Knock Sensor or Timing Sensor ?

Kent McLean kentmclean at
Mon May 24 10:07:26 EDT 2004

Cat ^. .^ ~ wrote:
> 1.  Are the knock sensors (white and red) interchangeable ?
> One code we found was the second knock sensor code and the parts people 
> tell us there is only one knock sensor... and the Bentley manual says 
> there are two and there are TWO in the car ???

Some MC engines have two knock sensors. If the parts people
say there is only one part number, chances are Audi used the
same part to test for knock on different areas of the engine.
(And if I'm wrong, someone please speak up.)

> 2.  Is there a way to test them individually off of the car ?

For an on the car test, the archives showed this:

It uses an oscilloscope, but I'm guessing (And if I'm wrong...)
that the knock sensor just puts out some small voltage or
changes resistance when knock is present. Put a voltmeter
or ohm meter on the leads, whack the engine block with a
hammer (gently; you don't want to put a hole in the block)
and see if it registers a change in voltage/ohms.

> 3.  Hoes does one check clearance of timing sensor ?

I don't know, but the Bentley has a section (28.18) called
"ignition timing sensor, checking". The gist of it is this:

- separate the black harness connector on the plenum

- connect an ohmmeter to terminals 1 and 2; you should
   get a reading of 1000 ohms. Terminals 1 and 2 are
   left and center when the single (center) prong on
   the connector is facing up. If 0 (no) resistance,
   replace the ignition timing sensor.

- If you see resistance, connect terminals 2 and 3,
   then connect 1 and 3. You should see infinite
   resistance. If NOT, replace the ignition timing

- If you see infinite resistance, check the wiring.

   It goes into detailed checking of the connections
   between the connector and ECU connector.

> 4.  Can I get any of these parts used at a reasonable price ?  Where?

Check the Audifans site for a list of suppliers.

> It seems that the possible probles are knock sensor, timing sensor, hall 
> sender, engine speed sensor?

Hall sender is often a problem area.  I believe if the
engine speed sensor is a problem, you car won't run.
(If I'm wrong...)


'89 200 TQ, "Bad Puppy"

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