Checking knock sensor — AUDI

Notes:

It is extremely important to keep to the tightening torque of 20 Nm to ensure the knock sensors perform perfectly.
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

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 1598/22
Hand multimeter V.A.G 1526 or multimeter V.A.G 1715
Adapter set V.A.G 1594
Current flow diagram

Test conditions

Knock sensor fault recognised by self-diagnosis =>Page
01-16
, interrogating and erasing fault memory.

Test sequence

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 => Page
01-7
.)

Rapid data transfer
HELP
Select function XXX
Indicated on display:

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

Read measured value block
Input display group number XXX
Indicated on display:

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

Read measured value block 28
⇒
1
2
3
4
Indicated on display:
(1...4 = Display zones)

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: Syst. OK

If the specification is obtained:

Press ⇒key.
Press keys 0 and 6 for the "End output" function and confirm input with the Q key.

Switch off ignition.

If the specification is not obtained:

Checking resistances and wiring

Pull 2 pin connector off knock sensor -arrow-.

Measure resistance between the contacts 1+2 at connections to knock sensors.
Specification ∞ω

If the specification is not obtained:

Replace knock sensor (G61) =>Page
28-4
, item
5
.

If the specification is obtained:

Connect test box V.A.G 1598/22 to control unit wiring harness
=> Page
24-121
.

Check wires between test box and 2-pin connector (connector to control unit) for open circuit using current flow diagram.
Contact 1+socket 77
Contact 2+socket 63
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.
Carry out test drive again.

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
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) =>Page
28-4
, item
5
.