P0C31 – Drive Motor “B” Inverter Temperature Sensor Circuit Low

P0C31 is a hybrid/EV trouble code that points to a problem in the high-voltage battery pack’s temperature monitoring circuit. In plain terms, your car’s computer is seeing something wrong with how one of the battery temperature sensors is reading or how its circuit is behaving. This can affect hybrid performance, battery life, and sometimes drivability. On many Toyota, Lexus, GM, Ford, and other hybrids, this code needs attention sooner rather than later, but it doesn’t always mean the entire battery pack is bad.

What Does P0C31 Mean?

P0C31 is a generic OBD-II diagnostic trouble code that typically translates to “Hybrid Battery Temperature Sensor ‘A’ Circuit Range/Performance” or a very similar description, depending on the manufacturer. It indicates the powertrain control module (PCM) or hybrid control ECU has detected a temperature signal from one of the battery sensors that’s out of the expected range or not behaving as it should.

The high-voltage battery pack uses multiple temperature sensors to protect the cells from overheating or operating when too cold. If the ECU sees a voltage that doesn’t match real-world conditions, it sets P0C31 and may limit hybrid operation to protect the battery and power electronics.

Quick Reference

• Code: P0C31
• Type: Hybrid/EV high-voltage battery temperature sensor circuit fault
• Severity: Moderate to high (battery and drivability concerns)
• Common Fixes: Repair wiring, replace temperature sensor, service or replace battery pack
• Driveability: Often driveable, but hybrid performance may be reduced

Real-World Example / Field Notes

In the shop, I most often see P0C31 on higher-mileage hybrids that have started to lose battery efficiency. A typical case: a Toyota hybrid comes in with the check engine light and hybrid system warning on, plus reduced fuel economy. Scan data shows one battery temperature sensor stuck at an impossible value, like -40°F or 250°F, while the others look normal. After checking wiring and connectors near the battery cooling fan, corrosion is found in the sensor connector. Cleaning and repairing the connector, then clearing the code, restores normal readings and hybrid performance.

Symptoms of P0C31

• Check engine light illuminated, often with a hybrid system or master warning light
• Reduced hybrid assist or the engine running more often than usual
• Poor fuel economy compared to your normal average
• Battery cooling fan running more frequently or at higher speed than normal
• Limited EV mode or EV mode not engaging at all
• Rough transitions between electric motor and gasoline engine
• Fail-safe / limp mode in some cases, with reduced power
• Additional hybrid battery codes stored alongside P0C31

Common Causes of P0C31

Most Common Causes

• Faulty battery temperature sensor: The sensor inside or attached to the high-voltage battery pack can fail internally, sending incorrect voltage to the ECU.
• Damaged wiring or connectors: Corrosion, moisture intrusion, rodent damage, or vibration can break or short the sensor wiring harness.
• Aging high-voltage battery pack: As cells degrade, they can run hotter and trigger abnormal readings or stress the sensor circuit.
• Battery cooling system issues: A clogged battery cooling fan or blocked air ducts can cause real overheating, which the ECU interprets as a sensor/circuit problem.
• Previous battery work: Improperly reconnected sensors or pinched harnesses after battery replacement or service.

Less Common Causes

• Hybrid control ECU fault: Internal failure in the ECU’s temperature monitoring circuit (rare but possible).
• Poor ground or power supply: Voltage drops or unstable reference voltage affecting sensor readings.
• Water intrusion in battery compartment: Moisture causing intermittent shorts or high resistance in connectors.
• Aftermarket modifications: Non-factory wiring, added fans, or poorly installed accessories near the battery pack.

Diagnosis: Step-by-Step Guide

To diagnose P0C31 properly, you need at least a good scan tool that can read hybrid system data, a digital multimeter, and basic hand tools. For in-depth work on the high-voltage battery, insulated gloves and proper safety equipment are mandatory. If you’re not comfortable around high-voltage systems, have a qualified hybrid technician handle the deeper steps.

1. Confirm the code and record data: Use a scan tool to confirm P0C31 is present. Record freeze-frame data and look for any related hybrid battery or cooling fan codes.
2. Check live data for battery temperatures: In the hybrid battery data list, compare all temperature sensor readings. Look for one sensor that’s way off (stuck low, stuck high, or jumping around).
3. Inspect the battery cooling system: Verify the cooling fan operates, intake vents are clear, and no debris is blocking airflow to the battery pack.
4. Visual inspection of wiring and connectors: With the vehicle powered down and safe, inspect accessible connectors and harnesses to the battery pack and temperature sensors. Look for corrosion, green crust, broken insulation, or loose pins.
5. Check sensor circuit with a multimeter: Following the service manual, back-probe the suspect sensor circuit. Verify reference voltage, ground integrity, and sensor signal voltage. Compare to factory specs.
6. Wiggle test the harness: While monitoring live data or voltage, gently move the wiring harness and connectors. If readings change or the sensor drops out, you’ve likely found an intermittent wiring fault.
7. Use Mode $06 or enhanced data: Some scan tools allow you to view test results for individual sensors. Check for borderline values or tests that are close to failing.
8. Substitute or test the sensor (if serviceable): On some models, you can unplug the suspected sensor and measure its resistance at known temperatures or temporarily swap sensors (if identical) to see if the fault follows the sensor.
9. Check for TSBs and software updates: Look up technical service bulletins for your vehicle. Some manufacturers release updated calibration or known fixes for recurring P0C31 issues.
10. Evaluate battery health: If sensor and wiring check out, perform a full hybrid battery health check. Uneven cell temperatures or voltages may indicate a failing pack that’s triggering the code.

Pro Tip: Always disconnect the high-voltage service plug and follow the manufacturer’s wait time before opening or working near the battery pack. The orange cables and components can carry lethal voltage even with the 12V battery disconnected.

Possible Fixes & Repair Costs

The exact repair for P0C31 depends on what you or your technician find during diagnosis. In many cases, the fix is relatively straightforward, such as repairing corroded wiring or replacing a single temperature sensor. In more severe cases, the high-voltage battery pack may need reconditioning or replacement.

• Repair or replace wiring/connectors: Cleaning corrosion, repairing broken wires, or replacing a connector can cost around $100–$350 depending on access and labor time.
• Replace battery temperature sensor: If the sensor is serviceable separately, expect roughly $150–$450 parts and labor, depending on vehicle and access.
• Battery cooling fan or duct repair: Cleaning or replacing a faulty fan or blocked ducting typically runs $150–$500.
• Hybrid battery reconditioning or module repair: Some shops offer reconditioning or module replacement in the $600–$1,500 range.
• Full hybrid battery replacement: A new or remanufactured pack can range from $2,000 to $5,000+ installed, depending on brand, model, and warranty.

Typical repair costs for P0C31 are heavily influenced by vehicle make, mileage, whether the battery is still under warranty, and how deep the fault goes (simple wiring vs. major battery failure).

Can I Still Drive With P0C31?

In most cases, you can still drive with P0C31 for a short time, but it’s not something you should ignore. The hybrid system may limit power, disable EV mode, or run the engine more often to protect the battery. You might notice reduced performance and worse fuel economy. If additional warning lights appear, the vehicle goes into limp mode, or you notice overheating smells or unusual fan noise, you should stop driving and have it checked immediately. When in doubt, treat hybrid battery codes as higher priority.

What Happens If You Ignore P0C31?

If you ignore P0C31, you risk running the high-voltage battery pack at unsafe temperatures or with poor monitoring. Over time, this can accelerate battery degradation, lead to expensive battery replacement, and in extreme cases cause overheating that may damage nearby components. The car may also become less reliable, with sudden loss of hybrid assist or limp mode at inconvenient times.

Last updated: January 22, 2026

Vehicles Commonly Affected by P0C31

P0C31 shows up most often on hybrid and plug-in hybrid models from major manufacturers. You’ll commonly see it on Toyota Prius, Camry Hybrid, Highlander Hybrid, and similar Lexus hybrids, as well as Ford Escape/ Fusion hybrids, GM hybrids (Chevrolet, GMC, Cadillac), and some Honda and Hyundai/Kia hybrid models. Any vehicle that uses a multi-sensor high-voltage battery pack and active cooling system can potentially set this code as the pack ages or if the cooling system is neglected.