Audi Workshop Service and Repair Manuals

Checking turbocharger and charge pressure regulating valve - engine codes AEB, AJL Special tools and workshop equipment required

t  Turbocharger tester -V.A.G 1397A-

Procedure l  All hoses and pipes securely fitted and and free of leaks. l  Fault memory interrogated, final control diagnosis performed → Vehicle diagnosis, testing and information system VAS 5051. –  Connect T-piece with hose of turbocharger tester -V.A.G 1397A- to intake manifold (front). –  Route test hose under rear edge of bonnet and through right window into passenger compartment.

–  Switch on turbocharger tester and set measuring range selector switch to position -I- (absolute pressure). –  Fit test hose to connection -I-.   Note t  Ensure absolute leakproof connection of hoses to avoid measurement errors. t  Take care not to trap test hose at bonnet and side window. t  Pressing memory button -M- on turbocharger tester causes last measured value to be stored until memory button -M- is pressed again or tester is switched off. t  The decimal point in the display flashes to indicate that the value is being stored. t  If the battery voltage of the turbocharger tester drops below the minimum level, an arrow will appear at the top left of the display. t  Before performing the test, drive vehicle moderately fast for at least 3 km (without stopping at traffic lights etc.).   WARNING Accidents can be caused if the driver is distracted by test equipment while road-testing, or if test equipment is not properly secured. Observe safety precautions → Chapter. l  Charge pressure is measured under full load while driving or on a roller dynamometer. l  Test duration per measurement: max. 10 seconds l  Engine running.

Vehicles with engine code AEB: –  Accelerate vehicle in 3rd gear (or position 2) from 2000 rpm at full throttle while a second mechanic observes the rev counter. –  Second mechanic should press memory button -M- on -V.A.G 1397A- at approx. 3000 rpm. l  Specification: 1.370 ... 1.470 bar.

Vehicles with engine code AJL: –  Accelerate vehicle in 3rd gear (or position 2) from 2000 rpm at full throttle while a second mechanic observes the rev counter. –  Second mechanic should press memory button -M- on -V.A.G 1397A- at approx. 2500 rpm. Display on -V.A.G 1397 A-: l  Specification: 1.800 ... 1.900 bar. All vehicles (continued):

If specification is not obtained:

Fault	Possible causes
Charge pressure below specification	t  Hose connections to charge pressure control solenoid valve -N75- defective. Connection diagram → Chapter t  Charge pressure control solenoid valve -N75- defective. Checking → Chapter t  Charge pressure regulating valve in turbocharger stuck in open position. Renew turbocharger → Chapter t  Leaks between turbocharger and intake manifold (air intake hoses and vacuum hoses). Effects → Chapter t  Mechanical air recirculation valve defective. Checking → Chapter t  Turbocharger defective. Renewing → Chapter
Charge pressure above specification 1)	t  Air leaks in hoses or connections to pressure unit for charge pressure control (via -N75-). Connection diagram → Chapter t  Vacuum unit for charge pressure regulating valve defective. Renew turbocharger → Chapter t  Charge pressure regulating valve in turbocharger sticking in closed position. Renew turbocharger → Chapter
l  1) If the charge pressure is too high the fuel supply will be shut off in order to protect the engine. Misfiring will then occur at high engine speeds.

Checking load signal in order to test charge pressure control function   Note On vehicles with automatic gearbox the charge pressure test is not always a reliable indication of the proper function of the charge pressure control system. Therefore, if the pressure value is close to the lower tolerance limit, check the load signal in order to test the charge pressure control function.   WARNING Accidents can be caused if the driver is distracted by test equipment while road-testing, or if test equipment is not properly secured. Observe safety precautions → Chapter. l  Vehicle diagnostic, testing and information system -VAS 5051B- connected. l  Engine running. l  Vehicle self-diagnosis and vehicle system “01 - Engine electronics” selected.

Display on -VAS 5051B-: –  From menu -1-, select diagnosis function “Measured values” and press → key to continue.

Display on -VAS 5051B-: –  Press keys 25 on keypad -1- to select “Display group 025” and confirm entry by pressing Q key.

Display on -VAS 5051B-: –  Accelerate vehicle at a constant rate and check display in display zones -2- and -3-. l  Specification: maximum difference between indicated values: 0.3 ms.   Note If the self-diagnosis function of the engine control unit detects a fault in the charge pressure control system, the duty cycle in display zone -4- is set to 5% (constant). If the specification is not attained → Anchor.