Tools required:
- 8mm socket
- adjustable wrench (or O2 sensor wrench)
- tape
- jack
- jack stand
- lug nut wrench
- pre-cat sensor (online purchase $105)
- post-cat sensor (online purchase $136)
- 6-pack of favourite beer (Canadian beer is best, Americans you should buy a 24 of your pi$$-water)

Notes:
- don't bother with an O2 sensor socket, the pre-cat sensor is in a place where the socket is too big to fit.
- feed the new pre-cat sensor up from under the car, don't try to feed it down from the top, its a PITA.
- anti-seize grease is recommended on the O2 sensor threads, yet the ones I bought came with it on the threads already.

Steps:
- Drink a beer
- Open hood
- Locate pre-cat sensor on header
- Using adjustable wrench remove it and let it hang
- Drink a beer
- Jack up driver's side (you can jack up the entire front of the car, I found it unnecessary)
- Remove driver's side wheel
- Put car on jack stand, better safe than sorry! (use control or trust arm)
- Drink a beer
- Crawl under car as far as possible to passenger side
- Remove post-cat O2 sensor using same adjustable wrench
- Remove 3 8mm bolts from drivers side of second underbody panel from the front
- Remove 1 8mm bolt from same panel on passenger side (or remove all 6 and take off the panel, I only removed 4 to let it hang down)
- Locate O2 sensor plugs, both are slightly forward and above the oil drain plug on the drivers side of the engine
- Unplug both
- Tape both new O2 sensors to the plugs of the old O2 sensors (this will help you pull the new ones through as you remove the old ones)
- Get up and drink a beer
- From inside the engine bay pull the old O2 sensor out (it'll need some wiggling, the wire makes a couple turns)
- Install the new pre-cat O2 sensor, hand tighten more than snug (about 35 ft-lbs)
- From under the car repeat the same for the post-cat sensor
- Reinstall the 4 8mm bolts
- Drink a beer
- Put on wheel, remove jack stand, lower car, close hood
- You're done, drink a beer

With 2 people this took < 60 mins, having a second person to help feed the new pre-cat sensor up does help.

Sorry, no pics, this is a dirty job and I hate ruining my camera.

 

Hmm surprised nobody has replied to this thread? Well this should be the appropriate place to ask... where can I order an 02 sensor for my 2003 C230 Kompressor Sedan? I forgot the link to the online Florida mercedes parts store anyone have it or another place to get the 02 sensor for my car?

 

Nice write up..Thank you. Did you just decide to do this out of the blue or was your CEL light on?

Also same question on where to get the 02 sensor for future reference.

Thank you

 

nope my CEL has been on for like 6months now and I have to do smog now so I have to fix it. well not have to...there is always illegal smog but its about the same price as the fix so might as well fix...and get my gas mileage back

 

I know you all can't see when the DIY thread is updated so im just posting here so I can get an answer but go to this link to respond about O2 Sensors on the O2 sensor DIY topic because there is info needed in the thread that will help others in the future because the details are left out in the DIY.

https://mbworld.org/forums/c-class-w...placement.html

 

So easy a caveman could do it.
Unscrew, unplug, reverse.

 

yeah i know its gonna be easy but where can i buy it haha that is my question.

 

actually, if you just post in the DIY thread, it will show up in today's front-page listing. Yes, the DIY threads are buried in the STICKYS, but if you do post to them, they re-appear here in the general thread listings.

 

ppb - Just make sure you use genuine Bosch OE heated O2 sensors - no generics. Obviously get them at the best price. No need to go to the dealer.

 

This forum has sponsor rules, so its difficult to post where to get them from.

 

Can you PM me then. Im just trying to get this fixed so I can get my car smogged.

 

Does anyone have the part numbers for the O2 sensors? Thanks!

 

I have a 2003 with 60,000 miles on it, well ex-wife has it. Check engine light is on. I was going to buy the Bosch Universal and solder the old connector on. Or just buy it with, not sure yet. Question is this, is the pre-cat one the one that normally goes first? I have to get her to pull the codes again but am curious if that is the one that goes first, and is it the 4 wire or 5 wire variety?

 

Here's the Bosch Part number for O2 Upstream sensor before the Cat.

Part # 16272 $141.59 I just ordered one today.

 

You can also use an NTK 24321 sensor for the pre-cat. It's identical to OE. I've read that it's not a good idea to solder your own connections.

 

The O2 Sensor Downstream which is after the cat Bosch part # 16268. Plug & play.

I have checked both parts yesterday when I placed my car on the lift and both have the long wires on them. So make sure when ordering parts for w203 , order the once with 23" wires.

 

Sorry, This is the wrong part number. I have called the Bosch dealer and they replaced it for me. This part came with a very short wiring.

 

Just wondering... My CEL light has also been on for some time. Over a year in a half actually! I had replaced the MAF as well as some of the connecting tubes that hardened. The light is still on but there are times when it goes off for a day or so, sometimes longer and then there it is again. So, it's got to be the oxygen sensor I'm thinking. Now, the thing is, there is some oil on the darn connectors for all 02 sensors. I don't know if that can cause the sensors to go nutty or...? Anyway, I've removed the downstream and am letting them sit in grease removal stuff overnight. My question is this... You mentioned that your CEL light was on for some times as well. Did changing out the upstream o2 sensor do the trick? And if so, which bank? 1 or 2? My codes are calling for P0173 and P0175 which are linked to bank 2. Not only that, but if it was the upstreams you changed, how in the heck did you reach the them with that open wrench? I can barely reach it! Thanks!

 

you have a leak in your cam sensors, and possibly a vacuum hose needs to be replaced (which is on recall- free replacement) you may need to get new connectors and cam sensors. theres a thread somewhere (top of this forum i think) that talks about this

 

CLARIFICATION:

I thought I'd list out some items I learned while doing this o2 replacement this morning for anyone who wants to attempt this job. I physically completed the replacement this morning myself and must confirm a few things that have been controversial. There is no doubt about the following four items when it comes to the 2005 c230 Kompressor:

1. The correct Bosch part number for replacing the upstream o2 sensor is 17161. It's got 5 wires. Not 2 and not 4. 5 wires. See pic showing red, white, black, gray, yellow. I was surprised that the new Bosch part comes with anti-seeze already on the threads, so you don't really need another tube of it.

2. The o2 sensors cannot be replaced from the top of the engine bay. You must access it from the bottom in order to remove the plug from the car itself. This is different on the overseas right-hand drive cars, but as far as the US models are concerned, access it from the bottom.

3. If you have a Kleemann header, you do NOT need the crowfoot wrench attachment. The reangling of the 02 sensor works fine.

4. If you have a Kleemann header, the spacer between the end of the o2 sensor and the cat needs to go on the downstream one - not the upstream one. I accidentally had mine on the upstream and had to switch it after talking to Cory this morning who kindly confirmed this for me. It's also listed in one of the other threads where a member cut and pasted Cory's response to one of his questions.


TIPS ON THE REPLACEMENT:

- Tools I used: The forum won't let me attached the same photo to multiple threads, so you'll have to check out the link below for the equipment I used:
https://mbworld.org/forums/c-class-w...ml#post4520519

- You may be wondering what the telephone wire is for. I needed something to fish the old sensor out of the engine bay while keeping the same trail in order to more easily put the new one in. Use string if you have it. I don't have it, so I used telephone wire. This item is somewhat optional. I was scared that I wouldn't be able to get the new o2 sensor through the same path as the old one, so I fished it. Looking back, it's not completely necessary but helps to learn how the o2 sensor feeds through the engine bay.

- I also used an ashtray to hold the screws that I removed in order to get the two panels from the bottom of the car off. I like keeping everything together so I don't loose anything.

- The photo of everything on the ground shows the old o2 sensor on the bottom w/the new one on top. The old one has the Kleemann spacer still attached to it. Don't make the mistake I did and forget to put this back on. This goes on the downstream o2 sensor where it meets the cat. It's accessible from the bottom and you do NOT need to remove the bottom plastic panels to access this downstream o2 sensor. If you're replacing the upstream one however, you would have already removed the panels, so I guess this is irrelevant.

- In order to remove the black plug end of the o2 sensor from the car, it helps to slide both the male and female parts off the metal bracket before attempting to do so. You'll have more room. It's super duper tight and feels like it's going to break. Be careful and you'll be fine. This photo is the third one below.

- The o2 sensor is of course attached on both ends. One end goes into the cat while the other end plugs into the car. In the middle however, there are also two plastic tabs that need to be released in order to fully remove the o2 sensor from the car. The black one is accessible (barely) from the top of the engine bay (at least with my Kleemann header - not sure if how easy it is to access with the stock header, but I assume it's more difficult). The photo below shows the grey plastic tab that's visible from the bottom of the car.

- How did I fish old o2 sensor out? Connect the string (telephone wire) to the o2 sensor side of the wire. Then pull it down from the bottom after detaching the two plastic tabs. The reason you want to pull it out from the bottom vs the top (I tried that) is b/c the weird shape of the black plug part of the wire makes it difficult to pull out from the top. When I did it, it snagged on stuff. The o2 sensor side is fairly smooth and squeezes through the crevices more easily. It's not as simple as just pulling on the telephone wire though. You have to help feed it through. It would help to have a second person at this point, but it's not completely necessary. I probably hopped up and down from beneath the car to the top and back down a dozen times.

- Although I didn't replace the DOWNstream sensor, I inspected it and found that it's very accessible from the bottom of the car. The whole wire is visible w/o removing anything nor using mirrors. It's super easy. If you have another $100 to drop, you may as well replace this one too while you have everything taken apart.

- Good luck and email me if you have questions. I don't post here often, so please contact me there. I'll reply through this thread though so that everyone has all the info and can make good use of it. Good luck.


OTHER RESOURCES:

https://mbworld.org/forums/c-class-w...ml#post4520536

https://mbworld.org/forums/c-class-w...er-m271-2.html

 

thanks for the clarification... i'm about to do the install this weekend.

i purchased a sensor online, but i dont see the "17161" posted on the website. i can check the actual box tomorrow...

what was the PN of the one you purchased? was it: 003-542-73-18 ?

Thanks!

btw... i was the member who cut and paste my conversation with Cory

i've been really slow about this install since i've been driving the ML for the winter

 

ok i checked... and the Bosche 17161 corresponds to the MB Part Number 003-542-73-18

 

Casper - thanks so much for the clarification. I hate giving bum information. The RHD cars must have a different harness to LHD ones.

 

Glad you got the part number on your own. Sorry, I hadn't checked the thread until just now. Thanks for posting Cory's correspondence. It helped.

I figured. You seem like a great contributor to the forum and I hated to question you but knew there had to be a reason for the conflict. Please continue with your advice. It's much appreciated! It's great to have awesome members still active here.

 

Hello Glyn,

You've helped me on numerous occasions but I'm at my wits end with this stupid mercedes. Okay, long story short... I replaced both upstream O2 sensors because the CEL has been on for 2 years now! I first started by replacing the MAF sensor 2x, which didn't do a thing. The first time, I bought a 'non bosch' brand so had to re do it. Next, thing you should know is that there is a bit of oil leakage on the O2 sensor harnesses. After changing each one (I did them about 1 month apart), the CEL went off for about 4 or 5 days and then came back on. Questions: The oil, where is it coming from? I see it's a standard issue with the C230 but I have a C240. I replaced the CPS last year too. (crankshaft position sensor?) So I don't think the oil is coming from there, as many people said was the problem with their leak. Is it the oil leak on the O2 sensors making the CEL come on? I duct taped the sensors on the outside to stop more oil from getting on the wires before putting them in, so I don't think that's it. This website states

http://repairpal.com/OBD-II-Code-P0172-and-P0175

that the CEL could come on for reasons other than the O2 when the OBD P0172 and P0175 codes come up, which is what I'm getting. Should I take it to a place like pepboys where they can tell me what is going on with the a real diagnostic machine?

Thanks!