Testing altitude sender - engine code AEB — AUDI

AEB
The signal from the altitude sender influences

the boost pressure control

The boost pressure control prevents the turbocharger from over-revving when the altitude increases and consequently the air density decreases.
Due to the reduction in air density (reduction in air pressure), the turbocharger needs to work harder (higher rotational speed) to deliver the required boost pressure.
This results in a higher charge air temperature and an increased risk of engine knocking. To avoid this, the boost pressure is limited.

Mixture composition during engine start:

The richness of the starting mixture is preset by map data in the Motronic control unit and corrected with increasing altitude (decreasing air density due to decreasing air pressure) by a "lean" adjustment determined by the altitude sender.

Note:

The altitude sender is located in the electronics box next to the Motronic control unit.

Testing altitude sender signal

Read individual measured value (function 09) and select channel 06.

Read individual measured value
⇒
Channel 06
measured value
193
Display:

Specifications:

Altitude: / in m · Air pressure in mbar · Signal voltage · Channel 06 / Measured value
0 · 1013 · 4.0 V · 204
400 · 970 · 3.7 V · 188
1000 · 900 · 3.0 V · 153
2000 · 800 · 2.1 V · 107
3000 · 700 · 1.3 V · 66

Pressure variations due to weather changes are not taken into account.

Measure the current air pressure using turbocharger tester V.A.G 1597/A (absolute pressure display) and compare it to the measured value from channel 06.
If the measured value from channel 06 deviates so much that it seems implausible for the altitude / air pressure, check the wiring for contact resistance and if necessary, replace the altitude sender.

Checking wiring

Note:

The altitude sender is monitored by the self-diagnosis system =>Fault table, fault code 00528 - Page

Disconnect the plug from the altitude sender.
Measure the voltage with a hand-held multimeter V.A.G 1526 in turn between the contacts 1 + 3 and 2 + 3.

Specified value: 4.5...5.5 V in each case

If one of the specified values is not met turn off the ignition.

Connect test box V.A.G 1598 with adapter cable V.A.G 1598/19 to the wiring harness for the Motronic control unit.

Check the following wiring connections for continuity and short circuits according to the current flow diagram:

3-pin connector, / contact · V.A.G 1598/19, / socket
1 · C9
2 · C6
3 · C2

If necessary rectify open circuit or short circuit according to the current flow diagram
If the wiring is OK replace the altitude sensor.
If after replacing the altitude sensor an implausible value is obtained again, replace the Motronic control unit.