High Boost Pressure

High boost pressure


Fault symptoms
- Pressure switch opens at wide open throttle.
- The needle of the Turbo/APC gauge goes deep into the red zone.

Conditions
No diagnostic trouble code.

Diagnostic procedure




1 Investigate the cause of the fault
The following checking procedure will determine whether the fault is a control fault or a basic engine / turbo fault:
- Disconnect the air hoses marked "W" and "C" from the boost pressure control valve and connect them together with a length of pipe.
- Drive the car.
When accelerating at wide open throttle from a low engine speed and when accelerating suddenly from a higher engine speed, only basic boost pressure should be obtained.

Is basic boost pressure obtained?
YES Continue with point 2.
NO Check and, if necessary, rectify the following:
- binding wastegate
- defective diaphragm unit
- defective or incorrectly connected control hoses.




2 Check fuse 5

Is the fuse OK?
YES Continue with point 3.
NO Continue with point 6.

3 Check the air hoses
- Inspect the valve's three control hoses, making sure that they are in good condition and correctly connected.

Are the air hoses OK?
YES Continue with point 4.
NO Rectify the fault and then continue with point 10.

4 Check the power supply
- Check that the valve is supplied with power by connecting test lamp 86 11 857 to pin 2 of the valve connector and a good ground.
The test lamp should light up.

Did the test lamp light up?
YES Continue with point 5.
NO Check and if necessary repair or replace the lead between pin 2 of the connector and fuse 5.




5 Check the resistance of the valve
- Take resistance readings in the valve's connector across:
- pins 1 and 2
- pins 2 and 3.
- Nominal resistance is 3±1 Ohms in both cases.

Are the readings OK?
YES Continue with point 6.
NO Change the boost pressure control valve. Continue with point 10.

Note: If there is a short circuit in any winding the control module is probably also damaged. It a new valve is then fitted, it will be automatically damaged beyond repair. In the event of a short circuit the control module must therefore also be changed. If necessary, also change fuse 5.

6 Check the valve
- Ignition switch in the ON position.
- Plug in the valve's connector. A weak buzzing sound should be heard.

Can a sound be heard?
YES Continue with point 8.
NO Check and if necessary repair or replace the lead between pin 1 of the valve's connector and pin 10 of the control module. If the lead is OK, continue with point 10.




7 Check the valve's electrical connections
- Unplug the valve's 3-pin connector.
- Connect test lamp 86 11 857 to pins 2 and 3 of the connector.
The test lamp should not light up.
- Connect the ISAT scan tool and select command code 451.
The test lamp should light up.

Did the test lamp light up?
YES Continue with point 8.
NO Check the lead between pin 1 of the valve's connector and pin 10 of the control module. Repair or replace the lead if necessary. If the lead is OK, continue with point 10.

8 Check the valve's air passages
- Remove the valve and check visually that its ports are not clogged.

Is the valve clogged?
YES Change the boost pressure control valve and then continue with point 10.
NO Continue with point 9.




9 Check functionality
- Try fitting a replacement valve.

Result OK?
YES Change the boost pressure control valve and then continue with point 10.
NO Continue with point 10.

10 Carry out basic boost pressure adaptation
When boost pressure has been rectified, adaptation of the system should be carried out, see "Adaptation of the Turbocharger System".
Then continue with point 11.

11 Check functionality
Drive the car on test to see whether the fault symptoms persist.

Do they persist?
YES Continue as described under "Before Control Module Replacement". Service and Repair
NO The steps taken to rectify the fault were correct, or else the fault is of an intermittent nature.