, and vehicle speed when the code set. Clear the codes and see if P0B25 returns during a short drive.
2. Check live data for battery temperature sensors.
   In the hybrid/EV data list, view all battery temperature sensor values. Sensor “B” should read close to the others (usually within a few degrees C). If sensor B is stuck at a very low or high value, or jumps around while others are stable, you’ve found a strong suspect.
3. Visually inspect the battery area and harness.
   With the vehicle powered down and high-voltage system made safe per factory procedure, access the battery compartment. Look for signs of water intrusion, corrosion, damaged insulation, or loose connectors at the temperature sensors and battery ECU.
4. Check connector condition and pin fit.
   Disconnect the sensor B connector and inspect the terminals. Look for green corrosion, bent pins, or loose female terminals. Gently tug each wire to confirm it is fully crimped. Clean and repair as needed, then reconnect and retest live data.
5. Measure sensor resistance.
   With the sensor unplugged and the battery system safe, use your multimeter to measure resistance across the sensor terminals. Compare the reading to the service manual’s temperature/resistance chart. You can also warm or cool the sensor slightly (using a heat gun at a distance or a can of compressed air) and watch resistance change smoothly.
6. Check circuit continuity and reference voltage.
   With the key off, test continuity from the sensor connector back to the battery ECU connector for both signal and ground wires. Repair any open or shorted circuits. With key on (if safe to do so), check for proper 5 V reference and ground at the sensor connector as specified by the wiring diagram.
7. Compare sensor readings to actual temperature.
   Use an infrared thermometer or thermal camera to measure the surface temperature near the sensor’s location. Compare this to the scan tool’s reported temperature for sensor B. A large mismatch with a good circuit usually means the sensor is skewed or failing.
8. Check for related TSBs and software updates.
   Some manufacturers release Technical Service Bulletins for false P0B25 flags or revised thresholds. Check for TSBs and ECU calibration updates that may address nuisance codes or known harness issues.
9. Evaluate the battery ECU if everything else passes.
   If the sensor, wiring, and connectors all test good and readings are still erratic or implausible, the fault may be inside the battery ECU. Diagnosis at this level often requires factory scan tools or dealer-level support.

Pro Tip: On some vehicles, you can use Mode $06 or advanced data to see the exact test result and threshold that triggered P0B25. This helps you decide if the sensor is marginal, intermittent, or clearly failed. An oscilloscope on the signal wire can also reveal brief dropouts that a standard scan tool refresh rate might miss.

Possible Fixes & Repair Costs

• Replace high-voltage battery temperature sensor “B” – Installing a new OEM sensor when the original is out of spec or intermittent. Typical cost: €150 – €400 including labor.
• Repair or replace damaged sensor wiring/connector – Fixing corroded terminals, broken wires, or rodent damage in the harness. Typical cost: €120 – €350 depending on access.
• Clean and reseal battery compartment connectors – Removing corrosion, applying dielectric grease where specified, and resealing grommets to prevent future moisture entry. Typical cost: €100 – €250.
• Reposition or correctly install sensor after prior work – Correcting routing errors, pinched wiring, or improperly seated sensors after battery service. Typical cost: €80 – €200.
• Update hybrid/EV battery ECU software – Dealer flashing the latest calibration to address known false P0B25 triggers. Typical cost: €100 – €250.
• Replace hybrid/EV battery ECU (battery management module) – Only after confirming all sensors and wiring are good. Typical cost: €500 – €1,200+ including programming.
• Replace high-voltage battery pack – In rare cases of severe internal battery damage or multiple failing sensors integrated into the pack. Typical cost: €1,500 – €4,000+ depending on vehicle and pack type.

Always confirm the exact cause with proper testing before replacing expensive hybrid components.

Can I Still Drive With P0B25?

You can often drive short distances with P0B25, but it is not something to ignore. If the hybrid system is in reduced-power mode, the engine runs constantly, or you see a flashing warning light or feel shaking, you should stop driving and have the vehicle inspected. Continued driving with incorrect battery temperature control can shorten battery life or, in extreme cases, create a safety risk.

Last updated: January 22, 2026