Audi Workshop Service and Repair Manuals

• ◆ To localise faults, the turbocharger (without boost pressure control) must be checked first and then the boost pressure with boost pressure control.
• ◆ A modified injection system is fitted on vehicles 07.97 ä, on which the connection hose to engine control unit is discontinued. The turbocharger tester cannot be connected to this injection system. The boost pressure can only be checked using fault reader V.A.G 1551.
• ◆ This section describes the test using both measuring devices.

Special tools, testers and auxiliary equipment required

• ◆ V.A.G 1397 A (only for vehicles ä 06.97)

• ◆ VAS 5051

or

• ◆ V.A.G 1551 with V.A.G 1551/3 A

Test sequence

• ‒ → On vehicles ä 06.97, disconnect connecting hose between rear air duct pipe and engine control unit and connect to T-piece of turbocharger tester V.A.G 1397 A.
• ‒ Route measuring hose under rear edge of bonnet and into passenger compartment via right hand window.

Testing without boost pressure control:

• ‒ → Pull connector -arrow- off solenoid valve for boost pressure control.

• ‒ → Switch on turbocharger tester and set measuring range selector switch to position -I- (absolute pressure).
• ‒ Connect measuring hose to connection -I-.

Notes:

• ◆ Hose connections must be completely airtight, otherwise measurements will not be correct.
• ◆ Ensure that measuring hose is not pinched at bonnet or side window.

• ◆ Pressing memory key M on turbocharger tester will store the last measured value until memory key M is pressed again or tester is switched off.
• ◆ The decimal point in the display flashes to indicate that the value is being stored.
• ◆ If the battery voltage of the turbocharger tester drops below the minimum level, an arrow will appear at the top left of the display.
• ◆ Observe safety precautions .

• ‒ Read measured value block, display group 011:

=> Diesel direct-injection and glow lamp system (4-cyl.) ä 06.97; Repair group 01; Self diagnosis of diesel direct-injection system; Reading measured value block

=> Diesel direction-injection and glow lamp system (4-cyl.) 07.97 ä; Repair group 01; Reading measured value block

• ‒ Measure the boost pressure at full throttle.
• ‒ Accelerate from 2000 rpm at full throttle in third gear (or with selector lever at position 2), and watch rev counter.
• ‒ Press PRINT key on V.A.G 1551 and memory key M on V.A.G 1397 A simultaneously at approx. 3000 rpm.

Specified values:

• ◆ → Specified value on V.A.G 1397 A:
  1.550 ... 1.750 bar

Notes:

• ◆ On vehicles ▸ 06.97, boost pressure level is measured with turbocharger tester V.A.G 1397/A. Fault reader V.A.G 1551 is then used to check whether boost pressure is being registered by the control unit.
• ◆ On vehicles 07.97 ▸ boost pressure can only be checked using V.A.G 1551.

• ‒ If measured boost pressure is OK, repeat boost pressure measurement with boost pressure control => Page 21-15.

If the boost pressure is not obtained:

• ◆ Leak between turbocharger and intake pipe
• ◆ Fault on linkage or vacuum unit for boost pressure control. Checking => Page 21-23
• ◆ Turbocharger defective (turbine sticking because of foreign body)

If boost pressure is exceeded:

• ◆ Boost pressure control hoses fallen off, leaking or clogged
• ◆ Solenoid valve for boost pressure limitation blocked
• ◆ Actuator (linkage, shaft) of bypass valve stiff or stuck (bypass valve always closed)

Testing with boost pressure control:

• ‒ Attach connector at solenoid valve for boost pressure limitation -N75.
• ‒ Erase fault memory.

Note:

A fault was recorded in fault memory due to disconnecting solenoid valve for boost pressure limitation -N75 when previous test was carried out.

• ‒ Read measured value block, display group 011.

• ‒ Measure the boost pressure at full throttle.
• ‒ Accelerate from 2000 rpm at full throttle in third gear (or with selector lever at position 2), and watch rev counter.
• ‒ Press PRINT key on V.A.G 1551 and memory key M on V.A.G 1397 A simultaneously at approx. 3000 rpm.

Specified values:

• ◆ → Specified value on V.A.G 1397 A:
  1.800 ... 2.050 bar

If the boost pressure is not obtained:

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

If boost pressure is exceeded:

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