Ambient Air Temperature

Ambient Air Temperature

Description

The ambient air temperature signal is supplied by the instrument pack. The ECM performs two diagnostic checks on the signal.

Rationality Check

The signal is check for rationality against the IAT sensor. When the entry conditions have been met the difference between the sensors is checked, if this is greater than 15 degree C for a predefined period then a failure is registered. If the problem occurs on two drive cycles then the MIL will illuminate. Which DTC logs depends on whether the ambient air temperature sensor signal is lower or higher than the intake air temperature sensor.

Range/ Performance

If the instrument pack detects a failure in the ambient air temperature sensor it will output a constant default value . The range / performance check monitors for the signal being stuck at this default value for longer than a predefined period. When this occurs a failure is registered. If the problem occurs on two drive cycles then the MIL will illuminate.