Volkswagen Workshop Service and Repair Manuals

Special tools, testers and auxiliary items

• ◆ Fault reader V.A.G 1551 or vehicle system tester V.A.G 1552 with cable V.A.G 1551/3
• ◆ Test box V.A.G 1598/18
• ◆ Hand multimeter V.A.G 1526 or multimeter V.A.G 1715
• ◆ Adapter set V.A.G 1594
• ◆ Current flow diagram

Functional check

• ‒ Connect fault reader V.A.G 1551 (V.A.G 1552) and select engine electronics control unit (address word 01); carry out selection with ignition switched on.
  

• ‒ Input 08 for "Read measured value block" function and confirm with Q.

• ‒ Enter 03 for "Display group number" and confirm with Q.

Note:

If something different is indicated on the display:

=> Fault reader operating instructions

• ‒ Check throttle valve angle on idling speed stop, in display zone 3.
       Specification: 5...19 <°
• ‒ Slowly open throttle valve fully and observe angle displayed in display zone 3.
  The figure must increase uniformly over
       the complete range.
• ‒ Check throttle valve angle at full throttle stop in display zone 3.
       Specification: 85...101 <°
• ‒ Press ⇒ key.
• ‒ Input 06 for "End output" and confirm with Q.
• ‒ Switch off ignition

Note:

The displayed figure is dependent on the tolerances of the throttle valve potentiometer and does not correspond to the actual opening angle.

If the figure does not increase uniformly:

• ‒ Replace throttle valve potentiometer.

If the figure remains constant:

• ‒ Continue check according to following table.

Checking voltage supply

• ‒ → Separate 3 pin connector to throttle valve potentiometer.
• ‒ Connect multimeter to measure voltage at contacts 1+3 of connector.
• ‒ Switch on ignition.
       Specification: min. 4.5 V
• ‒ Switch off ignition

If the specification is not obtained:

• ‒ → Connect test box V.A.G 1598/18 to control unit wiring loom.

• ‒ → Check wiring between test box and 3 pin connector for open circuit according to current flow diagram.
       Contact 1+socket 41
       Contact 3+socket 33
       Wire resistance: Max. 1.5 ω
• ‒ Check wiring at 3 pin connector for short to one another.
       Contact 1+socket 33
       Specification: ∞ω

If no wiring fault is detected:

• ‒ Renew Motronic control unit (J220)
  => Page 24-9 , item 16 .

Checking wiring

• ‒ → Connect test box V.A.G 1598/18 to control unit wiring loom.

If the display shows constant 0 <°:

• ‒ Check wire for short to earth.
       Sockets 01+40
       Specification: ∞ω

If the display shows constant 106 <°:

• ‒ Switch on ignition.
• ‒ Check wire for short to positive, to do this connect multimeter to measure voltage at test box sockets 01+40
       Specification: 0 Volt
• ‒ Switch off ignition

Continuation if voltage is present:

If voltage of about 5 V was present:

• ‒ Separate 3 pin connector to throttle valve potentiometer.
• ‒ Switch on ignition.

• ‒ → Check wiring at 3 pin connector contacts 1+2 for short to one another according to current flow diagram.
       Specification: ∞ω

If the voltage was approx. battery voltage:

• ‒ Check wire at 3 pin connector contact 1 for short to battery positive according to current flow diagram.

Continuation if no voltage is present:

• ‒ Separate 3 pin connector to throttle valve potentiometer.
• ‒ Check wiring between test box and 3 pin connector for open circuit according to current flow diagram.
       Contact 2+socket 40
       Wire resistance: Max. 1.5 ω

If no wiring fault is detected:

• ‒ Replace throttle valve potentiometer.