Camshaft Hall effect switch works in other Audis except mine!!!???

Nate Stuart nathan.stuart at
Wed Sep 6 23:36:04 EDT 2000

If the wiring is good, and there is power to the sensor, then perhaps it is
the actual sensor pickup inside the ECU that is bad. Try swapping the ECU's
and see what happens. Perhaps the ECU is feeding back voltage to the other
side of the switch as well, and that is why they cannot get a fluctuating
voltage on their scope.

'86 4kcs(soon to be t)q
'87 5kcstq (donor, need parts!?)

> We now know where the problem with the '94 100S that will not start...when
> the camshaft Hall effect switch is taken from a running Audi and placed in
> 100S, the switch will not work as checked at the switch itself (wiring to
> ECU is good).
> Place the Hall effect switch back in the running Audi, the switch works
> as evidenced by the generation of variable voltage...and a running car.
> Disable the switch in the running car, and the same symptoms show up, the
> will not start/no error codes are generated (the word is that the car must
> running for the error codes to be generated.)
> The Hall effect switch is triggered by a piece of metal on the
> trigger is still there and visible.
> Anyone hear of such a problem?
> I am told that nearly every Audi expert within 100 miles is stumped by
> one.
> Chris W.
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