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This is my first post. I own a 2013 ML350 BlueTec with 46,000 miles. Check engine light (CEL) came on and I checked the ECU codes with a scanner. A permanent P2201 code was displayed which appears to correlate to a bad front NOx sensor. I contacted the nearby Benz dealer and they estimate between $1k and $2k to repair the vehicle. I'd like to replace the sensor(s) myself if possible to save a few bucks.
Based on what other folks have posted it seems a good idea to replace both NOx sensors, front and rear. Part numbers are Front = 0009053503 and Rear = 0009053603, though I noted there is discussion that these part numbers have been replaced or superseded by a later part version.
I have been unable to locate any online diagrams or figures depicting the location of the two NOx sensors. Today I took a photo of the underside of my Benz in order to identify the two NOx sensors (See Photo). I believe #2 is the rear NOx sensor. I'm not sure of numbers #1 and #3.. #1 might be the DEF injector. I couldn't find the location of the front NOx sensor so any help would be appreciated. Also it appears a few under body panels will need to be removed to access the NOx sensor control units, but again I'm just speculating. .
2013 ML350 Bluetec, 1966 Ford Mustang Convertible (sold)
My brother in law is fighting the same issues at the moment. He was getting P29F and P2201. He changed both NOx sensors and cleared the codes, but they came back. He then went to an indy shop and they adapted/learned the NOx sensors to the SUV and cleared the codes. Well, the codes came back again...
Regarding the location of the NOx sensors, I'm no expert but, what I did was located the square end (chip) of the NOx sensors and then followed the wiring all the way to the front end of the NOx sensor with the threading. Regarding your picture, if memory serves me right, I think number 2 is the downstream NOx sensor and the upstream sensor isn't shown in your picture. It is located farther in front and you'll need to remove a belly panel to see it. It is farther up on the top right side of your picture. Bottom line, located the big square end of the sensor (with the clip in the connector) and follow the wiring.
Bummer hearing that after replacing both NOx sensors and adapting them that the codes returned. Not comforting information.
Regarding the location of the sensors, I found more information online that I'd like to share. Your are absolutely correct about #2 in the photo I posted and it is indeed the rear or downstream NOx sensor. The forward or front NOx sensor, as you stated, is not pictured in my photo. I've attached a diagram of the exhaust system for your reference. N37/7 appears to be the upstream NOx sensor and N37/8 the downstream sensor.
Below is a post I discovered on YouTube that is related to this topic. I've posted one responder's comments to the video (text) on the NOx sensor replacement procedure.
The information below greatly helped me determine how I'll proceed. I plan to find an inexpensive front NOx sensor (computer and probe) and to replace myself to resolve the permanent P2201 DTC code. Hopefully I won't have the same issues as your brother in law.
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UPDATE: I just replaced both NOx sensors in 2012 ML350 Bluetec, and here's what you need to know:
Rear sensor is very straightforward. Jack the vehicle up and remove the transmission cover (it the second belly pan down on the vehicle). Using a standard Oxygen sensor wrench, loosen the downstream NOx sensor. It's about half way down the vehicle on the passenger side and after the catalytic converter. The sensor wiring is pinned up against the heat shielding with small metal brackets. Remove the wiring from the brackets. Then using 10mm and 8mm socket, remove the entire side rail plastic cover which extends alongside the passenger side of the vehicle near to the frame (about 8 inches wide and 2.5 feet long black plastic cover). There are about 10 or so bolts to be removed, many of them which connect heat shielding to the plastic cover. Once removed, you will see the downstream and upstream sensor computer boards bolted inside the compartment with 10mm hardware. Disconnect the computer board to wiring harness connector by using a screwdriver push out the grey tab, then insert carefully underneath the black bracket and separate.
Use the same procedure for the upper NOx sensor, aka THE PITA PART. The upstream NOx sensor is a PITA. The sensor is straightforward to unscrew from the exhaust. The computer board also not a problem. It's the wiring path that is a PITA. The wiring runs underneath the heat shielding. You'll need to locate several 8mm nuts that hold the heat shielding to the body of the vehicle and loosen those. They are a serious PITA especially the ones on the shielding up toward the large coffee can looking segment of exhaust coming from the headers that I believe is the first of two catalytic converters (either that or it's a sound dampener). The heat shielding is separated into three segments. Remove as many of the nuts as possible to loosen the shielding enough to pull the sensor out. Repeat procedure in reverse to position the sensor. Failing to protect the upstream wiring will expose it to significant heat that could compromise its longevity. Don't get lazy here. If too difficult get a spare piece of heat shield from parts yard, cut it to size and screw it up into the OEM heat shielding sandwiching the wiring in between (the lazy man's technique). PITA without a lift. Good luck, if you need any more advice or help, PM me.
Last edited by raisinbrann; Apr 25, 2019 at 10:11 PM.
The front NOx sensor was replaced successfully albeit with some difficulty.
Just a short summary of the effort. Please see photos.
1) Both transmission and passenger side underbelly panels must be removed to access front NOx sensor, probe and module.
2) The NOx computer module is easy to remove, but the probe was difficult. I needed to soak the probe nut with Liquid wrench for 24 hours and used an O2 wrench tool to break loose the nut.
3) Much of the heat shield will need to be loosened (nuts removed) so the NOx sensor or module probe cable can be slid behind heat shield.
Most of the effort was spent removing and reinstalling the underbelly panels - many fasteners. A car lift certainly would have been beneficial since working with the vehicle elevated on jack stands was difficult.
Plan on about 4 hours effort for the uninitiated, maybe 2-3 hours or less for the professionals.
I used an Autel diagnostic tool to re-calibrate the front sensor module. I have driven the vehicle about 750 miles and no CEL (Check Engine Light). The Autel tool showed the front NOx sensor module functioning normally in live mode. I did not replace the rear NOx module.
So far, so good. Have my fingers crossed.
I've attached a photo of the rear NOx sensor and module. Much easier to replace and only requires the passenger side underbelly pan to be removed.
Only negative is I'm missing one underbelly pan nut. :o
Hope you find this this information useful.
Last edited by raisinbrann; May 14, 2019 at 10:40 PM.
Reason: Missed a photo!
2013 ML350 Bluetec, 1966 Ford Mustang Convertible (sold)
Thanks for the great post with all the pictures. MY brother in law is still having the issue. We replaced both NOx sensors and cleared the codes, even readapted them (offline, not online coding on the MB server), but the check engine light comes back. It keeps saying there is no communication between them. I’m wondering maybe the sensors are bad (bad knock off company from China?!).
May I ask where you got the sensors from? I think I’ll return the old ones and try buying some from your supplier. Thanks.
Edit: another thread seems on the UK forums with same problems.
2013 ML350 Bluetec, 1966 Ford Mustang Convertible (sold)
So my BIL went to the MB dealership to have his new NOx sensors SCN online coded (relearned/readapted). On his drive back home the codes came back! The 2 NOx sensors are brand new. So it is either a wiring issue or the brand new NOx sensor is defective... I'll post another thread about this.
The front NOx sensor was replaced successfully albeit with some difficulty.
Just a short summary of the effort. Please see photos.
1) Both transmission and passenger side underbelly panels must be removed to access front NOx sensor, probe and module.
2) The NOx computer module is easy to remove, but the probe was difficult. I needed to soak the probe nut with Liquid wrench for 24 hours and used an O2 wrench tool to break loose the nut.
3) Much of the heat shield will need to be loosened (nuts removed) so the NOx sensor or module probe cable can be slid behind heat shield.
Most of the effort was spent removing and reinstalling the underbelly panels - many fasteners. A car lift certainly would have been beneficial since working with the vehicle elevated on jack stands was difficult.
Plan on about 4 hours effort for the uninitiated, maybe 2-3 hours or less for the professionals.
I used an Autel diagnostic tool to re-calibrate the front sensor module. I have driven the vehicle about 750 miles and no CEL (Check Engine Light). The Autel tool showed the front NOx sensor module functioning normally in live mode. I did not replace the rear NOx module.
So far, so good. Have my fingers crossed.
I've attached a photo of the rear NOx sensor and module. Much easier to replace and only requires the passenger side underbelly pan to be removed.
Only negative is I'm missing one underbelly pan nut. :o
NOX sensors are part of the emissions management and have an 8 year 80k mile warranty... (federal guideline) I had my NOX sensors and the heating element changed in my DEF tank at 78k miles on my 2012 ML350 Bluetec last year - just take it to the dealer...
NOX sensors are part of the emissions management and have an 8 year 80k mile warranty... (federal guideline) I had my NOX sensors and the heating element changed in my DEF tank at 78k miles on my 2012 ML350 Bluetec last year - just take it to the dealer...
Who's your dealer? My Benz dealer told me the NOX sensors were not covered under the emissions warranty, nor was the DEF heater which I had replaced fortunately just before my basic 4 year 48k mile warranty expired. Either I was lied to by Mercedes Benz or you have a very compassionate Mercedes Benz dealer.
Whether covered by warranty or not, hopefully this thread helped someone.....
BTW - love my diesel - but since Mercedes no longer sells diesel vehicles my next car will not be a Mercedes.
The NOx sensor is not specifically listed in the link above though it's certainly a component of the emissions system. Here's a quote from the link you provided above:
"The easiest way to find out if an emission component is covered under warranty is to contact your local dealer. The dealer can look up warranty information, including any additional warranties that may have been added to the vehicle since it was manufactured."
Again, I contacted my local Benz dealer about the failed NOx sensor and Check Engine light and they stated, I quote, "replacement of the NOx sensor is not covered under your vehicle's emissions warranty" and then provided me a repair estimate. Repair cost was well above of $1,000. Hence I replaced the sensor myself.
I just had both sensors changed by the dealer on my 2014 BLT. I drove around since last November with CEL, and should have kept refilling the DEF, as this last time when I refilled it did not reset the DEF count down. Fortunately, the Extended Warranty I had purchased covered the entire repair cost less $100 deductible, But you can bet, moving forward, i'll be doing the Delete for NOX, DEF and DPF and probably the EGR as well.
I just had both sensors changed by the dealer on my 2014 BLT. I drove around since last November with CEL, and should have kept refilling the DEF, as this last time when I refilled it did not reset the DEF count down. Fortunately, the Extended Warranty I had purchased covered the entire repair cost less $100 deductible, But you can bet, moving forward, i'll be doing the Delete for NOX, DEF and DPF and probably the EGR as well.
Who do you have your extended warranty with? I'm looking into getting one for my 2013 ML350 Bluetec
Hey,
I would suggest you reading this blog https://xenons4u.co.uk/blog/p229f62-...des-explained/ because this is related to your issue and also they explained all error codes in detail, I will feel glad if this helpful for you.
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