Lethal Emissions exhaust
Thread Starter
Junior Member
Joined: Jun 2010
Posts: 63
Likes: 25
From: CT
'21 GLC 300, '13 C300 Sport
Lethal Emissions exhaust
Emissions history:
5/18/21 62K miles - Emissions Modifications completed by dealer
8/23/24 87K miles - upstream temp sensor on exhaust replaced (under warranty)
10/20/25 97K Miles - CEL light came on, then 2 days later.... after parking in my garage, I smelled a suffocating ammonia-like odor coming from tailpipes.
Brought to local dealership who performed the emissions mods. Their diagnosis, after 3 days, was a faulty adblue temp sensor inside the DEF tank. Part ordered, took another 5 days before got call that it was ready to go. (Had new loaner vehicle during this time)
They said it was covered under the extended warranty
Drove home OK, Then when I went to work, within 2 miles on the highway engine light came back on, and potent adblue smell (and faint steam-like exhaust) coming again from exhaust.
I'm guessing they didn't get this up to full running temperature to test the emissions system properly? At any rate, it's back at the dealership now and will see what they find this time around. Either the injector is stuck open and letting too much DEF fluid to be released, or another faulty sensor causing it to. We'll see...
5/18/21 62K miles - Emissions Modifications completed by dealer
8/23/24 87K miles - upstream temp sensor on exhaust replaced (under warranty)
10/20/25 97K Miles - CEL light came on, then 2 days later.... after parking in my garage, I smelled a suffocating ammonia-like odor coming from tailpipes.
Brought to local dealership who performed the emissions mods. Their diagnosis, after 3 days, was a faulty adblue temp sensor inside the DEF tank. Part ordered, took another 5 days before got call that it was ready to go. (Had new loaner vehicle during this time)
They said it was covered under the extended warranty
Drove home OK, Then when I went to work, within 2 miles on the highway engine light came back on, and potent adblue smell (and faint steam-like exhaust) coming again from exhaust.
I'm guessing they didn't get this up to full running temperature to test the emissions system properly? At any rate, it's back at the dealership now and will see what they find this time around. Either the injector is stuck open and letting too much DEF fluid to be released, or another faulty sensor causing it to. We'll see...
Super Member
Joined: Mar 2013
Posts: 915
Likes: 185
Yikes:
Emissions history:
5/18/21 62K miles - Emissions Modifications completed by dealer
8/23/24 87K miles - upstream temp sensor on exhaust replaced (under warranty)
10/20/25 97K Miles - CEL light came on, then 2 days later.... after parking in my garage, I smelled a suffocating ammonia-like odor coming from tailpipes.
Brought to local dealership who performed the emissions mods. Their diagnosis, after 3 days, was a faulty adblue temp sensor inside the DEF tank. Part ordered, took another 5 days before got call that it was ready to go. (Had new loaner vehicle during this time)
They said it was covered under the extended warranty
Drove home OK, Then when I went to work, within 2 miles on the highway engine light came back on, and potent adblue smell (and faint steam-like exhaust) coming again from exhaust.
I'm guessing they didn't get this up to full running temperature to test the emissions system properly? At any rate, it's back at the dealership now and will see what they find this time around. Either the injector is stuck open and letting too much DEF fluid to be released, or another faulty sensor causing it to. We'll see...
5/18/21 62K miles - Emissions Modifications completed by dealer
8/23/24 87K miles - upstream temp sensor on exhaust replaced (under warranty)
10/20/25 97K Miles - CEL light came on, then 2 days later.... after parking in my garage, I smelled a suffocating ammonia-like odor coming from tailpipes.
Brought to local dealership who performed the emissions mods. Their diagnosis, after 3 days, was a faulty adblue temp sensor inside the DEF tank. Part ordered, took another 5 days before got call that it was ready to go. (Had new loaner vehicle during this time)
They said it was covered under the extended warranty
Drove home OK, Then when I went to work, within 2 miles on the highway engine light came back on, and potent adblue smell (and faint steam-like exhaust) coming again from exhaust.
I'm guessing they didn't get this up to full running temperature to test the emissions system properly? At any rate, it's back at the dealership now and will see what they find this time around. Either the injector is stuck open and letting too much DEF fluid to be released, or another faulty sensor causing it to. We'll see...
Lethal?
Out Of Control!!
Joined: Jun 2004
Posts: 13,799
Likes: 3,228
2014 E63S; AMS 100 octane ECU dyno tune; EDOK TCU tune; BB intakes; sprintbooster
I re read your post - you didn't mean someone died - which lethal suggests.
you probably wanted to use the word noxious or something like that.
got it.
Sorry for your troubles
you probably wanted to use the word noxious or something like that.
got it.
Sorry for your troubles
Last edited by PeterUbers; Oct 30, 2025 at 05:34 PM.
MBWorld Fanatic!
Joined: Sep 2015
Posts: 2,583
Likes: 342
2013 glk 350
Your lucky !! You’re under warranty! Just think if it wasn’t covered . Yea the diesel motors are great, the pollution controls ruined them . I would not buy one because of what you’re going through . It’s very common . I’m sure resale value proves that .
Out Of Control!!
Joined: Jun 2004
Posts: 13,799
Likes: 3,228
2014 E63S; AMS 100 octane ECU dyno tune; EDOK TCU tune; BB intakes; sprintbooster
Trending Topics
MBWorld Fanatic!
Joined: Sep 2013
Posts: 2,346
Likes: 691
2021 GLB250 FWD, 2023 GLA250 FWD, 2013 C250, 2015 GLK350, 2005 ML350SE, 2003 E320
FWIW
Anhydrous ammonia (NH3) has a 30 minute escape time at 300 PPM (0.03%) without lasting health effects. Dangerous because it reacts with moisture in the lungs causing tissue damage.
Ammonium hydroxide vapor NH4OH which is what we normally think of as the ammonia smell can but seldom reaches dangerous concentration in air.
8 hour workplace exposure limits (US)
NH3 - 25 PPM odor is unreliable for detection of NH3
NH4OH - 50 PPM which is also the odor threshold
Anhydrous ammonia (NH3) has a 30 minute escape time at 300 PPM (0.03%) without lasting health effects. Dangerous because it reacts with moisture in the lungs causing tissue damage.
Ammonium hydroxide vapor NH4OH which is what we normally think of as the ammonia smell can but seldom reaches dangerous concentration in air.
8 hour workplace exposure limits (US)
NH3 - 25 PPM odor is unreliable for detection of NH3
NH4OH - 50 PPM which is also the odor threshold
MB World Stories
The Best of Mercedes & AMG
Manual Mercedes? 6 Times Sindelfingen Let Drivers Have All The Fun
Verdad Gallardo
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Verdad Gallardo
8 Classic Boxy Mercedes Designs That Have Aged Like Fine Wine
Verdad Gallardo
Flawlessly Restored Mercedes 190E Evo II Heads to Auction
Verdad Gallardo
Electric Mercedes C-Class Unveiled: 11 Things You Need to Know
Verdad Gallardo
Mercedes EQS Gets A Major Update: Everything You Need to Know
Verdad Gallardo
5 Underrated Mercedes-Benz Models That Don't Get the Love They Deserve
Verdad Gallardo
Mercedes 300D Has Pushed Well Past 1 Million Miles and It Ain't Stopping
Verdad Gallardo
10 Most Reliable Mercedes-Benz Models You Can Buy Used
Verdad Gallardo
Super Member
Joined: Mar 2013
Posts: 915
Likes: 185
Yikes:
Thread Starter
Junior Member
Joined: Jun 2010
Posts: 63
Likes: 25
From: CT
'21 GLC 300, '13 C300 Sport
Super Member
Joined: Mar 2013
Posts: 915
Likes: 185
Yikes:
The ammonia smell, being repulsive and an irritant to the lungs, is a good thing as it alerts you to a problem/situation unlike the "silent" killer, carbon monoxide. Ammonia-based "smelling salts" are used to bring people back to consciousness and not to kill them although I'm sure, in a sufficient concentration, it could kill.
Last edited by MBKLUE; Oct 31, 2025 at 09:12 AM.
MBWorld Fanatic!
Joined: Jun 2021
Posts: 3,107
Likes: 1,345
From: Fleriduh
W212 E63S Wagon - GSL580 - E63 - E350 - C300
The ammonia smell, being repulsive and an irritant to the lungs, is a good thing as it alerts you to a problem/situation unlike the "silent" killer, carbon monoxide. Ammonia-based "smelling salts" are used to bring people back to consciousness and not to kill them although I'm sure, in a sufficient concentration, it could kill.
You should change your username to Fritz Haber!!!! :-) :-) :-)
Thread Starter
Junior Member
Joined: Jun 2010
Posts: 63
Likes: 25
From: CT
'21 GLC 300, '13 C300 Sport
Haven't heard a peep yet from dealership; not to be dramatic or anything, but I hope all the diesel mechanics are OK. Rumor has it the entire service department has been put under quarantine, while they await an emergency response team to arrive from Stuttgart to assess and remediate the situation. I fear my car will forever be labeled as 'vehicle zero' and have zero remaining value. Maybe they will never reopen, and I'll be able to keep the brand new GLA 250 'courtesy vehicle' indefinitely; not a bad ride!
MBWorld Fanatic!
Joined: Jun 2021
Posts: 3,107
Likes: 1,345
From: Fleriduh
W212 E63S Wagon - GSL580 - E63 - E350 - C300
Meh, it was the Chicken Salad....I will go out and fire up my diesel in your honor.....(I do need to find a slow oil leak that I am certain I created)...maybe I should dump the black water tank onto my driveway in your honor....
Thread Starter
Junior Member
Joined: Jun 2010
Posts: 63
Likes: 25
From: CT
'21 GLC 300, '13 C300 Sport
Update: dealership replaced both upstream and downstream NOx sensors. I still smell a little bit of the exhaust odor, but not anything like it was, didn't knock me over
Junior Member
Joined: Sep 2025
Posts: 56
Likes: 14
From: CT
2010 GLK350 4matic
I see you’re from CT. Hopefully the dealer that did the work isn’t the one in North Haven. They are thieves. My car was in for warranty subframe replacement and they attempted to charge me labor to R&R the springs and exhaust. Those things have to come out as part of the warranty work.
Thread Starter
Junior Member
Joined: Jun 2010
Posts: 63
Likes: 25
From: CT
'21 GLC 300, '13 C300 Sport
Nope not going there. Went for trip yesterday (15 miles each way), and on way back engine light came back on, but only a mild smell of ammonia; have to bring it back again, the drama continues 
MBWorld Fanatic!
Joined: Jun 2021
Posts: 3,107
Likes: 1,345
From: Fleriduh
W212 E63S Wagon - GSL580 - E63 - E350 - C300
Wait, the genius squad at the Stealership did not get this clearly earth destroying issue with your atmosphere killing - selfish mode of transportation? I will report them immediately to crconsulting for retraining to get up to that expert status.........never, I mean never trust anyone but a "Mercedes Dealership" mechanic.
Thread Starter
Junior Member
Joined: Jun 2010
Posts: 63
Likes: 25
From: CT
'21 GLC 300, '13 C300 Sport
Finally have car back after 10 days at dealership..... this go around the SCR was replaced, along with upstream NOx sensor (which was already replaced on previous stayover). They kept it for awhile, drove it some 80 miles in all to be sure CEL didn't pop up again.
