[Benzyle]

I have now had to replace the crankshaft position sensor on both of my CLK320's .
In each case the sensor failed when the car became 13 years old,regardless of the mileage. One car had only done 40,000km or 24,000 miles,but it still failed.
So my recommendation is,if you have one of these cars and have not replaced the sensor after 12 years,just do it.
That way you may avoid being broken down,needing a tow,at what will almost certainly be a most inconvenient time.:wink

 

[keyhole]

^^^ +1 on that advice.

That is exactly what happened to me earlier this year when my car was precisely 13 years old!

For some time I had been thinking that I should carry a new CPS in the car in case mine suddenly failed miles from home. When it happened, fortunately I was close to home, but I then discovered that on my M112 engine access is almost impossible. It was totally out of sight and had to be removed by 'feel'.

It's much easier on the M113 engine, which is on the WIS drawing shown below.

Note - I don't remember that my CPU needed 'initializing'.

 

[rudeney]

I used to carry a spare in the ML, but then I realized it was unlikely that I'd replace it on a hot engine by the side of the road. Instead, I'd have it towed back home or to a safe place and let the engine cool down before doing the job.

Also, I am not sure why WIS says to code the ECU. I can't imagine how it could need anything as it's a binary signal activated by the fixed openings on the flex plate.

 

[Benzyle]

Thanks Keyhole and Rodney.
Mine failed when I was out of town(just my luck),so I had to get a mechanic to fix them. It does not look to be what I would call an easy job as you say,very limited access,even if you do remove the maf/intake pipe,which I have never done before.
Pretty sure all they did was clear the code,,,the Check Engine Light was on.
Amazing how a part can fail due to time or age,and not usage.

 

[thrilos81]

Mine was failing on and off when I was taking a trip down to San Diego. It made it all the way through back to San Francisco and I did the change myself. It is frustrating doing it for the first (and hopefully last) time since you are doing it by feel as mentioned. It is literally out of sight on the transmission bell housing. A long magnet wand is a necessary tool

 

[amusa]

Really, My CLK500 is a 2004. I bought it in 2006 and I still own it till this day and I have replace the crankshaft sensor twice already (60-70miles each time). The first time I got no CEL and had to call a tow truck but the second one I got a CEL and I was on my way to the shop for service A or B so they pulled the code and I decided to leave the car there over night.

 

[93SoCal400E]

This is an interesting observation on the 12-13 years thing.

I just did another thread a week ago about how I replaced the CPS on my 2005 CLK500. Car has just under 30K miles, definitely not a "high usage" item, but right between 12-13 years old.

 

[Benzyle]

This is an interesting observation on the 12-13 years thing.

I just did another thread a week ago about how I replaced the CPS on my 2005 CLK500. Car has just under 30K miles, definitely not a "high usage" item, but right between 12-13 years old.

Thankyou SoCal.
It seems they have a life of 12 to 13 years,,,regardless of usage.
If anyone else has experience or observations of when their CPS died it would be good to get more cases to prove or disprove this theory.
Specifically,age and mileage.

 

[rudeney]

I don't believe age and/or miles is the determining factor in CPS failure. My C240 is over 16 years old with 170K+ miles, with the original CPS, and there are plenty of cars under 5 years old that have them fail. This is also not an MBZ problem - it affects almost all makes and models - just search The Internet and see.

So, what makes the CPS fail? You can search that, too, and find many answers. The CPS uses a Hall Effect sensor which generates a small electrical charge when it is exposed to a magnetic field. It sits above the flywheel (a.k.a. flexplate) detects its rotation. The outer rim of the flywheel has perforations of "teeth" and "gaps":

As a tooth on the flywheel passes under the CPS, the Hall Effect sensor detects a change in the magnetic field and sends a signal to the ECU. I am fairly certain that the flywheel itself is not magnetic, but instead, there is a magnet on the end of the CPS with a Hall Effect sensor above that. When a tooth passes under the magnet, its magnetic field changes and that is detected. This is a very simple, proven piece of solid state electronics. It has no moving parts and is not subject to any wear and tear. However it is exposed to extreme temperatures, and that is when it seems most likely to fail.

The magnet in the end of the CPS has to sit very close to the teeth on the flywheel in order to get a pulse, within about 0.75mm. I believe that temperature-related failures are due to very small deformations of the bell housing, flywheel or even the CPS itself causing the gap to expand enough so that the magnetic field is too weak for a proper pulse. Another possibility is that temperature changes may deform the semiconductor material inside the CPS. Once the temperature equalizes, such as by pouring cold water on a hot sensor/bell housing, it works again. Slight variations in bell housing shape, CPS length or flywheel shape can make some cars or CPS more prone to these intermittent failures.

Of course some CPS's fail totally. This could be due to enough hot/cold cycles that permanently deform or damage the sensor, its internal wiring breaking, or even metal particulate from the flywheel collecting on the magnet on the end of the CPS.

So, why do "cheap" or "fake" CPSs fail? I would guess because they are simply not made to the exacting tolerances of an OE or genuine Bosch part. This makes them more susceptible to changes in temperature.

Well, that's my "how to build a clock" post for the day (I think!).

 

[Marsden]

Awesome contribution Rude Boy! Thanks very much.

 

[KerryM]

My CPS failed at 15 years old, at 70k miles on my CLK320, I agree with the above comments, one of the trickiest jobs I've ever done on a car! What should be a 10 minute job, due to access (as has been said, unable to see it, and only just able to feel it), probably took about 3 hours, especially retrieving the screw when it fell onto the undertrays more than once!

 

[Benzyle]

Well done ,,my tip is to secure the bolt to the cps using blue tac before you put the CPS into position.

 

[KerryM]

Well done ,,my tip is to secure the bolt either to the cps , or to your socket using blue tac so it won't fall.

Hi Benzyle, yes, I did that too, used some 'plumber's mait' which is a similar consistency to blue tac, and I still managed to knock the bolt out of the socket a few times! The relief when the bolt went into the hole and tightened up, very satisfying! Made me forget my cut and bruised hands!

 

[lgc]

I don't believe age and/or miles is the determining factor in CPS failure. My C240 is over 16 years old with 170K+ miles, with the original CPS, and there are plenty of cars under 5 years old that have them fail. This is also not an MBZ problem - it affects almost all makes and models - just search The Internet and see.

So, what makes the CPS fail? You can search that, too, and find many answers. The CPS uses a Hall Effect sensor which generates a small electrical charge when it is exposed to a magnetic field. It sits above the flywheel (a.k.a. flexplate) detects its rotation. The outer rim of the flywheel has perforations of "teeth" and "gaps":

As a tooth on the flywheel passes under the CPS, the Hall Effect sensor detects a change in the magnetic field and sends a signal to the ECU. I am fairly certain that the flywheel itself is not magnetic, but instead, there is a magnet on the end of the CPS with a Hall Effect sensor above that. When a tooth passes under the magnet, its magnetic field changes and that is detected. This is a very simple, proven piece of solid state electronics. It has no moving parts and is not subject to any wear and tear. However it is exposed to extreme temperatures, and that is when it seems most likely to fail.

The magnet in the end of the CPS has to sit very close to the teeth on the flywheel in order to get a pulse, within about 0.75mm. I believe that temperature-related failures are due to very small deformations of the bell housing, flywheel or even the CPS itself causing the gap to expand enough so that the magnetic field is too weak for a proper pulse. Another possibility is that temperature changes may deform the semiconductor material inside the CPS. Once the temperature equalizes, such as by pouring cold water on a hot sensor/bell housing, it works again. Slight variations in bell housing shape, CPS length or flywheel shape can make some cars or CPS more prone to these intermittent failures.

Of course some CPS's fail totally. This could be due to enough hot/cold cycles that permanently deform or damage the sensor, its internal wiring breaking, or even metal particulate from the flywheel collecting on the magnet on the end of the CPS.

So, why do "cheap" or "fake" CPSs fail? I would guess because they are simply not made to the exacting tolerances of an OE or genuine Bosch part. This makes them more susceptible to changes in temperature.

Well, that's my "how to build a clock" post for the day (I think!).

My 2004 CLK500 Convertible with 83000 miles turned over but wouldn't start when hot. Started again after about 25 minutes. Check engine light came on and code thrown was PO 335. I replaced the CPS with Bosch OEM part. If my hands were any bigger I don't think I could have done it. Car started up, engine light went off and it ran great for a few test runs and then the no start happened again on a hot day after a 10 mile run and then sitting for about 1.5 hours. Started again after about 10 minutes. I reset the ECU and thought that had solved the problem as it ran great for several short test runs and a 10 mile one and then sitting for 2 hours. Drove 10 miles home and let it sit for about 30 minutes and to my extreme disappointment it turned over strong but wouldn't fire up. After about 30 minutes it started up fine again, but check engine light is on.

Is there any chance the Camshaft Position Sensor could be the problem even though PO 335 code came up?
If the problem is warpage of the bell housing or flywheel what would the fix be?

Any ideas where I should go from here. A big thanks to anyone who may be able to help

 

[rudeney]

No, that is only indicative of a bad crankshaft position sensor. Where did you buy the part? If from eBay or Amazon, there is a very high chance that it is fake - cheap Chinese garbage disguised as "Bosch".

 

[Benzyle]

You could try doing a CPS adaptation after a reset or battery disconnection for half an hour...
but if you do have a counterfeit part as Rodney suggests , it will not solve the problem.

 

[lgc]

No, that is only indicative of a bad crankshaft position sensor. Where did you buy the part? If from eBay or Amazon, there is a very high chance that it is fake - cheap Chinese garbage disguised as "Bosch".

Thanks Rudeney for the quick reply. You may be on to something. I did order the part from Amazon. Would you trust Rock Auto or put them in the same category as Amazon. Mercedes dealer may be the safest bet. Any other suggestions.

 

[Benzyle]

fcpeuro.com
Only sell genuine parts ,,good service and warranty.

 

[lgc]

You could try doing a CPS adaptation after a reset or battery disconnection for half an hour...
but if you do have a counterfeit part as Rodney suggests , it will not solve the problem.

Thanks Benzyle for the help. I did have an independent shop index the Crankshaft PS to the Camshaft PS and I did disconnect the battery for a half hour. Sounding more like a fake CPS.

 

[lgc]

fcpeuro.com
Only sell genuine parts ,,good service and warranty.

Fcpeuro have an OE Bosch CPS's.....0031532728--$25.89 and genuine mercedes 0031532828--$145.66. I'm stumped as to why there is such a difference in price. I am in Canada so shipping from US during covid has gotten expensive and time consuming.