I have 2012, ML350, (about 97K miles) and I had a code P0339, crankshaft position sensor message and the car was driving in the limp mode. I replaced the sensor with a new MB Crankshaft Position sensor, cleared the code and everything was fine for about 2 weeks. Now, it came back again, the same code P0339, Crankshaft Position Sensor A Circuit Intermittent, and Cylinder 4 Misfire Detected. I believe the cylinder 4 misfire is just a consequential to the Crankshaft sensor problem. Again, the car was in the limp mode. So, I am thinking, did they sell me piece of crap sensor or is there something else going on? I bought the Crankshaft sensor on E-Bay, it did look genuine with MB logo on it, but how do I actually know where it came from? This is the 3rd crankshaft sensor in few months, but the first one was just a cheapo probably from China. Did that ever happen to you guys that you bought genuine part and it didn’t work? Or how often that happens? I am hesitant to buy another one just to find out that it is the same thing and I missed something else. I have done dozens of crankshaft sensors, but this one is an absolute ordeal! You need to remove a lot of stuf and be a contortionist to reach the damn thing. This time, I just cleared the code without replacing the sensor and the car seems fine. But I know, it may came back and if it does, I may have to buy another one. Anybody have similar experience?

 

Here is my take on your issue (I think you are coming to that conclusion as well):
1 - You initially replaced the part, thanks to the code.
2 - However, step 1 is based on the assumption the part aged and it died, BUT it could have been a consequence of something else as well, i.e. which is the root cause?
3 - You have replaced the part twice in 3 months. I think that rings a few bells: either you are getting bad parts (bad luck), or there is something damaging whatever you throw at the car . That is when "careful diagnostics comes in" or you will be in this cycle for a while until a more $$$ part is damaged.

Here is an example of what an inexpensive part can do (not the same part in your case, and not an MB but a BMW story ), and how delicate these cars are.


In this forum you will find members will help you as much as they can as long as you provide information for them to give you informed comments. The first advice you may hear is "do not buy junk parts from Ebay", along with "you get what you pay for". Sometimes the effort to replace inexpensive parts a few times will surpass buying the original part (as expensive it may initially seem).

Separately, the 2012 ML350 shares the same engine, M276, as the W212 facelifted version (2013-2016) and the forum is very active. You may want to ask there as well.

 

Do not buy junk parts from eBay. You get what you pay for.

Buy parts from the dealer.

Replace your main and auxilliary batteries.

Report back.

 

Three bad sensors is extremely improbable even if you've bought junk off of eBay. I'd look at and clean all electrical connectors with Deoxit.

 

Thanks for the info. I will report back how it goes.

 

Following @Diabolis suggestion, I would start looking at the ground near the starter, the M276 usually has one ground point on each bank as well, and there should be others around the hood, for example, one from the AC compressor to the chassis.

Perhaps @konigstiger can provide the section with all ground points for the W166. I do not have my WIS close by.

 

I learned my lesson with the eBay parts. I just bought a new sensor from the dealer. I hope that will do it. Anybody knows if this Crankshaft sensor is “Plug and Play” or do you have to do anything else in the ECU setting besides erasing the codes? I have a basic scanner I-Carsoft so, I did erase the codes and the car up and running. Keeping my fingers crossed.

 

Not exactly, but at least you got your car back on the road.

Fingers crossed it does not happen again; however, if it does , you will now have a few Crankshaft Position Sensor and probably can learn from these videos

This is about the fundamentals of the crankshaft position sensor, and how to test them with a voltmeter only


and this one is MB specific, but it only tells you how to test using an oscilloscope (not everyone has one), but worth looking at it anyways.


Now that you understood how the Crankshaft position sensor works, and how to diagnose a faulty one from a good one, you can backtrack the source of your problem. Let us take a bad case scenario, and the MB one also fails. What next? 4 bad sensors in a row for you? I am sure you do not have dark cloud following you; therefore, you may need to really diagnose the car. Since the MB sensor is 3-wired sensor, you need to verify the 3 steps mentioned in the videos.

To make it even worse, let us say you get the sensor out and it passed the 3 tests, or you have disconnected the harness and verified it is a good sensor but it is not working. That is a tough one, right? Well, guess what : your tests were intrusive and did not test the sensor in its operating environment, i.e. connected to the harness in its correct place. That is when back probing comes along (still intrusive though but less) and while you measure you move the harness around looking for a bad connector, broken wire in the harness, loose ground (as @Diabolis suggested), partially loose wire, etc and the measure will fail then..

Intermittent failures are the worst since they seem to get fixed when replace the part or you disturb their environment BUT it will settle again in the not working positions (Murphy's Law) and leave you stranded well dressed with your date while doing your best impression.

 

Plug and play.

 

The service procedures FOR MOST OTHER MERCEDES ENGINES state that a flywheel adaptation needs to be performed immediately after installing a new CPS (it basically needs to relearn where TDC is for cylinder #1). I do not know if that is also the case with the OM642 or for that matter other diesel engines and I don't have WIS nearby, but most gasoline engines require it. While the ECU should technically perform the adaptation by itself over time, keeping it below 2000-2500 rpm for the first 1,000 km or however long it would take may be a bit of challenge and obviously poses a risk.

 

I want to thank all of you for the valuable information. Unfortunately, this CSP is not easy to get to. So, back probing in this car is almost impossible due to very tight space and I can barely stick one hand down there just to reach the damn thing. That is either from the top or from the bottom. Those guys who ever worked on the car like this know what I am talking about. In order to get there I have to remove the computer, computer bracket, heat shield and another cover just for the CPS. Then you are working just a few inches from the super-hot catalytic convertor. No fun.

So, today I installed new MB crankshaft sensor from the dealer and in no time the code came back. Again, it put the car in the limp mode. However, I think it was due to the old codes. I cleared all the codes, let is set for 10 minutes, restart the car and everything looks fine. Drove around the block several times and so far, so good. As Diabolis mentioned, the flywheel adaptation is probably in order. Thanks for the info. I will have to drive it little more tomorrow. Keep you posted.

 

Well done. Lesson (re)learned - buy parts from the dealer.

 

By the way, does anybody know decent scanner for Mercedes that will not break the bank? I do have a ICarsoft II and it is OK for the basic stuff, but it doesn’t seem enough. I was looking at the Chinees laptop with Xentry software and C6 around $700. I am little worried because it is from china, but the genuine Xentry cost thousands. Also, I don’t know how difficult it is to navigate thru the Xentry. I couldn’t find any manual for that. Anybody has some experience with this? Can average Joe learn the software?

 

I got an XEntry download, and installed on an old laptop myself (i5-4th gen, 8GB RAM, 250GB SSD storage). So far so good. I cannot do coding, but I am not at that point yet, and that is good a thing to prevent me from bricking my car.

Is it better than iCarSoft (which I also have)? Definitely, night and day.

 

Message @BenzNinja

 

If you get a working XEntry system, you may want to watch this youtube channel, he uses Xentry to illustrate the diagnostic process using it. So, you can learn a few tips from him (https://www.youtube.com/@ecuboot7153...h?query=Xentry )

 

How difficult was to download and install the Xentry on your laptop? I do have Dell laptop laying around here so I could give it a good use. I like to try new stuff but coding is little tricky and I could get myself in trouble. I am with you on that.

 

It ain’t over until … There we go again. This morning I scanned the car before cold start there were no codes. Everything looks fine. Left the scanner attached, start the car, engine kind of stumbled at the beginning, then again, and then it’s running but again in the limp mode. So, I scanned it and there were the 2 dreadful codes, Crankshaft Position sensor, P0339. This is really driving me up to the wall. Now I have 3 CPS sensors, probably good ones because the problem is somewhere else. This has probably something to do with a cold start. Tomorrow I will check both batteries again. The main battery is about 1.5 years old but I will check it again. Then I want to replace the small auxiliary battery. See how it goes.

 

Sorry to hear it is back. Do not get me wrong, I know how painful it is to work in the back of the W166 engine. But, the issue must be diagnosed carefully.

If you can do the static testing of the CPS would be great. Let us be 100% certain they are OK, because they could have also been damaged by something else..

Failure analysis says to trace back one component at a time, if we jump we can be chasing a ghost upstream. In this case the sequence starts at:
1 - CPS specs are satisfied ?
2 - Connector is not damaged ?
3 - Harness upstream is working ?
etc..?

 

@mbkutil - Just to clarify something.... is your ML350 a gasoline (M276 engine) or a diesel (OM642 engine) model?

I am 99% sure that the flywheel adaptation needs to be done on the M276 following a crank sensor replacement - otherwise the ECU doesn't know when to fire the cylinder spark plug. It can roughly extrapolate the information based on the position of other sensors like the camshafts - but without an adaptation it will likely only run in "limp home" mode by design so you don't inadvertently destroy the engine.

The diesel may be different since there is no spark, but even turning the injectors on and off needs to be perfectly timed so again you may end up in "limp home" mode on it by design as well.

If you don't have Xentry DAS, I would suggest that it may be time to take it to a Mercedes dealership or an authorized service center. Your three sensors are costing you more than the two hours of labour would have if you had taken it to a shop. Let them figure it out, and then decide if you are better off having them fix it (which also carries a warranty on the repair) or if you yet again want to try fixing it yourself assuming that you have both the knowledge and the tools to do it properly. Replacing batteries and other parts at random in hopes that it may fix the problem without having any indication of what the problem actually is amounts to throwing good money after bad.

 

Diabolis that is erroneous info, please remove the post.

WIS is posted on this site, Google it. Search feature on this site is useless. I can’t attach the PDF using a mobile device.

@mbkutil please confirm which engine you have, diesel or gas.

 

Entirely possible, and if so, I stand corrected. Most engines require a flywheel calibration procedure to be carried out in Xentry following a crank position sensor replacement, but not all.

And yes, It would be helpful to know if we're talking about a diesel or a gas ML350, and I maintain that four bad sensors (including three new ones, with the last bought from a dealership) in a row is statistically next to impossible. The problem is something else.

 

Sorry, I should've mentioned it. It is gas engine with a FLEX. I was under the impression that the flywheel adaptation is done by the ECU.

 

What is FLEX???

Various minor adaptations are constantly performed by all sots of systems, but they take hundreds of hours of operating time and hundreds of kilometers covered to make a small adjustment. A flywheel relearn procedure is indicated for a number of gasoline Mercedes engines following a crank position sensor replacement, although Chassis claimed above that that may not the case with the M276 (and I don't have WIS here so can't check the procedure for the CPS replacement on that engine).

 

Flex = flex fuel for E85. Translation: gasoline engine.