Pressure Sensor: Test

Select "READ MEASURING VALUE BLOCK" function 08 using (VAG 1551) Scan Tool. See READING/MEASURING VALUE BLOCK (FUNCTION 08) under OUTPUT DIAGNOSTIC TEST MODES (DTM) in SELF-DIAGNOSTICS article.
Input display group number 02. Observe display value in channel 4.

NOTE: The air pressure value detected by the pressure sensor reflects altitude, as well as any pressure variations due to weather. Weather related fluctuations are generally under ±50 mbar, except in extreme conditions or in tropical climates. At sea level, the air pressure under standard weather conditions is about "1013 mbar" and decreases by approximately "100 mbar per 1000 meters" (3281 ft) of elevation.

If 986 mbar is constantly displayed (or if display value differs significantly from the expected):

Check voltage supply to pressure sensor.
Check circuit wiring and connections.
If the pressure sensor fails, the Engine Control Module (ECM) will automatically assume an air pressure value equivalent to an altitude of 30 meters (98.4 ft). This default value yields an air pressure reading of "968 mbar" which displays continuously.
Since the default value will also cause a malfunction to be stored in Diagnostic Trouble Code (DTC) memory, the DTC memory must be erased once the malfunction is repaired. Note, however, that erasing the DTC memory will not erase the default value assumed by the ECM. Erase the default pressure value as follows:
Switch ignition OFF.
Disconnect ECM circuit breaker S64 for 30 seconds (Red holder, position 3, 15 Amp rating). See Figure.