P1549

BOOST PRESSURE CONTROL VALVE (APC 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 APC valve can be activated with the ISAT scan tool.
- Connect an ISAT scan tool.
- Select "ACTIVATE".
- Select "BOOST PRESS. VALVE".





Diagnostic Procedure.
1. Check additional diagnostic trouble codes in the Trionic system
- Obtain readouts of all diagnostic trouble codes using 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
^ Incorrectly adjusted basic boost pressure Rectify as necessary and continue with point 9.




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. Check the lead between pin 3 of the valve's
NO:
^ 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 at "Before Replacing a Control Module". Component Tests and General Diagnostics
NO
^ The remedial measure taken was correct.