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Discussion Starter #1
I can understand a leaky seal, cracked hose, a worn cam,

but when the CPS aka Crank Position Sensor breaks down,

what actually physically or electrically happens?

Seems such a simple part?????????
 

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Old age, high mileage, heat, cold and other conditions will the cause the sensor to die ultimately just like any other engine electrical part.

The sensor is basically dead when the resistance value goes to high causing a no start or stall out condition. Similar to how the outside temp sensor dies for no apparent reason.
 

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Discussion Starter #3
I appreciate that it may indeed seem as if "for no apparent reason" when nothing is visible to the naked eye, but I tend to think that there still might be an explanation based on some laws of mechanics, chemistry or physics.
 

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Same way an ABS sensor fails, it's just a magnet and electrical wiring.

They fail when the resistance values change.

Why do plug wires start leaking voltage past the silicone sleave
and start arcing?
 

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there still might be an explanation based on some laws of mechanics, chemistry or physics.
Here are the explanations:
Chemistry-matters change when heated.
Physics-when matter is heated its physical/molecular structure changes.
Mechanical-When cps' physical structure change it can't obtain the needed information to send to the main ECU.

I'm not a Chemist, Physicist nor a Mechanical Engr., these are just my wild guess.:D
 

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Discussion Starter #6
as a guitar player I am used to my pickups also being magnets and coils and never ever do they fail.

I am not questioning the fact that they do fail, I know they do.
But the reasons have been vague.

What should the manufacturer for instance do to lessen the failure rate
I just wanna understand what happens electrically.
I can understand a bulb going coz the filament breaks, or sheathing rotting away, but with the CPS does the magnet weaken?
Do the coils inside break?
Has no one compared an old one with a new one?
 

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It's the wiring that's the problem more than anything else when it comes to the CPS.

As stated, it is subjected to vibration, heat, cold, oil leaks, etc.

Given sufficient time, the copper strands just change ever so slightly, along with the fact that the copper wire itself may have slight impurities such as trapped oxygen cells and hairline fractures. This ultimately cultimates to the point whereby the wires themselves can no longer carry the proper electrical signals back to the ECU which controls the engine.

In case of the CPS, the ECU can no longer determine the proper position of the crankshaft and as a result you have a no start condition.
 

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as a guitar player I am used to my pickups also being magnets and coils and never ever do they fail.

I am not questioning the fact that they do fail, I know they do.
But the reasons have been vague.

What should the manufacturer for instance do to lessen the failure rate
I just wanna understand what happens electrically.
I can understand a bulb going coz the filament breaks, or sheathing rotting away, but with the CPS does the magnet weaken?
Do the coils inside break?
Has no one compared an old one with a new one?
Actually guitar pickups, yours included, do act the same way. The difference is that you have the addition of an amplifier that prepares the signal to the level you want it at.

With a CPS, they get to a point where the voltage they generate is no longer tolerable by the ECU - the computer doesn't "recognize" the signal as being the value it is programmed to "see". If the CPS circuit had a volume knob on our dashboard, we could squeek out a few more miles from one that is dying, by "turning up the volume" on the signal. Eventually we will get to the point where it totally fails. The problem is that if we had knobs on the dash for all the sensor's whose values change over time, we wouldn't be driving any more - we'd be busy making adjustments :)
 

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Discussion Starter #9
Ok, I read you: The manufacturer originally put in crappy wiring that oxidizes away helped by heat. Mine actually failed showing only 3 ohms resistance, almost a short circuit.
 

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Ok, I read you: The manufacturer originally put in crappy wiring that oxidizes away helped by heat. Mine actually failed showing only 3 ohms resistance, almost a short circuit.
I'd tend to imagine that 2 decades of heat and cold cycles tends to disagree with crappy wiring. It's lasted that long in harsh conditions, I would tend to think that the wiring is rather durable.
 

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If you stuck your pickups to an engine, with extreme cycling heat, oil, water and vibration plus variable Voltage they might fail after 15 or twenty years....?




If you really want to know why solid state electronics fail, you have some interesting reading ahead!
cheers!
 

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1) the wire wrapped around the iron core of a sensor is very, very fine (finer than a human hair) and coated with a very thin layer of paintlike insulation.

2) the sensor element is molded inside a hard plastic shell/housing

3) the sensor is mounted right to the block and it goes through extreme temperature cycles; like sub-zero in the winter to (I'm guessing here) 200+ degrees in the summer, especially during the "heat soak" that occurs after engine shutdown.

Take many, many turns of hairlike wire wrapped tightly around a core and then heat/cool the thing thousands of times. Eventually the wire insulation will crack or chafe and adjacent wires will touch (short out). Or the wire will break. It's done...
 

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as a guitar player I am used to my pickups also being magnets and coils and never ever do they fail.
If you stuck your pickups to an engine, with extreme cycling heat, oil, water and vibration plus variable Voltage they might fail after 15 or twenty years....?
1st thing I thought of when I read the guiter analogy, where's the heat
cycles and weather on the guiter??:rolleyes:
 

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Old age, high mileage, heat, cold and other conditions ...
..and oil leaks.

Yup..sounds like me.

trauha, when you get to my age you'll find out in person why these things fail. When the only hair on your head grows out your nose and ears and and the "ECU" voltage goes haywire and maybe need a pacemaker like me:p.

Lots of other analogies here too...
 

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Discussion Starter #15
augapfel - thanks!
Your answer describes best in detail WHAT breaks, that satisfied my curiosity the best! I have seen the sensor only on sale - I guess some just keep the original leads and the plug end, and just swap the sensor, saving money.

I also appreciate the analogies from you others of how everything fails with time.

A bulb going out almost annually does not surprise anyone, maybe coz they are easier to change. Some of the wiring never craps out - anyone need to change a starter motor lead for instance?

I guess the parts are designed for differing life cycles, and Mercedes in their wisdom makes the short lived ones the easiest to change. (except for the gear shift position light on a W140 haha!!)
 

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My CPS shows 3 ohms and my car won't start, that is a REAL problem for me. Understanding how and where it is broken would give me a solution. Identifying which of the parts : sensor, wire or plug to change gives me a strategy. I apologize that you felt that answering this problem was a waste of your resources.
 

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My CPS shows 3 ohms and my car won't start, that is a REAL problem for me. Understanding how and where it is broken would give me a solution. Identifying which of the parts : sensor, wire or plug to change gives me a strategy. I apologize that you felt that answering this problem was a waste of your resources.
You didn't waste anybodies time or resources. The thing just got old and wore out and you just asked a question which was fair enough.

When mine broke I just assumed the wire got brittle and tired - like me.

But I didn't know it was broke until I asked the question why my car just stopped dead.

Ask away!:thumbsup:
 
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