[s-cars] Faulty new cps?

[Paul Gailus]

I agree with Tom's inputs about the first things to check out.

Depending on the equipment you have and your ability to probe and access
signals, you should be able to check the cam sensor operation while it's
still in the car.

Unlike the RPM or speed sensors, the camshaft position sensor
output can even be measured without the engine turning. That's because
it's a hall sensor which responds to the static magnetic field and provides
a corresponding high or low DC output level.

My understanding is that the ECU contains a pull-up resistor tied to
approximately +5 volts that is connected to the cam sensor output. 
The open-collector output of the sensor will pull this resistor voltage down to
a few tenths of a volt when the open slot of the metal vane is moved into
the sensing area.

This open slot is a relatively small portion of the camshaft  or crankshaft rotation.
See http://www.picotech.com/auto/audi.html for some waveforms from an S2
which uses a distributor containing a hall sensor.

So it should be possible to observe the cam sensor output using a scope
with the engine turning over as in this article, or by making a DC measurement
with the engine stopped. In the later case, the engine could be manually
rotated till you see if the sensor output pulls low at any position.
This should be done with the ignition on and the coils disconnected (just in case
it somehow decides to start when you don't want it to).

I'm assuming that the sensor is powered up with ignition key turned on
but without cranking. Otherwise, you could disconnect the connector to
the sensor and provide your own power & pull-up resistor to 5-12 volts
to make the measurements.

Paul

-----Original Message-----
>From: Tom Green <trgreen at comcast.net>
>Sent: Mar 30, 2006 5:33 PM
>To: s-car-list at audifans.com, dooksniffer at gmail.com, jpburns3 at gmail.com
>Subject: Re: [s-cars] Faulty new cps?
>
>Not so fast.  I think you can be almost 100% sure that engine speed  
>sensor fault
>exists simply because the engine is not running.  It will always  
>appear if you read codes
>without the engine running.
>
>The 00515 01-10 signal shorted to plus  appears to be a connector or  
>wiring problem.
>I would start by looking at the connector and wiring for breaks in  
>wiring or insulation
>between the connector and ECU.
>You omitted one piece of information - the MIL light (check engine  
>light) .  Does it come
>on when key is turned on then go out ?  Does it come on again when  
>cranking engine ?
>
>Tom '95 S6
>