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Diagnostic trouble code P1549

Diagnostic trouble code P1549

Boost pressure control valve

Symptom of fault

The needle of the Turbo/APC gauge goes far into the red zone. The pressure switch has opened.

Conditions




• The control module has reduced boost pressure by the maximum amount

• The pressure switch has opened


Diagnostic help

The boost pressure control valve can be activated by means of the ISAT scan tool.


- Connect an ISAT scan tool.



- Select "ACTIVATE".



- Select "BOOST PRESS. VALVE".


Checking the wiring. Intermittent faults may occur as a result of occasional short circuits and breaks in the wiring. Jiggle the leads and in-line connectors at several places and in different directions to reveal faults in the wiring harness. Observe the multimeter, ISAT scan tool or test lamp while carrying out this check.

Diagnostic procedure

1. Check additional diagnostic trouble codes in the Trionic system




- Read out all the diagnostic trouble codes with the ISAT scan tool. P0105 - P0108


Are any of the above diagnostic trouble codes present?

yes

Continue fault diagnosis as described for the appropriate diagnostic trouble code.


no

Continue with point 2.


2. Investigate the cause of the fault


In the following it will be determined 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 to each other with a length of pipe.



- Drive the car.



- Only basic boost pressure should be obtained when driving at wide open throttle from low engine rpm and when opening the throttle suddenly at higher engine rpm.


Is only basic boost pressure obtained?

yes

Continue with point 3.


no

Check and, if necessary, rectify the following:

• Binding wastegate

• Defective diaphragm unit

• Defective or incorrectly connected control hoses

• Incorrect or poorly adjusted basic boost pressure

Rectify as necessary and continue with point 9.


3. Check fuse 24




Is the fuse OK?

yes

Continue with point 4.


no

Continue with point 6.


4. 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 5.


no

Rectify the fault and continue with point 9.


5. Check the power supply



- Ignition switch in ON position.



- Check that the valve is supplied with power (+54 circuit) by connecting a test lamp to pin 2 of the valve's connector and a good grounding point.


The test lamp should light up.

Is the test lamp on?

yes

Continue with point 6.


no

Repair or replace the lead between pin 2 of the connector and fuse 5. Then continue with point 9.


6. 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 7.


no

Change the boost pressure control valve and continue with point 9.


Important

If there is a short circuit in any winding the control module will probably also be damaged. If a new valve is then fitted it will inevitably be rendered unserviceable. In the event of a short circuit, both valve and control module must therefore be changed at the same time .


If necessary, change fuse 24 afterwards.

7. Check the lead connected to pin 3 of the valve



- Ignition switch in 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 the lead between pin 3 of the valve's connector and pin 2 of the control module. Repair or replace the lead if necessary. Continue with point 9.


8. Check the lead connected to pin 1 of the valve



- Ignition switch in ON position.



- Plug in the valve's connector.



- Select "ACTIVATE".



- Select "BOOST PRESS. VALVE".


A loud buzzing sound should be heard.

Can a sound be heard?

yes

Change the boost pressure control valve and continue with point 9.


no

Check the lead between pin 1 of the valve's connector and pin 26 of the control module. Repair or replace the lead if necessary. Continue with point 9.


9. Final check



- Clear the diagnostic trouble code.



- Perform a driving cycle:

• Warm up the engine.

• Accelerate at wide open throttle from 1500 rpm to at least 3000 rpm 6 times.



- Evaluation of the driving cycle: Check whether the diagnostic trouble code has recurred and whether the pressure switch has opened during the driving cycle.


Has the diagnostic trouble code recurred or has the pressure switch opened during the driving cycle?

yes

Proceed to .


no

The remedial measure taken was correct.


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