A short to ground in the signal wire between sensor 6 and the PCM.; A faulty engine coolant temperature sensor 6 with an internal short.; Corroded, damaged, or loose electrical connectors at the sensor or PCM.; Wire chafing or pinching against engine components, causing a short to ground.; A malfunctioning PCM, though this is less common and should be diagnosed last.

DTC codes / P2Bxx · Hybrid propulsion / P2BB8

P2BB8Engine Coolant Temperature Sensor 6 Circuit Low

Q: What does code P2BB8 mean?

Engine Coolant Temperature Sensor 6 Circuit Low. P2BB8 indicates that the powertrain control module (PCM) has detected an abnormally low voltage signal on the circuit for engine coolant temperature sensor 6. This sensor is one of several temperature sensors used by the PCM to monitor coolant temperature, and a low signal typically means the circuit is shorted to ground or the sensor's internal resistance has dropped excessively.

P2BB8 indicates that the powertrain control module (PCM) has detected an abnormally low voltage signal on the circuit for engine coolant temperature sensor 6. This sensor is one of several temperature sensors used by the PCM to monitor coolant temperature, and a low signal typically means the circuit is shorted to ground or the sensor's internal resistance has dropped excessively.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaHybrid propulsion

Symptoms you may notice

Illumination of the check engine light (malfunction indicator lamp).
Often no symptoms besides the warning light, especially if the fault is intermittent.
Erratic or inaccurate temperature gauge readings on the dashboard.
Poor fuel economy or driveability issues if the PCM substitutes a default coolant temperature value.
Cooling fan may run continuously or not at all, depending on the PCM's failsafe strategy.
In rare cases, the engine may be hard to start or run rough when cold.

Common causes, most likely first

A short to ground in the signal wire between sensor 6 and the PCM.
A faulty engine coolant temperature sensor 6 with an internal short.
Corroded, damaged, or loose electrical connectors at the sensor or PCM.
Wire chafing or pinching against engine components, causing a short to ground.
A malfunctioning PCM, though this is less common and should be diagnosed last.

How to diagnose and fix it

Verify the code with a scan tool and check for any related pending or history codes.
Inspect the sensor 6 connector and wiring for obvious damage, corrosion, or loose pins.
Disconnect the sensor and measure resistance across its terminals; compare to the manufacturer's specification for the current temperature.
With the sensor disconnected, measure voltage on the signal wire at the sensor harness; a low voltage (near 0 V) indicates a short to ground in the wire.
Isolate the circuit by disconnecting the PCM and checking continuity to ground on the signal wire; repair any short found.
If the wiring and sensor test good, substitute a known-good sensor and clear the code to see if it returns.
As a last step, test the PCM for internal faults or reprogram it if required by the manufacturer's procedure.

What a low coolant sensor signal really means

A low signal voltage does not always mean the sensor itself has failed; a rubbed-through wire grounding against the engine block is a frequent culprit that many technicians overlook.
Some vehicles use multiple coolant temperature sensors for different functions, and sensor 6 may be part of a redundant monitoring system, so a failure may not immediately affect driveability.
The PCM may default to a fixed coolant temperature value when the signal is lost, which can mask symptoms and lead to misdiagnosis if the technician relies only on the temperature gauge.
After repairing the circuit, the code may not clear immediately because the PCM needs to see a valid signal through a complete warm-up cycle before it will turn off the light.
A faulty thermostat or low coolant level can cause temperature readings that mimic a sensor circuit fault, so always verify the cooling system's mechanical health before condemning the sensor.

Can I keep driving with P2BB8?

You can usually drive the vehicle with this code, but avoid extended idling or heavy loads until it is repaired, because the PCM may not control the cooling fan correctly and the engine could overheat. If the temperature gauge behaves erratically or the engine runs poorly, have it checked 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.