Boost Pressure Regulation Checking

Special tools and equipment
- VAG 1551 scan tool (or VAG 1552 mobile scan tool) with VAG 1551/3 cable

Test requirements
- No leaks on intake or exhaust side
- Engine oil temperature at least 80 °C

Test sequence
- Connect VAG 1551 scan tool (VAG 1552). Start engine and select the Engine Control Module (ECM) using address word 01. Connecting scan tool and selecting Engine Control Module (ECM):
See VAG 1551, connecting and selecting control module for engine electronics. Refer to "On Board Diagnostic". Testing and Inspection

Indicated on display


Rapid data transfer HELP
Select function XX

- Press buttons -0- and -8- to select "Read measuring value block" function 08. Press -Q- button to confirm input.

Indicated on display


Read Measuring Valve Block HELP
Input display group number XXX


- Press 1,1 and 4 for the function "display group number 114", and then press Q to exit from input mode.

Indicated on display


Read Measuring Valve Block 114 ->
1 2 3 4


- Check duty cycle of wastegate bypass regulator valve during a road test or on a chassis dynamometer (at Wide Open Throttle between 1800 and 2300 RPM) in display field 4
Specification: 5-95 %

If specified value is obtained:
- Press button -3- (VAG 1551) or up arrow button (VAG 1552).
- Press 1,1 and 5 for the function "display group number 115", and then press 0 to exit from input mode.

Indicated on display


Read Measuring Value Block 115 ->
1 2 3 4


- Check actual charge pressure value in display field 4 at Wide Open Throttle (WOT):

On dynamometer
In 3rd gear or in 2nd drive mode

While driving
Vehicles with manual transmission
- Accelerate vehicle at Wide Open Throttle (WOT) in 2nd gear

Vehicles with automatic transmission
- Manually place vehicle in 4th gear and accelerate vehicle from low speed at Wide Open Throttle (without kick down, transmission does not downshift any more).
- Press the print button between 1800 and 2300 RPM and check the actual boost pressure value in display field 4.
Specification: 1350 to 1750 mbar
- Compare actual boost pressure with specification in display field 3 Difference: max. 100 mbar


NOTES: Repeat measurement if boost pressure was not fully charged or if the difference between actual and specified values was too large.


If boost pressure is exceeded:
- Check charge air pressure sensor -G31-. Testing and Inspection
- Check wastegate bypass regulator valve -N75-. (Throughput in hose from turbocharger via valve to vacuum diaphragm with connector disconnected)
- Check for proper seating of vacuum diaphragm for wastegate bypass regulator valve at turbocharger.
- Check vacuum diaphragm. Testing and Inspection
- Check bearing for shaft of wastegate bypass regulator valve in turbocharger for ease of movement.
If rusted solid, replace turbocharger.

If boost pressure is not reached:
- Check charge air pressure sensor -G31-. Testing and Inspection
- Check wastegate bypass regulator valve -N75-.
- Check bearing for shaft of wastegate bypass regulator valve in turbocharger for ease of movement.
If rusted solid, replace turbocharger.
- Turbocharger malfunctioning, replace.