1.15.4.3 Rationality check

The first rationality check compares, during the current driving cycle, the change of the atmospheric pressure within a calibrated period of time. Under normal driving conditions e.g. uphill driving this change should be very slow.

If the absolute change of the measured pressure within a calibrated period of time exceeds a calibrated threshold for a calibrated period of time, a signal fault PUR will be set.

The second rationality check compares, during ignition on and engine off, the measured atmospheric pressure with the stored atmospheric pressure of the last driving cycle. After normal parking conditions (engine off) the difference between these two values should be very small. To cover special circumstances e.g. transportation from low to high altitude, the measured atmospheric pressure may additionally be compared after start of engine, with a modeled atmospheric pressure based on the mass airflow sensor. This additional check is only done if the signal change since the last driving cycle exceeds the threshold.

If...

• the absolute difference between the measured and stored atmospheric pressure exceeds a calibrated threshold (during ignition on and engine off) and
• the absolute difference between measured atmospheric pressure and modeled atmospheric pressure exceeds a calibrated threshold (during engine running),

all for a calibrated period of time, a plausibility fault PUR will be set.