Damaged, corroded or loose wiring or connector at the radiator coolant temperature sensor; Faulty radiator coolant temperature sensor (reading drifted or failed); Low coolant level or air in the cooling system giving a false or unstable reading; Thermostat stuck open or closed, so the reading does not match the engine temperature; Short or open circuit in the sensor signal or reference wiring, or a poor earth; Fault in the control unit or its sensor reference supply.

P00B1

Radiator Coolant Temperature Sensor Circuit.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
0: AreaFuel and air metering, auxiliary emission controls
B1: FaultThe specific fault in that area

What it means

P00B1 is a generic code for a fault in the radiator coolant temperature sensor circuit. This sensor measures coolant temperature at the radiator, usually the outlet side, and is separate from the engine coolant temperature sensor. The control unit set the code because the sensor signal was implausible, for example out of its normal range or not matching the other temperature readings. The exact test conditions vary by manufacturer and engine.

Symptoms

Engine warning light on
Temperature gauge reading oddly or behaving erratically
Cooling fans running constantly or not coming on when expected
Poor fuel economy or slightly rough running if the control unit uses a default temperature
Hard or long starting in some cases
Other coolant temperature codes stored alongside

Possible causes

Damaged, corroded or loose wiring or connector at the radiator coolant temperature sensorlikely
Faulty radiator coolant temperature sensor (reading drifted or failed)likely
Low coolant level or air in the cooling system giving a false or unstable readingpossible
Thermostat stuck open or closed, so the reading does not match the engine temperaturepossible
Short or open circuit in the sensor signal or reference wiring, or a poor earthpossible
Fault in the control unit or its sensor reference supplyrare

How to diagnose

Read all stored codes and freeze frame data, noting coolant temperature and engine conditions when the code set, and check for other temperature sensor codes.
Check the coolant level and condition when the engine is cold, and look for leaks.
Inspect the sensor, its connector and the wiring for damage, corrosion, water ingress or chafing.
With a scan tool, compare the radiator sensor reading with the engine coolant temperature reading on a cold engine; they should be close.
Watch the live reading while the engine warms up and check it rises smoothly without jumps or dropouts.
Check the sensor resistance against the manufacturer's temperature table, and test the wiring for continuity, shorts and the reference voltage using the model-specific wiring diagram.
Check the thermostat operation and cooling fan control if the readings point to a real temperature problem.
Clear the code and road test to see whether it returns.

How to fix

Repair or replace damaged wiring, and clean or replace corroded connector terminals.
Replace the radiator coolant temperature sensor if its readings are out of specification.
Top up and bleed the cooling system, and repair any leak found.
Replace a faulty thermostat.
Repair the signal, reference or earth circuit fault found during testing.
Only after all else is ruled out, diagnose the control unit following the manufacturer's procedure.

Can I keep driving?

Medium severity

The car can usually be driven for a short time, but get it checked soon because the control unit may be using a default temperature and cooling fan control may be affected. Stop driving if the temperature gauge rises abnormally or you see signs of overheating.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.