Had a tech in Vancouver B.C explain how to test your CPS, if it starts to fail. He said connect to an ohmeter, should read a steady 850-1200 ohms. using an air heat gun, start warming the sensor (not hot,but warm as it's plastic), keeping a steady ohm reading, and it should not change much. Mine started to go up fast to infinity, or just lose a reading. QWhen it cooled down, reading started.
Anyone have input for this test procedure? Also, he said if the CSP is suspect, watch the tach needle, as it should not jump when it is in the no start mode of the problem. If the tach needle jumps, it is somthing else, not the CPS. Again, anyone with knowledge about this test as well?

In the 8 years I been at my tech's MB shop, I NEVER seen a bad CPS from the older MB, such as mine; 92 to 96 S or E class but he says that in the newer car 2001 and on, it gets replaced a lot.

It sort of boggles my mind, since it's just a magnet and coil of wire, so what can go bad?? Obviously, the heat must 'melt' the wire coating causing it to open. Bottom line it must be poor quality control!

In the old manuals, the TEST for this part is JUST an ohmmeter calling for a 850 - 1200 ohms. No other test.

__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page

Well, the proper CPS arrived this morning, put it in, and has ran great all day. Nice hot weather, made about 10 starts, no more problem.
Read quite a few posts of guys going to dealers, and the shops changing everything from fuel pumps, filters, lines, modules...you name it, just to find the CPS is shot. Even the dealer I bought mine at, first thing he wanted to sell me was some ring inside the ignition for the anti-theft system,along with maybe a fuel pump, lines etc.
This is really a simple/obvious and cheap fix and I am surprised the dealers are so ignorant to the real problem.
Thanks again.

Well I took mine out again and tested it. Temp. in garage was 75 degrees F.
At that temp. CPS showed 1113 ohms and it held steady at that temp.

When I applied some heat, not to much though ohm reading increased. I stopped when it read 1200 ohms since I did not want to put on to much heat. I did not measure temp. when it read 1200 ohm. I think it's normal for resistance to increase as the temperature increases.

I'd be interested to know how many ohms a new CPS will show.

The tech in Vancouver told me it should be around 1200 ohms. Another thing was to hold it steady and give it a slight tap , and see how far it jumps around before coming back, or if it just gives no reading at all. Mine was sensitive to tapping in certain areas of the sensor, closer to the magnetic end. One time, I had to touch the tip to a metal surface, kind of resetting it to get the ohm reading back
I tried testing the wrong new one sent to me, but because it was a diffferent #, it showed about 900 ohms. The correct new one I received today was around 1200 ohms, and as you mentioned, they increase with heat. The old one increased pretty fast around 1200 ohms,went up and up and then just crapped out until it cooled off a little, then read it again, crapped out as soon as the heat was put to it. The new one didn't increase dramatically when heated, just slowly went up. I never heated it much, but it seemed a bit more steady paced, when the old one just bounced right off the scale pretty fast. I am thinking maybe , especially on a warmer/hot day, the increase in temp around the sensor would cause the unit to fail faster, cut in and out more often, longer cool down time as compared to a colder, rainy day, when maybe it wouldn't even crap out at all? Just a thought, since we're dealing with a coil, or wire expanding with heat. I know on our snowmobiles, the CDI unit would do the same when failing, die when hot, reconnect inside and work again when cold, and eventually just die out completely. Tomorrow, I will take it on a drive, 120 km to another city, and back. I will post again what happens, if anything new, as it will be warm out again as well.

Drove about 250km today, nice hot day 26C. I made about 10 starts as well and everything seems fine, never missed a beat. Will keep you posted if anything happens.

I got around to getting a new CPS. It came a Hella box with MB part number on the box of 003-153-2828, I believe that is the correct number. The sensor itself has the number and manufactorname ground off, it only says made in Germany.

I test the new one with an ohm meter and it measured 664 ohm applied heat with heat gun and it slowly went to 725 ohm.

When I tested my old one it measured 1148 ohm applied heat and it quickly went to 1250 ohm.

Are the ohm readings supposed to be different for the new CPS?