A broken, chafed, or disconnected signal wire between sensor C and the control module; Corroded or loose terminals at the sensor connector or at the control module harness; An open circuit inside the coolant temperature sensor itself; A poor ground connection for the sensor circuit, causing a reference shift; A faulty control module driver circuit, though this is rare; Coolant contamination or a sensor installed with the wrong thread sealant that affects the ground path

DTC codes / P2Bxx · Hybrid propulsion / P2B27

P2B27Hybrid/EV Electronics Coolant Temperature Sensor C Circuit High

P2B27 means the hybrid or electric vehicle's electronics coolant temperature sensor C is reporting a voltage above the normal range, so the computer sees an open circuit or a signal that is too high. The powertrain control module uses this sensor to monitor the coolant that cools the inverter, DC-DC converter, and other high-voltage electronics, and it sets this code when the signal wire reads near reference voltage instead of a valid temperature signal.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaHybrid propulsion

Symptoms you may notice

Illumination of the check engine light or a hybrid system warning message on the dash
Often no symptoms besides the warning light, especially if the fault is intermittent
Reduced power or a limp-home mode if the computer derates the hybrid system to protect the electronics
Possible overheating warning for the hybrid electronics, though this is less common with a high-signal fault
In some vehicles, the engine may run continuously or the hybrid system may refuse to enter electric-only mode

Common causes, most likely first

A broken, chafed, or disconnected signal wire between sensor C and the control module
Corroded or loose terminals at the sensor connector or at the control module harness
An open circuit inside the coolant temperature sensor itself
A poor ground connection for the sensor circuit, causing a reference shift
A faulty control module driver circuit, though this is rare
Coolant contamination or a sensor installed with the wrong thread sealant that affects the ground path

How to diagnose and fix it

Scan all modules for stored and pending codes, and record freeze-frame data to see when the fault occurred
Inspect the sensor connector and harness for damage, corrosion, or loose pins, and repair as needed
Measure the sensor resistance with a multimeter and compare it to the manufacturer's temperature-resistance chart
Back-probe the signal wire at the control module and check for an open circuit or excessive voltage drop
Check the sensor ground circuit for continuity and resistance to the control module ground
If the wiring and ground are good, replace the coolant temperature sensor C and clear the codes
After repair, clear codes and verify the sensor reading matches actual coolant temperature during a road test

What a high signal really tells you

A high signal voltage almost always means an open circuit, not a hot condition, so do not replace the sensor before checking the wiring and grounds.
The sensor C circuit often shares a ground or reference with other sensors, so a fault in a neighbouring circuit can set this code and mislead you.
Intermittent codes that appear only on cold mornings or rough roads frequently trace to a chafed harness near a sharp bracket or a connector that is not fully latched.
Some vehicles will set this code and still drive normally because the control module substitutes a default coolant temperature, hiding the fault from the driver.
Clearing the code without repairing the root cause will usually result in the code returning after a few drive cycles, so always verify the live data after a repair.

Can I keep driving with P2B27?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy loads, long trips, or aggressive driving because the hybrid electronics may overheat without a valid temperature signal. If the dash shows a red hybrid system warning or reduced power, stop safely and have the vehicle towed.

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.