Faulty coolant temperature sensor C itself, with internal intermittent open or short; Damaged or chafed wiring harness at the sensor connector or along the circuit; Corroded, loose, or water-intruded electrical connector at the sensor; Poor terminal tension or pin fit in the sensor or control module connector; Intermittent open or high resistance in the sensor ground circuit; Coolant level low or air pockets causing the sensor to read erratically; Failing hybrid battery control module or interface, though less common

DTC codes / P2Dxx · Hybrid propulsion / P2D56

P2D56Hybrid/EV Battery Pack Coolant Temperature Sensor C Circuit Intermittent/Erratic

P2D56 indicates that the hybrid or electric vehicle battery pack coolant temperature sensor C circuit is reporting an intermittent or erratic signal to the vehicle's control module. The computer has detected that the sensor's voltage or resistance readings are jumping unpredictably or dropping out, rather than producing a stable temperature value.

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
Intermittent reduction in hybrid system power or forced engine-only operation
Battery cooling fan running constantly or at unusual speeds
Dashboard message indicating battery temperature or cooling system fault
Reduced electric-only range or poor fuel economy
In rare cases, the vehicle may enter a limp mode or fail to start

Common causes, most likely first

Faulty coolant temperature sensor C itself, with internal intermittent open or short
Damaged or chafed wiring harness at the sensor connector or along the circuit
Corroded, loose, or water-intruded electrical connector at the sensor
Poor terminal tension or pin fit in the sensor or control module connector
Intermittent open or high resistance in the sensor ground circuit
Coolant level low or air pockets causing the sensor to read erratically
Failing hybrid battery control module or interface, though less common

How to diagnose and fix it

Verify coolant level and condition, and pressure-test the cooling system for leaks or air pockets
Inspect the sensor connector and wiring for corrosion, chafing, or loose pins, and repair as needed
Back-probe the sensor signal circuit and wiggle-test the harness while watching live data for erratic readings
Measure sensor resistance with a multimeter and compare to the manufacturer's temperature-resistance chart
Check the sensor ground circuit for excessive resistance or intermittent continuity
If wiring and connectors are good, replace the coolant temperature sensor C and clear the code
If the code persists, diagnose the hybrid battery control module and its connections

Intermittent sensor faults that fool technicians

A sensor that tests perfectly on a cold engine can still be intermittent when hot, so always wiggle-test the harness and monitor live data during a test drive.
Low coolant or trapped air is a frequent cause of erratic temperature readings that mimic a failed sensor, so always check the cooling system first.
The code can be set by a poor connection at the control module, not just at the sensor, so inspect both ends of the circuit.
Replacing the sensor without addressing a corroded connector often leads to a repeat failure within weeks.
Some vehicles use multiple coolant temperature sensors for the battery pack, and a fault in one can cause the others to read plausibly, masking the intermittent signal.

Can I keep driving with P2D56?

You can generally continue driving with this code, but avoid aggressive acceleration or long trips until it is repaired, because an erratic temperature signal can cause the hybrid system to reduce power or disable battery cooling. If the vehicle enters limp mode or shows a red battery temperature warning, stop safely and seek service.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

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