I have an 89 964 C4 that throws a christmas tree lighting show and a beeper. I read the error codes using a Durametric cable and it has 2 codes:

1) O2 sensor, shorted to + or shorted to Grd
2) Knock sensor 2

Questions:

1) would those codes trigger a beeping christmas tree light show?
2) The o2 sensor is easy, but the knock sensor cables disappear under the shroud. Can I get to the knock sensor IF I take off the alternator with the engine in place?

 

You can get to the knock sensors after removing the alternator , bracket , intake and shroud , basically everything on the topside of the engine .
it certainly can be done with engine in place but time consuming ...Bert

 

Sensor input will never cause the Christmas Tree effect. High voltage sparks does. Check your coil and/or spark plug leads, and use the search function here on the forum for details.
Cheers,
Tore

 

Thanks,

Knock Sensor Installation DIY - Rennlist - Porsche Discussion Forums

I found a thread on replacing the knock sensor on a 964 where the poster removed only the alternator and the little top piece of the shroud and leaving the intake in place. That is what I was hoping for. That is a lot more manageable than removing the top of the engine. BTW, before posting this thread, I did a search on the christmas tree effect and the recommendation was to use Durametric scanning software before throwing stuff at it. The scan revealed two codes which seem unrelated to the christmas tree, hence the question.

 

The easiest way to test for damage on the high-voltage wiring is to spray water mist into engine bay while keeping an eye on the dashboard through the rear window.
In dark surroundings you will see the spark, and then the warning lights. I've done this, it is quite spectacular.
Cheers,
Tore