P0E37 – Hybrid/EV Battery Coolant Control Valve Circuit Low

P0E37 is a hybrid/EV trouble code that points to a problem in the high-voltage battery pack’s temperature sensing system, specifically an out-of-range or performance issue on one of the temperature sensor circuits. When this code sets, your hybrid or electric vehicle’s ECU may limit power, disable EV mode, or run the cooling fans more often to protect the battery. You might notice reduced fuel economy, warning lights, or the engine running more than usual. This guide walks you through what P0E37 means, symptoms, causes, diagnosis steps, and typical repair options.

What Does P0E37 Mean?

P0E37 is a generic hybrid/EV diagnostic trouble code that usually translates to something like “Hybrid/EV Battery Pack Temperature Sensor ‘B’ Circuit Range/Performance.” The exact wording can vary by manufacturer, but the idea is the same: the ECU is seeing a temperature reading from one section of the high-voltage battery pack that doesn’t make sense compared to expected values.

This can be due to a failing temperature sensor, wiring issues in the sensor circuit, or an internal problem in the battery pack or battery energy control module. The ECU sets P0E37 when the sensor signal is stuck, jumps around, or disagrees too much with other pack temperature sensors.

Quick Reference

  • Code: P0E37
  • System: Hybrid/EV high-voltage battery temperature monitoring
  • Typical meaning: Battery pack temperature sensor “B” circuit range/performance
  • Severity: Moderate to high (possible battery protection mode)
  • Common fix: Repair wiring or replace faulty battery temperature sensor/module

Real-World Example / Field Notes

In the shop, you often see P0E37 on older hybrids that have spent years in hot climates or stop-and-go traffic. A common scenario: the customer complains that the hybrid battery fan runs constantly, fuel economy dropped, and the check engine or hybrid system warning light came on. Scanning the ECU shows P0E37 plus maybe a couple of related temperature codes. After pulling live data, one battery temperature sensor will read something crazy like -40°F or 250°F while the others look normal. In many cases, the fix ends up being a corroded connector or a failed thermistor sensor inside the battery pack.

Symptoms of P0E37

  • Warning lights: Check Engine Light, hybrid system warning, or EV system malfunction indicator illuminated.
  • Reduced performance: The vehicle may limit power, feel sluggish, or restrict EV-only operation.
  • Increased engine use: The gasoline engine may run more often to protect or cool the high-voltage battery.
  • Cooling fan noise: High-voltage battery cooling fan running more frequently or at higher speed than normal.
  • Poor fuel economy: Reduced MPG due to loss of efficient hybrid operation.
  • Charging issues: On plug-in hybrids or EVs, charging may slow down, stop early, or be disabled.
  • Limited range: Shorter EV range or reduced state-of-charge window available.
  • No-start in severe cases: Some vehicles may refuse to go into READY mode if the ECU thinks the battery is at a dangerous temperature.

Common Causes of P0E37

Most Common Causes

  • Faulty battery temperature sensor: The thermistor or sensor module for the affected “B” channel fails and sends incorrect voltage to the ECU.
  • Corroded or loose connector: Moisture, dirt, or vibration damages the connector at the sensor or battery control module, causing intermittent or high-resistance connections.
  • Damaged wiring harness: Chafed, pinched, or broken wires in the high-voltage battery temperature sensor circuit, often near the pack or under rear seats.
  • Internal battery pack issues: Localized overheating or a failing module can skew temperature readings and trigger a range/performance fault.
  • Battery energy control module fault: The module that reads the temperature sensors misinterprets the signal or has an internal failure.

Less Common Causes

  • Previous collision or water intrusion: Rear-end impacts or flooding can damage the battery pack, wiring, or sensors.
  • Poor aftermarket repairs or modifications: Incorrectly routed wiring, missing clips, or non-OEM sensors installed during previous work.
  • Software/firmware issues: Rarely, an ECU calibration bug may mis-handle certain sensor readings until updated.
  • Extreme operating conditions: Prolonged high-load driving in hot weather with a dirty or blocked battery cooling intake can stress sensors and wiring.

Diagnosis: Step-by-Step Guide

To diagnose P0E37 correctly, you should have a quality scan tool that can read hybrid/EV data, a digital multimeter, and access to factory wiring diagrams or service information. If you are not comfortable working near high-voltage components, let a qualified hybrid technician handle the internal battery pack checks.

  1. Confirm the code and record data: Scan the vehicle for DTCs. Note P0E37 and any related battery or temperature codes. Save freeze-frame data to see what temperature and voltage values the ECU saw when the code set.
  2. Check live battery temperature data: With the scan tool, compare all high-voltage battery temperature sensor readings. Look for one sensor that is clearly out of line (for example, much hotter, much colder, or stuck at a fixed value).
  3. Inspect battery cooling system: Check the battery cooling fan, ducts, and intake grilles (often near the rear seat or cargo area). Make sure nothing is blocked by debris, pet hair, or luggage.
  4. Perform a visual inspection of wiring: With the 12V system off and following safety procedures, visually inspect the harness and connectors going to the battery pack temperature sensors and battery control module. Look for corrosion, broken locks, or damaged insulation.
  5. Check connectors for corrosion or spread terminals: Disconnect the suspect sensor connector (if accessible) and inspect the pins. Green corrosion, moisture, or loose terminals can easily cause a range/performance fault.
  6. Measure sensor circuit resistance/voltage: Using the wiring diagram, back-probe or bench-test the temperature sensor. Most use a thermistor that changes resistance with temperature. Compare your readings to the service manual specs at room temperature.
  7. Wiggle test the harness: While watching live data on the scan tool, gently move the harness and connectors. If the temperature reading jumps or drops out, you’ve likely found a wiring or connector issue.
  8. Check Mode $06 data (if available): Some scan tools allow you to view Mode $06 test results for the battery temperature monitor. This can show which specific monitor failed and how close readings are to limits.
  9. Verify battery control module operation: If the sensor and wiring test good but the reading is still wrong, follow factory tests for the battery ECU. This may include pin-out checks, power/ground verification, and sometimes substitution with a known-good sensor.
  10. Clear codes and road test: After repairs, clear P0E37 and perform a road test while monitoring battery temperatures. Confirm that readings remain stable and the code does not return.

Pro tip: Always follow the manufacturer’s high-voltage disable procedure before opening or removing any battery covers. Even temperature sensors sit very close to high-voltage components, and safety comes first.

Possible Fixes & Repair Costs

The exact repair for P0E37 depends on what you find during diagnosis. Common fixes include cleaning or repairing corroded connectors, replacing a faulty battery temperature sensor, repairing damaged wiring, or in more serious cases, replacing a section of the high-voltage battery pack or the battery energy control module. Typical repair costs can range from about $150–$350 for wiring or connector repairs, $300–$800 for sensor or module replacement, and $1,000–$3,000+ if a significant portion of the battery pack is replaced. Labor rates, parts availability, and whether you use OEM or remanufactured components all affect the final price.

Can I Still Drive With P0E37?

In many cases, you can still drive with P0E37, but the vehicle may go into a limited-operation or “limp” mode. The ECU will prioritize battery protection, so you might notice reduced power, more engine operation, or disabled EV mode. Short, gentle trips are usually safe if the car still goes into READY and drives normally, but you should avoid heavy loads, steep hills, and high ambient temperatures until it’s checked. If you see additional warnings like “Stop Safely Now” or the vehicle refuses to go into READY, do not continue driving—have it towed to a shop.

What Happens If You Ignore P0E37?

If you ignore P0E37, you risk overheating or unevenly stressing parts of the high-voltage battery pack. Over time this can accelerate battery degradation, trigger more severe hybrid system faults, and eventually leave you with a no-start or very expensive battery replacement. It’s much cheaper to fix a sensor or wiring issue early than to wait until the pack is damaged.

Need wiring diagrams and factory-style repair steps?

Powertrain faults often require exact wiring diagrams, connector pinouts, and guided test steps. A repair manual can help you confirm the cause before replacing parts.

Factory repair manual access for P0E37

Check repair manual access

Compare nearby valve hybrid/ev trouble codes with similar definitions, fault patterns, and diagnostic paths.

  • P0E19 – Hybrid/EV Battery Pack Coolant Flow Sensor Circuit Low
  • P0E14 – Hybrid/EV Battery Pack Coolant Pump Control Circuit Low
  • P0E2D – Hybrid/EV Battery Heater “D” Control Circuit Low
  • P0E28 – Hybrid/EV Battery Heater “C” Control Circuit Low
  • P0E23 – Hybrid/EV Battery Heater “B” Control Circuit Low
  • P0E1E – Hybrid/EV Battery Heater “A” Control Circuit Low

Key Takeaways

  • P0E37 points to an abnormal reading from one of the high-voltage battery temperature sensors.
  • Common causes include a bad sensor, wiring or connector problems, or an issue inside the battery pack.
  • Symptoms range from warning lights and reduced power to constant fan operation and poor fuel economy.
  • Diagnosis requires a capable scan tool, wiring diagrams, and strict high-voltage safety procedures.
  • Repairs can be relatively minor or quite expensive, so catching the problem early is important.

Vehicles Commonly Affected by P0E37

You’ll most often see P0E37 on hybrids and EVs from manufacturers like Toyota and Lexus (Prius, Camry Hybrid, RX Hybrid), Honda and Acura (Accord Hybrid, Insight, MDX Hybrid), Ford and Lincoln (Fusion Hybrid, C-Max, MKZ Hybrid), GM brands (Chevrolet Volt, Malibu Hybrid), and some Hyundai/Kia hybrid and plug-in models. Any vehicle using a multi-sensor high-voltage battery pack can set this code, especially as mileage climbs or if the car operates in hot, dusty environments.

FAQ

Can I clear P0E37 myself with a scan tool?

You can clear P0E37 with a basic OBD2 scanner, but if the underlying issue is still present, the code will usually return quickly. Use the scan tool to read live battery temperature data and guide your diagnosis instead of just erasing the code.

Is P0E37 dangerous to drive with?

P0E37 doesn’t usually mean the car will instantly fail, but it does indicate the ECU is worried about battery temperature accuracy. If the vehicle drives normally and only shows a warning light, you can typically drive short distances to a shop. If it shows severe warnings, shuts down, or feels unsafe, stop driving and get it towed.

How is a faulty battery temperature sensor replaced?

On most hybrids and EVs, the temperature sensors are mounted inside or on the surface of the high-voltage battery pack. Replacing one often requires disabling the high-voltage system, removing interior trim, lifting the battery pack cover, and swapping the sensor or sensor harness. This is not a DIY job unless you are trained and have the right safety gear.

Can bad battery cooling cause P0E37?

Yes. If the battery cooling fan is weak, the intake is blocked, or ducts are disconnected, certain areas of the pack can run hotter than others. That temperature imbalance can trigger range/performance codes like P0E37, as the ECU sees one sensor much hotter than the rest.

How do I know if the problem is wiring or the sensor itself?

You need to compare live data with physical tests. If a sensor reads wildly off, check its connector and harness for damage. Measure resistance at the sensor and at the control module side. If resistance is correct at the sensor but not at the module, the wiring is suspect. If resistance is out of spec at the sensor itself, the sensor is likely bad.