DTC P011B: Engine Coolant Temperature/Intake Air Temperature Correlation: Description

The engine has two temperature sensors, an Engine Coolant Temperature (ECT) sensor and an Intake Air Temperature (IAT) sensor, to detect the temperature while the engine is in operation. A thermistor, whose resistance value varies according to the temperature, is built into each sensor. When the temperature is low, the resistance of the thermistor increases. When the temperature is high, the resistance drops. These variations in resistance are transmitted to the ECM as voltage changes. Based on these temperature signals output from the sensors, the ECM determines the fuel injection duration and the ignition timing to control the engine.

DTC No.	DTC Detection Condition	Trouble Area
P011B	All of the following conditions are met (2 trip detection logic): The battery voltage is 10.5 V or higher. 7 hours or more have elapsed since the engine stopped on the previous trip. 15 seconds or more after a cold engine start. Either of the following conditions is met: The minimum intake air temperature after the engine starts is -10°C (14°F) or more. The engine coolant temperature before the engine starts is -10°C (14°F) or more. The difference between the readings of the engine coolant temperature and intake air temperature is more than 20°C (36°F).	IAT sensor ECT sensor ECM

Fig 1: Identifying Difference Between Engine Coolant & Intake Air Temperature Graph

HINT:

Waiting is required to prevent the temperature of the engine from affecting the readings. If the engine has been operated recently, it will not be possible to accurately compare the readings.
For diagnosis, in order to duplicate the detection conditions of the DTC, it is necessary to park the vehicle for 7 hours. Parking the vehicle for 7 hours ensures that the actual temperature of the ECT and IAT are very similar. When the vehicle has been parked for less than 7 hours, differences in the readings may exist, this does not necessarily indicate a fault.