Faulty or drifting engine coolant temperature sensor, reading inaccurately; Faulty or drifting intake air temperature sensor, including one built into the air mass or MAP sensor on some engines; Corroded, loose or damaged connectors or terminals on either sensor circuit; Wiring fault such as high resistance, chafing or a short to another circuit or earth; Thermostat stuck open, so the engine warms slowly and the coolant reading does not follow the expected pattern; Low coolant level or air in the cooling system giving a false coolant reading; Fault in the engine control unit sensor input circuit.

P011B

Engine Coolant Temperature/Intake Air Temperature Correlation.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
1: AreaFuel and air metering
1B: FaultThe specific fault in that area

What it means

P011B is the generic code for a poor correlation between the engine coolant temperature (ECT) reading and the intake air temperature (IAT) reading. After a long cold soak, the engine control unit expects the two sensors to read close to each other and to ambient. If they differ by more than the allowed amount, or if one does not track as expected after startup, the code is set.

Symptoms

Malfunction indicator lamp on
Hard or extended cranking on a cold start
Rough idle or poor running when cold
Cooling fan running at the wrong time or constantly
Poor fuel economy
Temperature gauge reading oddly or not moving as expected

Possible causes

Faulty or drifting engine coolant temperature sensor, reading inaccuratelylikely
Faulty or drifting intake air temperature sensor, including one built into the air mass or MAP sensor on some engineslikely
Corroded, loose or damaged connectors or terminals on either sensor circuitpossible
Wiring fault such as high resistance, chafing or a short to another circuit or earthpossible
Thermostat stuck open, so the engine warms slowly and the coolant reading does not follow the expected patternpossible
Low coolant level or air in the cooling system giving a false coolant readingrare
Fault in the engine control unit sensor input circuitrare

How to diagnose

Read and record all stored and pending codes and the freeze frame data, noting coolant and intake air temperatures when the code set
Check for other temperature sensor codes, as these point straight to the faulty circuit
Check the coolant level and look for leaks or signs of air in the system
With the engine fully cold (cold soaked for several hours), compare live ECT and IAT readings with each other and with ambient temperature; they should be close
Inspect both sensor connectors and wiring for corrosion, damage, water ingress and poor terminal tension
Watch live data during warm-up to check the coolant reading rises smoothly and the intake air reading behaves plausibly, and compare against a known good reference thermometer
Measure sensor resistance and supply voltage and compare with the manufacturer's specification for your model, as values vary by engine
Check that the thermostat opens at the right time and the engine reaches normal operating temperature

How to fix

Replace the engine coolant temperature sensor if it reads out of range or fails resistance checks
Replace the intake air temperature sensor, or the air mass or MAP sensor if the IAT is integrated, as the model requires
Clean or repair corroded connectors and terminals, and secure them properly
Repair or replace damaged wiring between the sensors and the control unit
Replace a thermostat that is stuck open, then top up and bleed the cooling system correctly
Check for an updated engine control unit calibration only if the manufacturer lists one for this fault

Can I keep driving?

Low severity

The car can usually be driven for a short time while you book it in, as this is rarely an immediate danger. Keep an eye on the temperature gauge, and have it checked soon because a wrong coolant reading can affect fuelling, cold starting and cooling fan operation.

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