Volkswagen Workshop Service and Repair Manuals

Special tools, workshop equipment, test and measuring appliances and auxiliary items required

• ◆ V.A.G 1390 Vacuum pump
• ◆ V.A.G 1526 Hand multimeter
• ◆ V.A.G 1594 A Adapter set
• ◆ V.A.G 1598/31 Test box
• ◆ Fault reader V.A.G 1551 or vehicle system tester V.A.G 1552 with cable V.A.G 1551/3
• ◆ Current flow diagram

Check conditions

• ● No fault stored in fault memory

=> Repair group 01; Self-diagnosis; Interrogating and erasing fault memory

• ● No leaks on intake and exhaust systems.
• ● Control pipe to charge pressure regulating valve is not blocked, loose or leaking.
• ● No faults in engine and fuel injection system
• ● Engine oil temperature min. 80 °C

Test sequence

Observe following if test and measuring instruments are required during a test drive:

• ◆ Test and measuring instruments must be secured to rear seat and operated by a 2nd person from this location.

• If test and measuring instruments are operated from front passenger's seat and the vehicle is involved in an accident, there is a possibility that the person sitting in this seat may receive serious injuries when the airbag is triggered.

• ‒ The charge pressure is measured with the fault reader V.A.G 1551 during a test drive.

To enable the charge pressure control to be checked it is essential that the charge pressure is first determined with charge pressure control deactivated.

• ‒ → Pull off charge pressure control solenoid valve (N75) -1- connectors -2-.
• ‒ With engine running at idle speed, connect fault reader V.A.G 1551 (V.A.G 1552) and select engine electronics control unit with the "Address word" 01:

=> Repair group 01; Self-diagnosis; Connecting fault reader V.A.G 1551 and selecting engine electronics control unit

• ‒ Press keys 0 and 8 for the function "Read measured value block" and confirm entry with Q key.

• ‒ Press keys 0, 1 and 1 for display group 11 and confirm entry by pressing Q.

If the charge pressure is not attained:

• ‒ Check charge pressure control valve pressure unit and renew if necessary.
• ‒ Check vacuum hoses .
• ‒ Repeat charge pressure check.

If the charge pressure has still not been attained:

• ‒ Replace turbocharger.

If the charge pressure is exceeded:

• ‒ Test charge pressure control solenoid valve (N75). (Through-flow in hose from turbocharger via valve to pressure unit when connector is pulled off).
• ‒ Check vacuum hoses => Page 21-11.
• ‒ Check charge pressure control valve pressure unit as well as the operating rod and renew if necessary.
• ‒ Check shaft mounting for charge pressure regulating valve in turbocharger for ease of movement.
  When corroded together, renew turbocharger.
• ‒ If the measured charge pressure is OK., repeat charge pressure measurement with charge pressure control active:
• ‒ Connector connected to solenoid valve charge pressure control -N75.

Note:

Separating connector on solenoid valve for charge pressure control -N75- causes a fault to be recorded. Interrogate and erase fault memory.

• ‒ Interrogate fault memory:

=> Repair group 01; Self-diagnosis; Interrogating and erasing fault memory

• ‒ With engine running at idle speed, connect fault reader V.A.G 1551 (V.A.G 1552) and select engine electronics control unit with the "Address word" 01:

=> Repair group 01; Self-diagnosis; Connecting fault reader V.A.G 1551 and selecting engine electronics control unit

• ‒ Press keys 0 and 8 for the function "Read measured value block" and confirm entry with Q key.

• ‒ Press keys 0, 1 and 1 for display group 11 and confirm entry by pressing Q.

If the specification is not obtained:

• ‒ Check solenoid valve for charge pressure control (N75) => Page 21-22
• ‒ Check vacuum hoses => Page 21-11.

Checking solenoid valve for charge pressure control (N75)

• ‒ Switch off ignition.
• ‒ → Pull off charge pressure control solenoid valve (N75) -1- connectors -2-.
• ‒ Measure resistance between valve contacts.

Specification: 25...45ω

If the specification is not obtained:

• ‒ Replace charge pressure control solenoid valve (N75).

If the specification is obtained:

• ‒ Switch on ignition.
• ‒ → Measure valve's supply voltage at connector contact 1 and at engine earth.
      Specification: approx. battery voltage

If the specification is not obtained:

• ‒ Switch off ignition.

• ‒ → Connect test box V.A.G 1598/31 to control unit wiring harness. The engine control unit remains disconnected.
• ‒ Check wiring between test box and connector for open circuit using current flow diagram.
      Contact 1 + socket 1 and 2
      Contact 2 + socket 62
      Wire resistance: max. 1.5 ω
• ‒ Additionally check wires for short to one another, to vehicle earth and to battery positive.
      Specification: ∞ω

If no fault is detected in the wiring:

• ‒ Renew Diesel direct injection system control unit (J248)

=> Repair group 23; Renewing engine control unit, coding and matching; Renewing engine control unit