Faulty battery pack coolant temperature sensor A, such as an open or shorted internal element; Damaged or corroded wiring or connector at the sensor or along the harness; Coolant level low or air trapped in the battery cooling circuit causing inaccurate temperature readings; Failed coolant pump or restricted coolant flow leading to sensor readings outside the expected range; Powertrain control module software issue or internal fault in the sensor input circuit; Contamination or sludge on the sensor tip affecting its response time

DTC codes / P0Cxx · Hybrid propulsion / P0C42

P0C42Hybrid/EV Battery Pack Coolant Temperature Sensor A Circuit

Q: What does code P0C42 mean?

Hybrid/EV Battery Pack Coolant Temperature Sensor A Circuit. P0C42 indicates that the hybrid or electric vehicle battery pack coolant temperature sensor A circuit is reporting a voltage or signal outside the expected range, or the powertrain control module has detected an implausible reading from that sensor. The computer monitors this circuit to ensure the high-voltage battery stays within a safe operating temperature, and it sets the code when the signal does not match the model's expected values.

P0C42 indicates that the hybrid or electric vehicle battery pack coolant temperature sensor A circuit is reporting a voltage or signal outside the expected range, or the powertrain control module has detected an implausible reading from that sensor. The computer monitors this circuit to ensure the high-voltage battery stays within a safe operating temperature, and it sets the code when the signal does not match the model's expected values.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaHybrid propulsion

Symptoms you may notice

Illumination of the check engine light or a dedicated hybrid system warning light
Often no symptoms besides the warning light, especially if the fault is intermittent
Reduced electric-only driving range or forced engine operation in a plug-in hybrid
A message on the dash indicating the hybrid battery is too hot or too cold
Possible reduced power output or a limp-home mode in severe cases
Cooling fan for the battery pack running continuously or not at all

Common causes, most likely first

Faulty battery pack coolant temperature sensor A, such as an open or shorted internal element
Damaged or corroded wiring or connector at the sensor or along the harness
Coolant level low or air trapped in the battery cooling circuit causing inaccurate temperature readings
Failed coolant pump or restricted coolant flow leading to sensor readings outside the expected range
Powertrain control module software issue or internal fault in the sensor input circuit
Contamination or sludge on the sensor tip affecting its response time

How to diagnose and fix it

Verify the coolant level in the hybrid battery cooling system and top up with the specified coolant if low
Inspect the sensor connector and harness for corrosion, chafing, or loose pins, and repair as needed
Measure the resistance of the coolant temperature sensor with a multimeter and compare to the manufacturer's temperature-resistance chart
Back-probe the sensor signal wire at the control module and check for a voltage that tracks temperature changes
Check for continuity and short-to-ground or short-to-power on the sensor circuit wiring
If the sensor is out of specification, replace it and clear the code, then verify the reading with a scan tool
If the circuit and sensor test good, check for technical service bulletins or software updates for the control module before condemning it

What the coolant sensor code really means

A low coolant level or air pocket in the battery cooling loop can set this code without any sensor fault, so always check the coolant level and bleed the system first.
The sensor may test fine at room temperature but fail when hot or cold, so a resistance check across a temperature range is more reliable than a single reading.
In some vehicles, a failing coolant pump or a blocked cooling passage causes the sensor to read a temperature that is plausible but outside the expected range, triggering the code.
The code can be set by a momentary glitch in the circuit, so an intermittent fault may not reappear during a short test drive and may require monitoring live data over time.
Do not replace the sensor based solely on the code; a thorough circuit test often reveals a wiring issue that a new sensor will not fix.

Can I keep driving with P0C42?

You can usually continue driving with this code if the vehicle is not overheating and no power reduction is present, but avoid heavy acceleration or long grades that stress the battery. If the hybrid system warning light is on or the vehicle enters limp mode, stop driving and have it inspected promptly to prevent battery damage.

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.