Faulty radiator outlet or engine coolant temperature sensor giving a skewed or slow signal; Damaged wiring, corroded terminals or loose connector at either sensor; Low coolant level or air trapped in the system causing unreliable readings; Thermostat stuck open or closed, so the two temperatures differ more than expected; Weak coolant flow due to a failing water pump, blocked radiator or collapsed hose; Fault in the engine control unit or its sensor reference supply or ground.

P00B6

Radiator Coolant Temperature/Engine Coolant Temperature Correlation.

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
B6: FaultThe specific fault in that area

What it means

P00B6 is the generic code for a correlation fault between the radiator coolant temperature and the engine coolant temperature readings. The control unit compares the two sensor signals, and sets the code when they disagree by more than expected for the operating conditions, for example after a cold soak or once the engine is fully warm. The fault may lie with either sensor, their wiring, or the cooling system itself, and the exact strategy varies by model and engine.

Symptoms

Engine warning light on
Temperature gauge reading erratic, low or higher than normal
Cooling fan running constantly or at odd times
Poor heater output or slow warm-up
Rough running, higher fuel consumption or hard starting if the unit uses a default temperature value
Engine running hotter than normal in severe cases

Possible causes

Faulty radiator outlet or engine coolant temperature sensor giving a skewed or slow signallikely
Damaged wiring, corroded terminals or loose connector at either sensorlikely
Low coolant level or air trapped in the system causing unreliable readingspossible
Thermostat stuck open or closed, so the two temperatures differ more than expectedpossible
Weak coolant flow due to a failing water pump, blocked radiator or collapsed hosepossible
Fault in the engine control unit or its sensor reference supply or groundrare

How to diagnose

Read all stored codes and freeze frame data, noting coolant temperatures, engine load and run time when the code set
Check the coolant level when cold and inspect for leaks, contamination or signs of overheating
Inspect both sensors, their connectors and wiring for damage, corrosion, chafing or water ingress
Compare live data from both sensors on a fully cold engine, where they should read close to each other and to ambient temperature
Watch both readings during warm-up and check they rise in a believable way and that the fan operates when expected
Check the thermostat operation by feeling hose temperatures and comparing with live data, following the manufacturer's procedure
Measure the sensor resistance and signal voltage against specification for your model, and check the reference supply and ground at the connector
Check for coolant flow and radiator blockage if temperatures differ when hot

How to fix

Replace the faulty temperature sensor once testing confirms it is out of specification
Repair or replace damaged wiring and clean or renew corroded connectors
Top up and bleed the cooling system correctly, and fix any leak found
Replace a thermostat that is stuck or slow to operate
Repair or replace the water pump, hoses or radiator if flow is restricted
Check for a published software update only if the manufacturer lists one for this fault

Can I keep driving?

Medium severity

Short, careful journeys are usually possible if the temperature gauge stays normal, but book it in soon as the control unit may be working from poor temperature data. Stop at once if the engine overheats or the gauge climbs, as overheating can cause serious engine damage.

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