UrS4 Frequently Asked Questions

The Cam Position Sensor is used by the ECU (Engine Control Unit, i.e. the Motronic Computer) to figure out where the pistons are early in the starting cycle rather than waiting for the G4 crank position sensor to come around. If the ECU does not get a cam position sensor signal, it will not fire the J17 fuel pump relay. Once the engine is running, the ECU will use the G4 crank sensor position sensor to keep track of things. If the cam sensor fails, a “2113″ blink code will be thrown (into memory) and check engine light will come on. If it fails while running, you can keep driving but as soon as you turn the engine off, you are done. The engine will NOT re-fire until you fix the cam sensor. You might get lucky once or twice by cooling the cam sender down (try poring water down the back of the cam belt cover) Location photo and diagrams in the URL links below.

Marc S. recently (March 09) added:
“that if your CPS has failed (or is on the way out) and you need a way to drive the car disconnect the 3 pin connector at the CPS (front of the fuel rail) and shove a piece of wire or a paperclip or whatever between pins 2 and 3 (you can read the pin numbers by pulling back the rubber boot) on the car-harness end, leaving the sensor itself disconnected.

I had posted about this earlier but mistakenly suggested that you hold the signal pin up at 5v (pin 1), but in fact it needs to be held to ground (pin 3). Just came across this with a customer and thought I’d share / correct my early post.

Note: by doing this you have a 50% chance of starting the car. If it doesn’t start right up, stop, try again. repeat. Probability has it that you’ll get it fired up after 3 or 4 tries max, but I suppose it depends on how unlucky you are ”

This might come in handy sometime.

Cam Position Sensor (G40 “Hall Sender”) location diagram (EDITED)

For those that were afraid to ask. (Its behind the exhaust cam sprocket). The sprocket has to come off to get at the CPS. And the belt has to come off the sprocket (or be zap strapped to it), etc.

Definitely a good part to replace IF it hasn’t failed and you are due for a second timing belt replacement.

To replace this expensive little begger, you need to find it at the least cost. Then you need to take as many things off the front of the engine as required to get at the cam belt cover and the tensioner. If you are clever, you can zap-strap the belt to the cam pulley and keep the tension on it slightly so you can a) slide the cam sprocket and the belt off the exhaust cam as one unit and b) avoid having to totally replace the cam belt (which is a good idea if its almost due anyway). Be aware that the cam sprocket has a cast “key” and if you brutalize it with something like an air rachet, you might just snap the key off the sprocket – then you are looking at a new sprocket and probably a belt replacment – unless you suddenly get clever again.

Today, my friend and I finally finished the TB and also replacement of the CPS hall sender (BB automation sender). The CPS was the culprit why the car was not starting. The TB was routine maintainence since I had the car apart anyway. Along with the TB, I replaced both PS hoses (rebuilt by Pirtek), and added Samco hoses. Total work time for both days was probably close to 8 hrs. All in all, a very rewarding experience once the car started.

For the TB, I used the write-up from S-Cars and SJMautotechnik. The biggest pain was of course the crank bolt. After looking at the suggestions from the members here yesterday, I opted to us the pry bar method (I didn’t realize the Audi 3256 tool was $160!). It finally came loose. Next time, I will just get the TB tools from Blau. I’m sure it’ll be much easier. For those of you who have bought the CPS sender from the GB, the easiest method to install it is to first drill out the rivets from the old sender to get it out of the bracket. The new sender is a direct fit and you will have to flare out the rivets (use a punch, awe or an oversized nail) to make it hold onto the bracket. It’s a perfect fit. That is the way the old sender was secured onto the bracket.

Thanks to all for your contribution to this forum. Without you, I wouldn’t have been able to pull of this procedure.

This is a good one. Lots of details and photos.

A real keeper

My story:

To remove t-belt plastic cover you have to
remove ribbed belt rensioner. Then just
unscrew airduct and wiggle it a little bit
to have more room for camshaft sprocket screw.
I was unable to remove it completely, I wonder
how author of previous procedure did this.

Machining 23mm socket to be much smaller
(sprocket screw needs only 5-6mm deep socket)
helps a lot.

Unscrew all of the spark plugs and both CKP and RPM
sensors. Using 23mm socket with extension
turn crank to match upper (camshaft sprocket)
and lower (belt pulley, lower guard) timing
marks, checking for 0 mark on flywheel is not
necessary, some of you may even not have it at all.

Now with screwdiver inserted through opening
where normally CKP and RPM sensors are, block
crank and loose sprocket screw.

Mark rib on timing belt where is upper timing
mark and take sprocket with belt off, you don’t
have to tension it at all times, in fact
sprocket alone will be helpful later.
http://i13.photobucket.com/albums/a258/maciu/Audi/C4%20S4/Motronic%20And%20Sensors/CPS%20-%20Hall%20Sender/DSC07567.jpg

But at first I did secure belt to sprocket
and tension the whole thing.</a>
It is not necessary.

Then unscrew CPS bracket, plastic trim screw,
and gently remove CPS (mine bracket didn’t break).

Do all the necessary work (soldering, cleaning
etc.) with new CPS.
http://i13.photobucket.com/albums/a258/maciu/Audi/C4%20S4/Motronic%20And%20Sensors/CPS%20-%20Hall%20Sender/DSC07572.jpg This is the result.
As you can see I’ve used RPM sensor plug.

I have also cleaned the whole place with brake
cleaner. You shouldn’t worry about t-belt
because all of the cleaner will drip behind
plastic cover besides it vaporizes quickly.
Before. After.

Now reinstalling everything:

Put t-belt on the sprocket and try to install
it on camshaft. You may not be able to tension
belt enough to snap it on easily.
Using sprocket alone I tried different camshaft
positions (very small movements actually) and
I’ve found perfect one – almost no tension was
required to put sprocket back on cam.
Everyone should be able to do it if
timing belt is not overtensioned.

Now put some locking compound on sprocket screw
and again block crank, tighten screw.

Later I turn crank using upper cam screw few
times checking timing marks and everything
was perfect.

The rest is just reverse.

Maybe it’s not the prefect procedure but it has
at least two advantages over the previous one:

- you don’t need any swearing friends to help you
- gives you yet another occasion to make sure
your spark plugs are properly torqued

It’s good to replace ribbed belt tensioner
screws at that time or at least use some anti-seize
for them, mine were rusty and I had some problems
unscrewing them.

Hope it will help someone, someday.

All pics

By Jonathon in Ontario at my suggestion after he was able to replace the CPS without completely removing the timing belt (TB)

well I had big help from some of the guys here on the forums..I was asked to do a write up on how to change the cam sensor without having to do the timing belt removal..

very easy do to:

first off
remove plastic cover of timing belt..
remove the air ducting that goes from the front of car to the airbox area….why you ask I will tell you… If you try to remove the cam spocket bolt with a wrench you dont get a good grip on it becuase of the tight area..by removing the air duct you can get a socket and extension and get good force on it..
now after the bolt is off there is a little 10mm bolt that holds the plastic by the spocket that the wiring of the cps goes under… you want to remove the bolt to be able to remove the wiring and also for installing the new one.
Next with a friend remove the sprocket and have a friend keep tension on it so the belt does not move…you may need a rubber hammer to get it off the cam…now while your friend is swearing at you to hurry up lol… remove the 2 5mm allen bolts holding the cps…I found it really tight, use a flat head screw driver to pry it off if you have to…mine broke when I did it but who cares in the garbage it goes…
..so to re install I used some antisieze on the cps bolts put it in the same way..tighten down the bolts..and run the wiring back the same way and the end of the wiring clips to the fuel rail area…now that its installed tighen up the 10mm bold that keep the plastic tight by the wiring…slip on the cam spocket tighten it up..add the plactic timing cover and air duct and done… mine started up right away and check engine light is not on… if I was to do it again I bet I can do it in 10min…
Ps i didnt have the torque specs on the bolts if someone has please post them

I think I got it all..if something is not clear post up I will reply…sorry I dont have pics guys right now its all together so that would not help

Courtesy of Nate P. (ImQuattro)

• Click Here
  

The Cam Position Sensor is used by the ECU (Engine Control Unit, i.e. the Motronic Computer) to figure out where the pistons are early in the starting cycle rather than waiting for the crank position sensor to come around. If the ECU does not get a cam position sensor signal, it will not fire the fuel pump relay. Once the engine is running, the ECU will use the crank sensor position sensor to keep track of things. If the cam sensor fails, a “2113″ blink code will be thrown (into memory) and check engine light will come on. If it fails while running, you can keep driving but as soon as you turn the engine off, you are done. The engine will NOT re-fire until you fix the cam sensor. Location photo and diagrams in the URL links below.