NOx sensors threw CEL, but CEL now off - bad diesel?
Thread Starter
Newbie
Joined: Aug 2016
Posts: 7
Likes: 0
Mercedez Benz ML 350 BlueTec 2012
NOx sensors threw CEL, but CEL now off - bad diesel?
Was on a road trip and after a gas stop CEL came on. At dealership next day, it showed fault codes 300 and 121 for upstream and downstream NOx sensors needing replacement. Cleared codes, immediately came back on. Needed my car, so agreed to come back in as soon as the starts remaining countdown came on. Got a new tank of diesel in town (18 gal), and CEL went off the next day and has been off since (1 week).
Has anyone ever seen this with their Bluetec? We're thinking it could have been a bad tank of diesel and that rather than failing, the NOx sensors actually sensed it..... and then sensed when the clean diesel was put in, turning off the CEL. Am I reaching and we should just get the NOx sensors cleaned or replaced? Thoughts? Thanks!
Has anyone ever seen this with their Bluetec? We're thinking it could have been a bad tank of diesel and that rather than failing, the NOx sensors actually sensed it..... and then sensed when the clean diesel was put in, turning off the CEL. Am I reaching and we should just get the NOx sensors cleaned or replaced? Thoughts? Thanks!
Member
Joined: Jan 2014
Posts: 236
Likes: 30
From: Florida
2013 ML350 Bluetec, 2016 C3, 2020 Lincoln Aviator
Last year I had the fault code for upstream and downstream NOx sensors, P0229 code. The P0300 and P0121 do not apply to NOx sensors.
Something is off in your story....
Something is off in your story....
Thread Starter
Newbie
Joined: Aug 2016
Posts: 7
Likes: 0
Mercedez Benz ML 350 BlueTec 2012
Hmmm. Well, CEL came on - went to the dealer, the paperwork says:
"scan for fault codes - found stored code only for NOX sensors (2) - clear codes and reset systems. If light comes back on both nox sensors will have to be replaced - estimate $1800."
I asked what the codes were and they said 300/121. I said not a P code? They said no, just 300 and 121 (not P0300 and P0121 as you said above). CEL immediately came back on, but went off the day after we got new gas.....
Service Mgr said he was not surprised that the CEL went out, but that the NOx sensors would both still need to be replaced at some point..... Just curious to me that BOTH would "fail" simultaneously, upstream and downstream if it wasn't something like bad fuel.... but what do I know? :-)
"scan for fault codes - found stored code only for NOX sensors (2) - clear codes and reset systems. If light comes back on both nox sensors will have to be replaced - estimate $1800."
I asked what the codes were and they said 300/121. I said not a P code? They said no, just 300 and 121 (not P0300 and P0121 as you said above). CEL immediately came back on, but went off the day after we got new gas.....
Service Mgr said he was not surprised that the CEL went out, but that the NOx sensors would both still need to be replaced at some point..... Just curious to me that BOTH would "fail" simultaneously, upstream and downstream if it wasn't something like bad fuel.... but what do I know? :-)
Last edited by PaintedQuail; Aug 11, 2018 at 05:22 PM.
Senior Member
Joined: Sep 2012
Posts: 323
Likes: 31
From: Ottawa ON Canada
2015 ML350 Bluetec
I, too, on a trip to FL last winter, discovered the pain of failed NOX sensors. Fortunately, the Ft Myers dealer replaced them under warranty... mine is a 2015. I was armed with all sorts of data that the NOX sensors are part of the Emission Warranty(8yrsI believe), but didn't have to argue! Not sure as mine was still under its orig warranty?? My sense was the same as yours, bad fuel purchased somewhere on the trip south..... glad yours 'recovered'! $1800 for 2 sensors???? It didn't take the dealer much time to replace mine and.... wash the car... LOL!
Super Member
Joined: Dec 2013
Posts: 628
Likes: 176
From: SW Ontario Canada
2020 GLS580, 2023 Corvette Z06
I, too, on a trip to FL last winter, discovered the pain of failed NOX sensors. Fortunately, the Ft Myers dealer replaced them under warranty... mine is a 2015. I was armed with all sorts of data that the NOX sensors are part of the Emission Warranty(8yrsI believe), but didn't have to argue! Not sure as mine was still under its orig warranty?? My sense was the same as yours, bad fuel purchased somewhere on the trip south..... glad yours 'recovered'! $1800 for 2 sensors???? It didn't take the dealer much time to replace mine and.... wash the car... LOL!
Senior Member
Joined: Sep 2012
Posts: 323
Likes: 31
From: Ottawa ON Canada
2015 ML350 Bluetec
Well, I don't have all the data that I hiked into Fort Myers with, but, I was still under my initial warranty. I also have and Extended Limited Warranty. All that said I went into MB Canada website and browsed through their warranty statement. As you can see some emmissions are covered for 2yr/40K, while others are for 8yr/130k. Now I was definitely over 2yrs, and had about 65k kms, so I'm not sure how they work it??? I have included a PDF of my bill. Note: the mileage is in miles(US). Hope that helps
New Car Warranty
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
