Function
The ECT sensor is located in the small coolant circuit of the engine and measures the coolant temperature. The voltage value supplied by the ECT sensor is assigned to a corresponding temperature value by the PCM.
The ECT is used for the following calculations:
• Idle speed,
• Injection timing,
• Injected fuel quantity,
• EGR quantity,
• Glow plug control
• Actuation of the temperature gauge and glow-plug warning indicator
• Fan control
Effects of faults
In the event of a fault, the PCM operates using a substitute value (based on the IAT and fuel temperature). This calculated substitute value serves as an initial value. To this value, the PCM adds the value of the additional temperature increase every 10 seconds until the maximum limit of the PCM substitute value is reached. During this phase, the EGR quantity is already significantly reduced.
When the substitute value limit is reached, the EGR system is switched off and the engine power output is reduced (by reduction of the injected fuel quantity).
Further interventions in the case of a faulty ECT sensor:
• activation of a limited operation strategy on vehicles with thermo management (described in this lesson).
• shutting off of the electric PTC booster heater (not on all versions),
• switching on of the cooling fan,
• turning off of the air conditioning.
Diagnosis
With regard to exhaust gas emissions, the ECT sensor plays a very important part, as this value has a significant influence on the injected fuel quantity and EGR.
Moreover, the ECT sensor signal is used to define the warm-up cycle.
Monitoring of the ECT sensor consists of three parts:
• Monitoring for short circuit and open circuit,
• Monitoring of the signal for logical temperature increases,
• Monitoring for plausibility.
Faults in the EGR sensor have serious effects on the exhaust gas emissions. Therefore, this is a MIL active component.
Possible diagnostic trouble codes: P0115, P0116, P0117, P0118, P0119.