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Checking boost pressure for engine codes ALH, AHF > < Testing the boost pressure system

A3 Mk1

Diesel Direct Injection and Glow Plug System (TDI 4 cyl.) >07.99
Testing the boost pressure system
Test boost pressure - engine code AGR

In order to check the boost pressure control it is essential to first measure the boost pressure without boost pressure control

  • ‒ Remove the connector from the boost pressure control solenoid -N75 => Installation location overview- Page 23-3.
  • ‒ Checking boost pressure The boost pressure is measured with the fault reader V.A.G 1551 during a test drive.
Important:
Second person is required to operate V.A.G 1551.
  • ‒ Read measured value block, display group 11, Engine idling
 
→ Indicated on display:
Read measured value block 11    ⇒
    900 rpm    938 mbar    978 mbar    92 %    
  • ‒ Accelerate vehicle in 3rd gear from about 1500 rpm using full throttle.
  • ‒ Press PRINT key on V.A.G 1551 at about 3000 rpm.
     
    → Specification for display zone 3: 1550...1750 mbar
    Read measured value block 11    ⇒
        3040 rpm 1846 mbar    1693 mbar    39 %    

    If the measured boost pressure is too low, this may be due to the following:

    • ◆ Intake manifold pressure sender defective
    • ◆ Leak between turbocharger and intake manifold
    • ◆ Turbocharger defective (turbine sticking because of foreign body)
    • ◆ Bypass valve actuation (linkage, shaft) stiff or stuck (bypass valve permanently open)

    If the measured boost pressure is too high, this may be due to the following:

      • ‒ Boost pressure control hoses fallen off, leaking or clogged.
      • ‒ -N75 solenoid valve for boost pressure control blocked.
      • ‒ Actuator (linkage, shaft) of bypass valve stiff or stuck (bypass valve always closed)
      • ‒ Aneroid box leaking

    If measured boost pressure is OK, repeat boost pressure measurement with boost pressure control:

    • ‒ Connector on boost pressure control solenoid valve N75 is connected.
    • ‒ Read measured value block, display group 11, Engine idling => Page 01-75
     
    → Indicated on display:
    Read measured value block 11    ⇒
        900 rpm    938 mbar    978 mbar    92 %    
  • ‒ Accelerate vehicle in 3rd gear from about 1500 rpm using full throttle.
  • ‒ Press PRINT key on V.A.G 1551 at about 3000 rpm.
     
    → Specification for display zone 3: 1800...2050 mbar
    Read measured value block 11    ⇒
        3090 rpm     1866 mbar    1917 mbar    62 %    

    If the measured boost pressure is too low, this may be due to the following:

    • ◆ No electrical function of solenoid valve for boost pressure limitation.
    • ◆ Boost pressure control solenoid valve -N75 is stuck in the open position

    If the measured boost pressure is too high, this may be due to the following:

    • ◆ Solenoid valve for boost pressure limitation -N75 sometimes stuck closed.
    • ◆ boost pressure increased as a result of tuning

    Checking boost pressure for engine codes ALH, AHF > < Testing the boost pressure system