Replacing the Crankshaft Position Sensor on Mercedes CLK430

After my CLK430 decided to cut out without warning, it turned out to be the Crankshaft Position Sensor, as explained in my previous blog post, here. On the lead up to the random cut out, there was an intermittent rough idle and hesitation when accelerating from stationary. After the car had cut out and I let it cool down to restart it, the check engine light had also illuminated.

For this job you obviously need to get yourself a new sensor. I would highly recommend getting a Bosch sensor, don’t buy a cheap copy, it’s not worth it in the long term. Mercedes will sell you a Bosch sensor with the Mercedes-Benz name on it (see the images below for proof), so you are best off saving yourself around 50% by going to GSF Car Parts or Euro Car Parts and getting a genuine Bosch sensor. The Bosch part number is 0 261 210 170. The original Mercedes part number is A 003 153 27 28, but this has since been replaced by the part number A 003 153 28 28. It’s worth noting that the Mercedes part has the same Bosch part number on the opposite side, see below by clicking on the images to zoom in:


Once you have your replacement sensor, you can get your socket set out and get started. For this, you will need a female Torx socket (E8), your ratchet/wrench, a couple of extension bars and a universal joint. The sensor is in a fairly awkward position at the back of the engine, and the image below is to show you how I set the ratchet up to get it to work for me…


At first you will need to pull the engine cover off, which is actually really simple, and as long as you do it right, you shouldn’t break it. Firstly remove the two air intake tubes running from the front of the car to the air filter housing. You can see these in the image below. After you have removed these two tubes and put them aside, lean over the engine and put one hand at either side of the rear of the engine cover, and pull firmly in an upwards motion. You should feel the cover lift from its position. Next you need to be a little more careful as the front end of the engine cover is a bit more delicate, so hand on either side of the front of the cover, as shown below and pull gently upwards, until the cover is completely loose. You can now completely move this away from the engine bay. Place it on to something soft to ensure it is not scratched/damaged. Definitely not the concrete/tarmac floor, which I have seen some people do!

Once the engine cover is removed, you can see the lovely shiny inlet manifold (well mine is nice and shiny and new, thanks to the RAC, but yours may be a bit dirty after a few years)! Down the back right hand side of the engine is where the sensor is located, I have added a few photos to show to the location, as well as an image from Mercedes EPC to make it easier to understand.


Once you have located the Crankshaft Position Sensor, firstly remove the plug from the sensor, by squeezing the side of the clip and pulling it upwards. Using your socket bar and socket, you need to get the socket on to the bolt holding the sensor in. Awkwardly, they have placed the bolt underneath the sensor, instead of above…really helpful design there! It is a bit awkward and can take some patience, but it can be done! Once you are on the bolt with you female torx socket, undo the bolt, taking your time, ensuring you don’t slip off of the bolt head, as you don’t want to damage the bolt! Once you have began to loosen it, you may want to try undoing the rest by hand, but I couldn’t get my hand down far enough to be able to do this, so I continued with the socket bar, it takes a while, but be patient and keep one hand down on the socket itself to ensure it doesn’t slip off. Be careful not to drop the bolt down behind the engine once the bolt has been fully removed. Once you have removed the bolt, you can take a grip of the sensor and gently wiggle it whilst pulling up on it. It may be stiff as it is likely it is the original sensor from the factory, or at least been in there for a while! Just keep pulling and wiggling it until it comes out.

Now the sensor is removed, you can see above that it is a bit dirty around the hole where the sensor was…be careful if you do clean it, as you don’t want to drop any debris in to the hole, this is where the flywheel sits and debris will definitely not help things! Best waiting until you get the new sensor back in.

Get the new sensor and refit basically reversing the instructions to remove the old one. You can check they are the same side by side before putting it in. When putting the bolt back in, remember to be careful not to drop the bolt! Use a small magnet in the bottom of the socket if necessary to hold it in. Make sure it is tight, but do not overtighten, with all of the socket extension bars and the universal joint on there, it becomes easier to overtighten it, last thing you need is to strip the thread off of the bolt that holds the sensor in! That will cost you a lot of money and/or time to resolve…

Once you have done the bolt up nice and tight..but not over tight, plug the sensor plug wire on to the new sensor, replace the engine cover by placing on the top of the engine, line it up and push the front clips on first, then once it clips in at the front, push the back down until it clips in place. Replace the intake tubes, taking note of which one goes which side, they are different shapes, so it isn’t that difficult to work out. Ensure no tools are in the engine bay and start the engine. You will still have a check engine light illuminated at this stage as it is a stored fault and needs clearing. For now, we need to test if the new sensor works, so let the engine run, rev it gently a few times to see how it reacts. And then let the engine run up to full temperature, which is around 80 degrees or slightly above. This will show to if the car is going to cut out at temperature again. If it doesn’t, success!

Now to get rid of that check engine light. Although it is stored in the fault memory, if you run the car up to temperature to check it, and then turn the engine off, remove the key and then start it again and the check engine light will likely still be on…then try removing the key and starting for a third time and the light should no longer be on. The light may not be illuminated anymore, but unfortunately the fault will be stored in the memory, so this needs clearing with a diagnostic computer/device.

If the light stays illuminated, it may also need checking on a diagnostic machine, which will also allow you to turn the light off as well. You may already have a diagnostic computer to plug in. Some of the W208’s didn’t have an OBD2 connector under the dash however, like most newer models…instead, they have a 38 pin diagnostic connector to the right rear of the engine bay to the front of the black box, as seen in the photos below. Find the round cap which has an electric bolt symbol on. It has a 13mm nut molded in to it (although you can undo it by hand to be honest). Once you remove this, the connector is there. If you have an OBD2 diagnostic computer, you can buy a 38 pin to OBD2 adapter for around £7 on Amazon or eBay, I have added some photos of the adaptor that you need below, so you know what you are looking for!

If you don’t have a diagnostic computer, it may be worth investing in one for future anyway as they really aren’t all that expensive these days, some are even as low as £20 on eBay, but bear the above in mind about the 38 pin adaptor needed for some W208 models.

If you are looking for a good diagnostic computer for your Mercedes, I would highly recommend the iCarSoft MBII. It is brilliant and enables you to carry out advanced and in-depth diagnostics on most Mercedes computers, and there are sometimes hundreds! You can pick these up for around £150, but make sure you are buying from a genuine iCarSoft supplier as there are some counterfeit versions of this. If you can’t afford that one, the iCarSoft i980 is a good buy as well, not as nice to use, but does the job. It is around £85. Both come with free lifetime updates. And although both offer in-depth Mercedes and Smart specific diagnostics…they also offer diagnostics for the majority of manufacturers. Definitely worth buying if you enjoy working on your own car.

Another option is, if you are local to Farnborough, or going to a Mercedes-Benz club meet that I will be attending too, I would be more than happy to clear the check engine light for you! Just let me know if I can help.

Don’t worry about the check engine light however, obviously you will want to get it cleared as it can become annoying and you won’t know if something else goes wrong, but as I said above, the light will stay on until cleared by the three engine restarts, or cleared with a code scanner as the fault is stored in the memory.

I hope this mini guide has helped. Please let me know if you have any questions.

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