DIY: M271 O2 sensor replacement
05-26-2013, 02:21 AM
#26
This morning I performed an o2 sensor replacement after getting codes p0131 and p0171 (thats sensor 1 low voltage and bank 1 running lean). I actually cleaned my MAF first to see if that would smooth out my rough idle, but nada. It also didn't relieve the error codes. So I replaced sensor 1 on bank 1 (pre-cat, passenger side, US) according to my codes.
I wish it was as simple as that, but I'm still getting a slightly rough idle. I've read that the p0171 code could mean various things OTHER than a bad o2 sensor. Possibly a vacuum leak?
Has anyone had any experience replacing their o2 sensors only to find that there was a different problem causing a rough idle?
Please not I have no power loss issues. The car is just vibrating more than normal when stopped at an idle.
I wish it was as simple as that, but I'm still getting a slightly rough idle. I've read that the p0171 code could mean various things OTHER than a bad o2 sensor. Possibly a vacuum leak?
Has anyone had any experience replacing their o2 sensors only to find that there was a different problem causing a rough idle?
Please not I have no power loss issues. The car is just vibrating more than normal when stopped at an idle.
08-15-2013, 10:24 PM
#27
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2019 C300 Wagon; '75 Triumph TR6; previous: 2004 C230 6spd sold after 17 years of driving
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:
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.
TIPS ON THE REPLACEMENT:
- 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.
- 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.
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:
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.
TIPS ON THE REPLACEMENT:
- 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.
- 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.
followed the these instruction and worked like a charm, took about an hour from start to finish, not a hard job just fiddly and like he said I to must have got from under the car to top at least a dozen times, it really helps to have an helper to pull the new O2 sensor while you guide it up.
I used a 7/8" open end wrench and a 7/8" mini open end wrench. Thread in the O2 sensor first and then untwist the wire clockwise before plugging it in. I used a stiff piece of copper house wire tapped to the new O2 as my lead to fish the O2 back in.
Went with an OEM from http://www.oediscountparts.com/partl...?siteid=215242 $201 all in and picked it up from a friend in Buffalo, sure beats the $503 + 13% tax that MB Canada charges for the same part...we get so overcharged on parts here
Last edited by Boom vang; 08-15-2013 at 10:30 PM.
11-18-2013, 02:54 PM
#28
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E350
Hey Scottyballz,
I like your DIY on the replacement of the O2 sensor.
Are these steps just for the C Class? I have a 2006 E350 and I cannot find my O2 sensors. Can some guide or send pix for the locations. I need to find the upstream and downstream for both bank.
Anyone that has an answer of picture let me know please.
Cheers.
I like your DIY on the replacement of the O2 sensor.
Are these steps just for the C Class? I have a 2006 E350 and I cannot find my O2 sensors. Can some guide or send pix for the locations. I need to find the upstream and downstream for both bank.
Anyone that has an answer of picture let me know please.
Cheers.
10-22-2016, 04:49 AM
#29
MBWorld Fanatic!
Did both sensors today. Got genuine Bosch from Rock Auto for ~$200 total. One thing that wasn't clear to me (maybe I missed it) was that the connectors for both sensors are right next to each other and are located on the driver's side underneath the car. From this perspective it makes sense to replace both at once. I jacked up the front of the car and put it on jack stands. I removed both under trays but you could probably get away with only removing the front one. Definitely get some string as Casper suggests and remove the front sensor from the top. The clips on the front (upstream) sensor are a bit of a pain to deal with, especially the one closest to the sensor which is behind a bunch of tubing. Start to finish was ~hour indeed. I'm hoping the car will get better gas milage (106K+ miles) but mainly replaced because I've been waiting for the 'HTR' (i.e. O2 sensor heater) to finish its emission cycle for a long time now... I need to go back and read Scottyballz original post - it was a 4 Leinenkugel job for me, but I was drinking the last of my summer shandy's which go down way too easy. 
Last edited by mtnman82; 10-22-2016 at 04:19 PM.
02-01-2023, 11:46 AM
#30
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Mercedes benc w203 c220 cdi
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.
- 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.
