P2BB9: Engine Coolant Temperature Sensor 6 Circuit High

The ECM detects a circuit high fault on the engine coolant temperature sensor 6. Reading cannot be used reliably for control.

Medium severity. Can I keep driving?Watch the temperature gauge. If it climbs or a warning appears, stop the car in a safe place and turn off the engine: overheating can cause serious damage.

Symptoms

Check engine light on
Cooling fan runs constantly or not at all
Cabin heater weak or excessively hot
Possible long warm-up time or hard cold start

Most likely causes

Signal wire shorted to B+
Open sensor
Connector pins corroded - high contact resistance

What to check, in order

Start with the simplest. You can tick off each step.

With the engine cold, check the coolant level; never do this when the system is hot
Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
Check the actual temperature in live data
Make sure the fan comes on when it should
Check the thermostat and connector
Measure the sensor and replace it if its readings do not make sense

Good to know

Repair difficulty: easy
It affects emissions.

What each character of P2BB9 means

P: Powertrain: engine and transmission
2: Generic code: same on every make
B: Subsystem depends on the code range
B9: Specific fault in that system

Frequently asked questions

Can I keep driving with code P2BB9?

Watch the temperature gauge. If it climbs or a warning appears, stop the car in a safe place and turn off the engine: overheating can cause serious damage.

What causes code P2BB9?

The most common causes are: signal wire shorted to B+; open sensor; connector pins corroded - high contact resistance.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.