A faulty coolant temperature sensor on circuit C, such as an open thermistor element or internal damage.; Damaged, chafed, or corroded wiring in the sensor circuit C, including the signal or ground return path.; A loose or corroded electrical connector at the sensor or at the battery energy control module.; High resistance in a splice or terminal within the sensor circuit, often due to moisture intrusion.; A failed battery energy control module driver circuit for the sensor, though this is less common.; Aftermarket or incorrect sensor installation that does not match the OEM resistance curve.

DTC codes / P2Dxx · Hybrid propulsion / P2D55

P2D55Hybrid/EV Battery Pack Coolant Temperature Sensor C Circuit High

P2D55 indicates that the hybrid or electric vehicle battery pack coolant temperature sensor on circuit C is reporting a voltage above the normal range, which the battery energy control module interprets as an open circuit or excessive resistance. The computer sets this code when the sensor signal exceeds the calibrated high threshold for a set time, typically indicating a wiring fault, a failed sensor, or a poor connection rather than an actual overheating event.

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 electric-only driving range or a forced switch to gasoline engine operation in a plug-in hybrid.
A message on the dash indicating battery temperature is unavailable or that hybrid system performance is limited.
In rare cases, the vehicle may enter a fail-safe mode that restricts power output or prevents the high-voltage battery from charging.
Intermittent warning light activation when driving over bumps or in wet conditions, pointing to a wiring issue.

Common causes, most likely first

A faulty coolant temperature sensor on circuit C, such as an open thermistor element or internal damage.
Damaged, chafed, or corroded wiring in the sensor circuit C, including the signal or ground return path.
A loose or corroded electrical connector at the sensor or at the battery energy control module.
High resistance in a splice or terminal within the sensor circuit, often due to moisture intrusion.
A failed battery energy control module driver circuit for the sensor, though this is less common.
Aftermarket or incorrect sensor installation that does not match the OEM resistance curve.

How to diagnose and fix it

Verify the code with a scan tool and check for any related coolant temperature sensor codes to confirm the fault is isolated to circuit C.
Inspect the sensor connector and wiring harness for signs of damage, corrosion, or loose pins, and repair as needed.
Measure the resistance of the coolant temperature sensor with a multimeter and compare it to the manufacturer's specification for the ambient temperature.
Backprobe the sensor signal circuit at the control module connector and check for an open or high-resistance condition while wiggling the harness.
Check the sensor ground circuit for excessive voltage drop, repairing any high-resistance connections.
If the wiring and connections are good but the sensor resistance is out of range, replace the coolant temperature sensor.
Clear the code and perform a road test to confirm the repair, ensuring the sensor reading returns to a normal range.

Circuit C high is not always the sensor

A high voltage reading on a temperature sensor circuit almost always indicates an open circuit or a disconnected sensor, so inspect connectors and wiring before condemning the sensor itself.
The coolant temperature sensor for the hybrid battery pack is often a separate component from the engine coolant sensor, and technicians sometimes replace the wrong sensor.
On some vehicles, the sensor circuit C shares a ground with other sensors, so a fault in a common ground can set this code along with others.
Intermittent high readings can be caused by a harness that rubs against a metal bracket or passes near a heat source, leading to chafed insulation that only shorts when the vehicle is in motion.
A failed sensor may read a fixed high resistance when cold, mimicking an open circuit, so testing the sensor at multiple temperatures is more reliable than a single resistance check.

Can I keep driving with P2D55?

You can generally drive the vehicle with this code because it usually indicates a sensor circuit fault rather than an actual overheating condition, but avoid sustained high-speed or heavy-load driving until it is repaired. If the dash displays a battery temperature warning or the vehicle enters a reduced-power mode, stop driving and have it inspected promptly.

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.