Volkswagen Workshop Service and Repair Manuals

Notes:

• ◆ It is extremely important to keep to the tightening torque of 20 Nm to ensure the knock sensors perform perfectly.
• ◆ The knock sensor might misinterpret vibrations of loose components as knocking. Therefore check that engine ancillaries are securely mounted.
• ◆ Only gold-plated contacts may be used when servicing the knock sensor connector contacts.

Special tools, workshop equipment, testers, measuring instruments and auxiliary items required

• ◆ Hand multimeter V.A.G 1526 or multimeter V.A.G 1715
• ◆ Fault reader V.A.G 1551 or vehicle system tester V.A.G 1552 with cable V.A.G 1551/3
• ◆ Adapter set V.A.G 1594
• ◆ Test box V.A.G 1598/31
• ◆ Current flow diagram

Check conditions

• ● Self-diagnosis has detected a fault on the knock sensor , Interrogating and erasing fault memory.
• ● The engine speed must be at least 2500 rpm =>display group 28, display zone 1
• ● The engine load musts be at least 40.0 % =>display group 28, display zone 2
• ● Coolant temperature must be at least 85 °C, =>display group 28, display zone 3.

Functional check

• ‒ Connect fault reader V.A.G 1551 (V.A.G 1552). Start engine and select "Address word" 01 of engine control unit. When doing this the engine must be running at idling speed.
  (Connecting fault reader and selecting engine control unit .)

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

• ‒ Press keys 0, 2 and 8 for the "Display group number 28" and confirm entry with Q key.

Note:

Checking the knock sensors must be performed during a test drive because the diagnosis of the knock sensors is not activated until the engine speed exceeds 2500 rpm and the engine is loaded by more than 40 %.

• ‒ Carry out test drive with a 2nd person to observe display.

Observe the valid safety precautions when carrying out a test drive => Page 28-6 .

• ‒ Check specification for knock control in display zone 4.
       Specification: Sys. OK.
• ‒ Press ⇒key.
• ‒ Press keys 0 and 6 for the function "End output" and confirm entry with the Q key.
• ‒ Switch off ignition.

If the specification is not obtained:

• ‒ Check resistance and wiring of knock sensor => Page 28-20 .

Checking resistance and wiring of knock sensor

• ‒ Remove noise insulation tray.
• ‒ → Pull 2 pin connector off knock sensor (G61) -arrow-.

• ‒ → Measure resistance of knock sensor between contact 1 (signal) and contact 2 (earth).
       Specification: ∞ω

If the specification is not obtained:

• ‒ Replace knock sensor (G61) , item 8 .
• ‒ Interrogate fault memory, if necessary, repair any faults and then erase fault memory => Page 01-20 , interrogating and erasing fault memory.
• ‒ Erase the learnt values and adapt the engine control unit again=> Page 24-128 .

If the specification is obtained:

• ‒ → Connect test box V.A.G 1598/31 to control unit wiring harness. The engine control unit remains disconnected.

• ‒ → Check wiring for open circuit between test box and 2-pin connector referring to current flow diagram:
       Contact 1 and test box socket     109
       Contact 2 and test box socket     101
       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:

• ‒ Loosen knock sensor and tighten again to 20 Nm.
• ‒ Perform a test drive again and check knock control specifications on display.

Observe the valid safety precautions when carrying out a test drive => Page 28-6 .

• During the road test the following operating conditions must be fulfilled:
• ‒ The coolant temperature must exceed 80 °C .
• ‒ When the temperature is reached, the operating conditions
       Idling
       Part throttle
       Enrichment
       Full throttle
       Overrun
  must be attained several times.
• ‒ At full throttle the speed must exceed 3500 rpm.

• ‒ Again interrogate the control unit fault memory.

If the fault is still present:

• ‒ Replace knock sensor (G61) , item 8 .
• ‒ Interrogate fault memory, if necessary, repair any faults and then erase fault memory => Page 01-20 , interrogating and erasing fault memory.
• ‒ Erase the learnt values and adapt the engine control unit again=> Page 24-128 .