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Discussion Starter · #1 ·
I wonder if a few people would be willing to take cold and hot measurements of their crankshaft position sensor, especially on the older, 900S and 900SE models.

That would confirm what a normal cold and hot resistance of a good sensor should be, and determine once and for all if a bad sensor can be diagnosed before it fails completely.

Mine is as follows:

p/n, from EPC: 4227203 (for Trionic ignition 1994-98)
Haynes spec: 540 +/- 55 Ohms
Measured cold: 532 Ohms (515-535 previously)
Measured hot: 680 Ohms
 

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Discussion Starter · #3 ·
BUMP! If anyone happens to have their hood open this weekend, and a meter in their hand... :cheesy: Seriously, it should not be that difficult to find a way to diagnose bad crankshaft position sensors. Not like it's the the DIC!
 

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I am getting 560 (or .560??, I don't understand ohms, just got a multimeter as well);oops:. The car was last run about 2 and a half hours ago. I will test again when hot. Am I doing this right? My meter has RX10 or RX1K range for ohms. I put it to RX1K and zeroed the needle, then tested.
 

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Discussion Starter · #5 ·
jonnyfgroove said:
I am getting 560 (or .560??, I don't understand ohms, just got a multimeter as well);oops:. The car was last run about 2 and a half hours ago. I will test again when hot. Am I doing this right? My meter has RX10 or RX1K range for ohms. I put it to RX1K and zeroed the needle, then tested.
That is correct. An ohm is a measurement of resistance. The X1K scale is in 1000's of ohms. So, 0.560x1000=560 ohms, when the engine is somewhere between cold and hot.

There is actually quite a bit you can do with an inexpensive meter on a car, b/c most of the values do not have to be measured very accurately.
 

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A lot of crank sensors will throw a bad waveform on a labscope before crapping out, too, so that might be something else to check.
 

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Discussion Starter · #7 ·
I can hook up a scope, but unfortunately I don't know what a good or bad waveform looks like in this case. I assume it has to be a certain amplitude or have a DC offset of some kind.

I was told that on start, the ecu just looks for evidence that the engine is cranking b/f it turns on the fuel pump. What bothers me is that a Saab dealer does not seem to be able to diagnose a bad crankshaft position sensor. With the Saab diagnostic tool it should be easy!

So unless there is more in the WIS, all we have is what we measure and compare.
 

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cps test

Hi, I've read a lot of info on the crankshaft position sensor on your posts and I believe this is my problem as well, I have a 96 900s 2.3 non-turbo, intermittent start problem, it cranks, starts, but no start if you try again, wait 5-10 minutes, starts and runs fine. I checked with my multimeter, it read .941 I assume this is way out of range. I wasn't sure if higher was better or worse but either way, can I safely assume that the cps is my problem? Thanks for all the great info-great site-first time user
 

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Discussion Starter · #10 ·
smoo45 said:
...can I safely assume that the cps is my problem?
Welcome to the board!

I am not sure that you can assume that. That is why I started this thread.

The multimeter may be set on the 1000 Ohm range, so 0.941x1000 would be 941 Ohms. I would verify that.

We do not know if higher resistance automatically means a bad sensor. We do know the reading is always higher with a hot engine, even with a good sensor.

I would take a cold engine measurement, and then repeat it when the engine has warmed up and the car won't start.
 

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cold check

thanks for the reply-the multimeter was set at 1000 so .941 is correct, I checked it stone cold, but I will check it again after it has run a bit. I ordered a cps anyways, it was inexpensive and if its not the problem, at least I know its been changed, I've heard its a pretty common problem, I changed the fuel pump 2 years ago, and the coil, cap, rotor, plugs, and wires this year, so that narrows it down a little-thanks for the help-I'll let you know how I make out.
 

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hot check

ok, I ran the car to operating temp and checked the CPS, it was 1.017, or 1017 ohms. I should get the sensor tomorrow FEDEX so after I install it I'll post the new readings-its a Saab sensor, not aftermarket, and I have a good ohmmeter so it should be pretty accurate.
 

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Discussion Starter · #13 ·
One more question... what sensor is on your car? The 2.0 turbo only had one between 1994 and 1998, but the 2.3L engine had two different sensors, p/n 4227203, and p/n 9177221.
 

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cps

the sensor is p/n 9177221, do you know if this sensor has a different range than those on the turbo models as far as the ohms reading?
 

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Discussion Starter · #15 ·
smoo45 said:
the sensor is p/n 9177221, do you know if this sensor has a different range than those on the turbo models as far as the ohms reading?
I don't know. My car has the other one. Perhaps we can get someone with a '96 or later 2.3L to post, or you will have to wait for the new one. One good thing, it is cheaper: #9177221 ~$39. #4227203 ~$105 :eek:
 

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to be continued...

ok, a little glitch-got my sensor but can't get the old one out, torx head is stripped. Anyone know the thread size of the screw? I will have to drill it out tomorrow (if I can find a drill to fit in that space) and get a new screw. Thanks.
 

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Discussion Starter · #17 ·
That is a tight space for a ratchet and bit holder, let alone a drill... :eek:
Article : Screw
PartNo : 7971294
Usage : M6X12
Looking in EPC, there are a couple dozen of them on the car. The most accessible "sample" one is probably at the bracket that supports the cruise control. I can check that tomorrow.
 

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cps done!

ok, its installed and car starts every time. The cold reading of the new sensor is .907 and hot is 1.027 so I didn't see a huge disparity between the readings of the new sensor and the old one.(.941 and 1.017) The non turbo models must have different resistance as this isn't consistent with the readings posted prior in this thread(.530-.670+/-)on the turbo models. Anyways, if anyone runs into the seized screw problem on the cps, I found the easiest way was to break off the old cps w/a long flat screwdriver or chisel and a hammer. This allows easy access from overhead to the screw with visegrips-heat the screw with a small flame torch and it should come out fairly easy, mine did. Thanks for all the help-hope I helped someone else.
 

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jonnyfgroove said:
O.K., the final result (these are rounded off numbers as my cheapo analog meter is kinda vague).

Cold - 540

Hot- 690
IMO, the so-called cheapo analog meter is the better of the two - and this is the opinion of the HVAC instructor, a professional.. The analog shows what is happening as well as the end result..
It stands to reason that the Hot- 690 figure is higher than the room temperature one..
And the Haynes manual should include this info......

And I do take it than the "hot" CPS is functioning perfectly ???

Just paid a quick visit to one of the "Bimmer" boards.
A disappointment , They use a screwball second rate format and they guess and throw parts at the same problems that we have.
I'd guess the BMW drivers have more disposable income than we do...
 

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Am I correct in thinking that CPS is really just a coil?

If so, then the resistance increase is just a function of the temperature coefficient of the resistivity. Few references indicate approximately 20% increase in resistance from 20*C to 90*C, which is approximately what has been observed.

How do coils fails? Either they open circuit due to extreme heat (unlikely since this is just a sensing device) or the insulation breaks down (due to heat or mechanical vibration) and causes short between the windings.
 
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