Loose, corroded or damaged connector at the radiator coolant temperature sensor; Chafed, stretched or intermittently open or shorted wiring between the sensor and the control unit; Failing radiator coolant temperature sensor with an unstable internal element; Air pockets in the cooling system or low coolant level causing unstable readings at the sensor; Poor earth or reference voltage supply shared with other sensors; Water ingress or heat damage to the harness near the radiator or fan area; Fault within the control unit itself.

P00B5

Radiator Coolant Temperature Sensor Circuit Intermittent/Erratic.

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
B5: FaultThe specific fault in that area

What it means

P00B5 is a generic code meaning the control unit has detected an intermittent or erratic signal from the radiator coolant temperature sensor circuit. The reading has jumped, dropped out or changed in a way that does not match real coolant behaviour, or it has briefly gone out of range and then returned. This sensor is separate from the engine coolant temperature sensor on many vehicles, and its location and use depend on the model and engine.

Symptoms

Engine warning light on
Cooling fan running constantly or at odd times
Temperature gauge fluctuating or behaving erratically (where fitted to this sensor)
Poor fuel economy
Possible rough running or hard starting on some models
Fault appearing and disappearing

Possible causes

Loose, corroded or damaged connector at the radiator coolant temperature sensorlikely
Chafed, stretched or intermittently open or shorted wiring between the sensor and the control unitlikely
Failing radiator coolant temperature sensor with an unstable internal elementlikely
Air pockets in the cooling system or low coolant level causing unstable readings at the sensorpossible
Poor earth or reference voltage supply shared with other sensorspossible
Water ingress or heat damage to the harness near the radiator or fan areapossible
Fault within the control unit itselfrare

How to diagnose

Read all stored codes and freeze frame data, noting engine temperature, load and whether the fault is current or stored
Check the coolant level and condition when the engine is cold, and look for leaks
Locate the sensor for this model and inspect its connector and wiring for corrosion, damage, chafing or heat damage
With the engine running, watch the live radiator coolant temperature reading and compare it with the engine coolant temperature reading, looking for spikes or dropouts
Wiggle-test the harness and connector while watching the live data for any sudden changes
Check the sensor resistance against the manufacturer's temperature specification, both cold and as it warms
Test the reference voltage, signal and earth circuits for continuity, shorts and voltage drop
Check for related codes on other coolant temperature sensors or the cooling fan circuits, which may point to a shared wiring or earth fault

How to fix

Clean, repair or replace the damaged or corroded connector terminals
Repair or replace the faulty section of wiring
Replace the radiator coolant temperature sensor if it reads erratically or is out of specification
Top up the coolant and bleed the cooling system using the correct procedure for the vehicle
Repair any poor earth or supply fault found in the circuit

Can I keep driving?

Medium severity

The car can usually be driven short distances, but fix it soon because the cooling fan control may be affected and overheating is possible. Watch the temperature gauge and stop if it rises abnormally.

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