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 1551/1
• ◆ Hand multimeter V.A.G 1526 or multimeter V.A.G 1715
• ◆ Adapter set V.A.G 1594
• ◆ Current flow diagram

Test sequence

• ‒ Connect the fault reader V.A.G 1551 (V.A.G 1552) and with ignition switched on select Diesel pump electronics control unit with the "Address word" 41.
  (Connecting fault reader 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 and 1 for "Display group number 01" and confirm entry with Q key.

• ‒ Read off voltage value in display zone 2.
       Specification: At least 0.2 V
• ‒ Slowly open throttle to full throttle position and observe the voltage indicated in display zone 2. The voltage must increase uniformly over the whole range.
       Specification: Max. 4.8 V
• ‒ Press the ⇒key.
• ‒ Press keys 0 and 6 for the "End data transfer" function and confirm input with the Q key.
• ‒ Switch off ignition.

If the voltage does not increase uniformly:

• ‒ Renew injection pump .

If the voltage increases uniformly but is not within the specification limits:

• ‒ Check governed speed
• ‒ Check wire to load signal potentiometer between automatic glow period control unit (J179) and 19 pin connector for transfer resistances according to current flow diagram (control unit pulled out).
       Wire resistance: Max. 1.5 ω

If no wiring fault is detected and the governed speed is OK:

• ‒ Renew injection pump .

If voltage remains constant:

• ‒ Switch off ignition.
• ‒ Separate multi-pin connector.

• ‒ → Connect multimeter to measure voltage at connector contacts 12+15.
• ‒ Switch on ignition.
       Specification: min. 4.9 V
• ‒ Switch off ignition.
• ‒ Check wire to load signal potentiometer between automatic glow period control unit (J179) and multi-pin connector for open circuit according to current flow diagram (control unit pulled out).
       Wire resistance: Max. 1.5 ω
• ‒ Additionally check wires for short to one another.
       Specification: ∞ω

If the voltage supply and wirings are OK:

• ‒ Renew injection pump .

If no wiring fault is detected and a minimum voltage of 4.9 V was not present between contacts 12+15:

• ‒ Renew automatic glow period control unit (J179) , item 4 .