Richard Koop

My wife's C250 (with 100,000km) generally runs well. Except for a while I've been getting the P0340 camshaft position sensor code. Typical symptoms...

• runs great
• 50% of the time starts fine
• 50% of the time when starting cranks, sounds really bad for a few seconds (like a diesel), starts, sounds bad for a few seconds and then runs fine
• no problems when driving
• sometimes the check engine light will come on, sometimes not, sometimes it will go away on it's own

Got it diagnosed and they replaced the intake camshaft position sensor. Everything looked fine, ran great for about a week and then the symptoms and code P0340 came back.

Apparently this code points to a bad sensor or electrical connection in the harness. Should I maybe test the sensor (check ohms, check connection, etc...) and if bad replace again? Haven't checked the wiring but it looks in good shape. Can I check the connector to the sensor? If so, any idea what I should be looking for with a digital multimeter? ie. which pins are which?

Some say this could be caused by other things... Low oil, older spark plugs, battery going bad. Checked oil and it's fine. I replaced the spark plugs so they are new. Battery seems fine.

Richard

Sean_W204

Yeah I had the same problem with my C250 as well. I replaced the sensor with a genuine oem part and replaced the battery but the code would still come back and the time it took the car to start up got longer and longer with each passing day.
I took it to a European automotive specialist and they found that it was the camshaft adjuster magnet that was bad. They recommended just taking it to the dealer because the work is very intuitive. Luckily my car was under warranty at the time so I didn’t have to pay a dime when I took it in for repairs at the dealership. But based on what you described, they my unfortunately be what’s happening. The teeth on the magnet eventually wear out and the car won’t start. According to other forums I’ve seen, this happens to be a common problem with our model

ezshift5

Hi Sean,

Another C250 1.8 here.

Appreciate your input.

Sure appreciate your indicating your odometer reading when all this happened.

Thanks,


ez

Richard Koop

Thanks for the info. I'm going to let the MB dealer take a look and see what they say. If they say $2000+ charge I'm thinking I'll do it myself.


Richard

Richard Koop

No problem. Going to let the dealer diagnose the issue. We'll see.

Richard

Richard Koop

So brought the car to the Mercedes dealer in Ottawa. They diagnosed...
- minor oil leak - suggest replacing valve cover gasket
- camshaft position sensor needs replacement

Told them not to do the work. They wanted to charge me $250 CDN for the Mercedes replacement sensor.

Ordered a better quality camshaft position sensor from rockauto - Beck/Arlney.

Rock Auto Camshaft Position sensor

Before I installed it checked for oil around any of the sensors because this is apparently a known issue. Sprayed with electrical contact cleaner as well just for good measure.

Started car 10 to 15 times and never an issue. I hope the 1st replacement lower quality camshaft position sensor was the issue.

Was going to check the ECU connections for oil but couldn't find where the ECU is located. From readings I thought it would be on the top of the engine. But maybe in the 2012 C250 1.8l turbo it's somewhere else? Any help locating this would be much appreciated.

Richard

Richard Koop

Boy it's hard to find information on these cars. Here's a link to someone who replaced the camshaft phasers.

Camshaft phaser replacement

The Critic

That is me!

I still have the Baum branded timing tools from the job. If you want to purchase it, let me know.

Richard Koop

Thanks. Awesome write-up by the way!

I'm used to Honda's and Nissan's where information is plentiful and it's relatively easy to diagnose a problem.

I've done a timing belt before (actually the entire head removal and timing belt) but it was on an '81 Fiat Spider... Very different.

I just know I'm not going to pay the Mercedes dealer $4000+ for doing the job.

Anyone have any experience with the aftermarket timing belt kits?

eg. 2012 Mercedes C250 Timing Chain Kit

Richard

The Critic

The chains do wear on these engines, but at your mileage, the chain is probably still fine. Febi/Bilstein sells a tool for measuring chain wear; the measurement tool screws in place of the tensioner.



The issue with replacing the chain is that you have to “draw” the chain thru the timing case. With the engine still installed, only the upper 1/3 of the timing cover is removable. Removing the entire timing cover requires removing the lower oil pan and removing the lower oil pan requires removing the subframe. The MB method of replacing the timing chain in-car is to use a special tool which breaks the chain link (think bicycle chain) and allows you to connect the old chain and the new chain together. The crankshaft is then turned to “draw” the chain(s) thru the timing case. I was unable to find the timing chain tool for the simplex style chain used by the 1.8L turbo. However, you can supposedly use a timing chain tool set for the OM642 diesel and “make it work.”



Assuming your engine does need cam adjuster, you only need to replace both adjusters, the tensioner (one-time use), valve cover gasket and spark plug tube seals, tensioner plug, thermostat and the various o-rings. You MUST buy the M271 cam timing tool for setting the timing though.

Richard Koop

Great info again. Nice to find someone with more detail than I've found with many searches on the entire Internet!

I had oil in the spark plug wells so I was planning on removing the valve cover anyways. Then maybe I can get a much better look at the timing chain, timing tensioner and cam adjusters to determine what's required.

Richard

The Critic

Yes, removing the valve cover and setting the engine to cyl1 TDC should allow you to verify the health of your cam adjuster. Follow the pictures I posted in the other thread to compare yours. Chances are you will find a failed intake cam adjuster.

But with Xentry (and maybe Autologic), you will be able to confirm the fault codes and perform a function test of the cam adjusters without any mechanical disassembly.

Richard Koop

Thanks. I was looking at the scanner or maybe the but not sure it will give me the codes I need to test the cam adjusters. I'll take a closer look at your post but in case it doesn't answer those...

1. What do I need to turn the engine to TDC? On my Fiat I needed a big socket and a breaker bar. Is it similar on the C250?
2. How many components do I need to remove to see the state of the cam adjusters? Just the timing belt top cover and the valve cover? Or do I need to remove the alternator and other components? I think you also mention the power steering line.

And this looks pretty useful too.
Richard

The Critic

Just the valve cover. The upper timing cover only needs to be removed if you are performing replacement of the cam adjusters or the timing chain.

The reason for alternator removal is to gain access to the timing chain tensioner.

The crank bolt is a 27mm IIRC. Rotate clockwise until "0" lines up with the notch on the cover.

Richard Koop

Cool. I think I'll start with the valve cover 1st. Then I can check the camshaft adjusters and I'll probably find at least one of them is bad.

Gotta do this before something goes terribly wrong! Silly Mercedes... these cars should be bullet proof. Still have my Honda Pilot with 300,000km and the teenage beater Nissan Sentra with 290,000km! And no major issues.

Richard

The Critic

Not sure how long you plan to keep this car, but they do have other expensive issues. High Pressure Fuel Pump and Valve seats are not uncommon.

Richard Koop

Thanks. Decided to not take the valve cover off and just ordered the parts for the camshaft adjusters and the timing chain and tensioner. Done a lot of reading and this is definitely the issue. And car is getting worse.


Is the thermostat housing and drive belt necessary replacements or 'While you're in there just replace it' type of things?

And do I need a special tool to tighten the camshaft adjuster nuts? Seems like a weird socket I probably don't have.

Richard

The Critic

I would highly recommend against using any aftermarket timing components or parts with this engine.

The thermostat is supposedly notorious for breaking during removal. Belt has to come off anyway, so yes, it is one of those things.

The cam adjuster needs a T100 socket to tighten. If you purchase the Baum tools kit, it will include the socket.

Richard Koop

Thanks again. I'll check my M271 kit and I'll ordered the thermostat housing and main drive belt just in case.

Richard

Richard Koop

My M271 kit has the T100 socket. So I should be all good. Have the car for the entire weekend so hopefully things will go well. Thanks to @The Critic for the advice and help.

Richard

Richard Koop

Alright. Got all the parts. Doing the job this weekend!

So from what I can see I need to replace the timing chain tensioner as well since I have to take the tension off the chain to remove the camshaft adjusters. Or can these be removed without removing the tensioner?

If so I need to remove the accessory belt and remove the alternator to get access to the timing chain tensioner I think.

Richard

azblk

Did you timing kit come with black wedge? if it did you can use it to compress the tensioner.

Richard Koop

Ok. Thanks makes sense. So I may not have to replace the tensioner. How can you tell if the tensioner needs to be replaced? Here's a picture of the kit.


M271 kit


Do you see the wedge?

Richard

azblk

yes black block on right

Richard Koop

Valve cover removed. Still have to remove all the stuff on the front of the engine to get access to the upper timing cover.

Here's a picture of the timing chain.




Hard to tell if it's too much stretching at this point. Maybe someone can let me know what they think. One thing I did notice is that the right camshaft bolt that holds the top rail on the timing chain wasn't tight. I guess all the rattling shook it loose. Also I can wiggle that top plastic rail back and forth a bit or maybe that's normal?

Right now I'm leaning towards replacing the camshaft adjusters and the timing tensioner. But I'll know more when I get the front timing cover off and set to TDC and take a look.

Richard