An open circuit in the coolant temperature sensor signal wire, often due to a broken wire or corroded connector terminal; A failed coolant temperature sensor whose internal thermistor has drifted to a high-resistance state; A poor ground connection at the sensor or at the battery energy control module, causing a reference voltage offset; Coolant level that is too low, allowing the sensor to sit in air and read an incorrect high temperature; A short to voltage on the sensor signal circuit, which can mimic a high-resistance sensor; A faulty battery energy control module, though this is the least likely cause and should only be suspected after all circuit and sensor tests pass

DTC codes / P0Cxx · Hybrid propulsion / P0C45

P0C45Hybrid/EV Battery Pack Coolant Temperature Sensor A Circuit High

P0C45 indicates that the hybrid or electric vehicle battery pack coolant temperature sensor A circuit is reporting a voltage higher than the manufacturer's expected range. The battery energy control module sets this code when the sensor signal wire shows an abnormally high voltage, which usually means the circuit is open or the sensor's internal resistance has shifted out of specification.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaHybrid propulsion

Symptoms you may notice

Illumination of the check engine light or hybrid system warning light, often with no other noticeable symptoms
Reduced hybrid battery performance or a forced limp mode that limits electric-only operation
Battery cooling fan running continuously or not running at all, depending on the failure mode
A message on the dash indicating the hybrid battery is too hot or too cold, even when ambient temperatures are normal
Decreased fuel economy as the vehicle relies more heavily on the internal combustion engine
In rare cases, the vehicle may refuse to start or may shut down while driving if the battery management system cannot confirm safe coolant temperature

Common causes, most likely first

An open circuit in the coolant temperature sensor signal wire, often due to a broken wire or corroded connector terminal
A failed coolant temperature sensor whose internal thermistor has drifted to a high-resistance state
A poor ground connection at the sensor or at the battery energy control module, causing a reference voltage offset
Coolant level that is too low, allowing the sensor to sit in air and read an incorrect high temperature
A short to voltage on the sensor signal circuit, which can mimic a high-resistance sensor
A faulty battery energy control module, though this is the least likely cause and should only be suspected after all circuit and sensor tests pass

How to diagnose and fix it

Verify the coolant level in the hybrid battery pack reservoir and top it off with the specified coolant if it is low
Inspect the sensor connector and the wiring harness for chafing, corrosion, or loose pins, and repair any damage found
Measure the resistance of the coolant temperature sensor with a multimeter and compare it to the manufacturer's temperature-resistance chart
Back-probe the sensor signal circuit at the battery energy control module and check for an open circuit or excessive voltage drop
Check the sensor ground circuit for continuity to the battery energy control module ground point
If the circuit and sensor test good, substitute a known-good sensor and clear the code to see if it returns
Only after all other steps pass, follow the manufacturer's diagnostic flow for testing or replacing the battery energy control module

What a high-voltage sensor code really means

A high voltage reading on a temperature sensor circuit almost always indicates an open circuit or a sensor with excessive resistance, not a genuine overheating condition, so do not replace cooling system components before testing the wiring.
Low coolant level in the battery pack cooling loop is a commonly overlooked cause because the sensor can read air temperature instead of liquid temperature, producing a high-voltage signal that sets this code.
Corrosion inside the sensor connector is a frequent culprit on vehicles that live in humid climates or have been exposed to road splash, and it can create enough resistance to trigger the code without any visible wire damage.
This code can be set by a momentary glitch during battery pack service if the sensor connector is left unplugged and the ignition is turned on, so always clear codes and verify the fault is current before beginning diagnosis.
A short to voltage on the signal wire from a nearby harness can produce the same high-voltage reading as an open sensor, so a voltage drop test on the signal circuit is essential before condemning the sensor.

Can I keep driving with P0C45?

You can usually drive the vehicle short distances to a repair shop, but avoid long trips or heavy loads because the battery management system may limit power or disable electric-only mode. If the dash displays a high battery temperature warning or the vehicle enters limp mode, stop driving and have it towed to prevent damage to the hybrid battery pack.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.