Ambient Air Temperature (AAT) Monitoring

14.5 Ambient Air Temperature (AAT) Monitoring

14.5.1 CAN based Ambient Temperature - signal diagnosis

14.5.1.1 General Description
The purpose of this diagnosis is to detect electrical faults as defined in OBD I requirements. The input signal is a CAN message of instrumentation cluster. If an error is present on CAN signal such as CAN timeouts or the sensor detects a short circuit, an error is set.

14.5.1.3 Error Symptoms
- Signal error
- Short to battery or open circuit
- Short to ground

14.5.1.4 Flowchart: CAN based Ambient Temperature - signal diagnosis






14.5.2. Ambient Air Temperature Plausibility Check

14.5.2.1 General Description
This diagnosis is performed in order to detect a stuck or not-plausible AAT signal. The AAT sensor-signal is delivered via CAN by the instrument cluster

The diagnosis basically involves the comparison of the AAT sensor-signal to a model-AAT value which is calculated based on IAT-signal and other factors like MAF, engine-speed and vehicle speed. If the conditions for learning the AAT-model are fulfilled, then the difference between measured value and model value is monitored. If this difference exceeds a calibrate able threshold, an error is set.

14.5.2.3 Error Symptoms
Signal not plausible

14.5.2.4 Flowchart of Ambient Air Temperature Rationality Diagnosis