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Just bought our 2012 GL 350 In December. After driving it ~1000 miles we got a CEL while vacationing in Florida. Autozone read the code P2202 and cleared it for me. Light stayed off for about 500 miles and came back on same code. This time I was at home and read it myself and cleared it again. It stayed off for a while and during that time I had the timing chain done and was hoping that maybe the timing being off from the stretched chain was causing it to run bad and throwing the codes - no luck.
I had a leak in the vacuum pump gasket from the timing chain job (indy shop) and while they were taking care of that the read the codes and looked at the sensors output and he said that it looked like it was reading so it wasn't a dead sensor.
Since then I've read through all that I can find and watched videos of the om642 SCR system and have tried a few things before just throwing money at parts.
I removed both NOx sensors from the exhaust - did not take the shields off to get to the modules. They both looked clean no soot/carbon looking build up. I didn't clean them any more than a quick wipe with a dry paper towel. and then reinstalled both.
After a 40 mile round trip while idling in driveway it came on. The engine sounded like the load had changed (AC compressor coming on???) and I saw the light come on.
I reset it and worked on getting my Torque App setup to monitor the NOx/Exhaust Temps/SCR temps... and started logging it all. Noticed that the Pre SCR NOx was lower than the Post SCR NOx most of the time but not always. Thought that was strange but both readings were moving up and down in relation to load (both would drop to 0 while coasting down exiting the highway for example) so I assumed that they are reading correctly.
Then before a 200 mile trip Saturday I (after watching a video on the NOx/SCR system) decided to pull the AdBlue injector to see if there was any crystal buildup. Yikes! Port was nearly completely plugged (See attached pics). Well I scrapped that out (got about a tablespoon of crystals between the injector and the port) and wiped it with distilled water. Made the trip and caught a Regen in the first half hour or so that lasted 10 min (according to the EGR and DPF Temps). So I thought everything was good. Got home ran some errands and while sitting in front of the store waiting on my wife to grab one last thing. I had the same sort of quick load change on the engine and the light came back on.
What concerns me is that the Pre SCR NOx readings are generally lower than the Post SCR readings. Is that an indicator of a Failing (or failed) sensor. I also read that if you replace a sensor you have to do a learn in process. Is that a Star Tool only thing that can do that or can any of the other scanner tools do that? I was looking at the iCarSoft Mercedes/Smart MB II. Or will the computer figure it out after time by itself? Also some threads say you have to replace both NOx sensors at the same time or it won't calibrate is that true?
Exhaust side nearly completely plugged
AdBlue injector
NOx readings from log - notice Post (orange) generally higher than Pre SCR readings.
Last edited by rosenhauer; 05-23-2017 at 01:46 PM.
Could you answer a few more questions before I order the sensor. Replace just the pre sensor or do both? Do you know if I can just install it/them or if an adaptation is required? if so can that be done with anything other than the star tool?
replace the one that is giving you trouble. they dont go in pairs.
dont know if you can do it without adaptation. i always have done it via the nox learning in star/ das tool. i am suspicious that you can just swap it, reset the errors and drive on with probably small reduction in performance. but i have no factual data.
i changed one on my gl320 and have no problems but it was difficult to diagnose until i did real time data on star tool and front nox would not activate
codes can be confusing on these, they are not like my wife's toyota van easy peasy
I replaced the front NOx sensor Thursday have driven several short trips (<30 miles) and longer one today. No Regens and no p2202 code. But it did throw a Pending P2BAD (NOx exceeded). The pre NOx does seem to be in a more reasonable range competed to before. Waiting to see if the pending code gets to be an actual code. Maybe I med too find someone local with a Star Tool to do an adaptation.
Local shop did the adaptation for the new Upstream NOx sensor and so far no codes
Rosenhauer i am having a P2201 code on my 2013 ML350 BT and i use torque too. However my value for Pre and Post NOx both are stuck at 2000PPM. It looks like yours actually moves according to your log. If i read your post correctly you cleaned the adblue injector and you still had to replace the NoX sensor then have it learned?
Ppms should move- usually somewhat in tandem. It takes up to 30’secs for the values to start changing once displayed in star/ das.
Can you help me regarding STAR/DAS. I want to buy a copy for my home use on this one vehicle. What do you recommend, somethign off ebay? I really just want to perform the tests and be able to relearn sensors, e.g. the NoX sensors.
The sensors have to be hot to work. I've noticed it can take 5 plus munutes sometimes to get hot enough if it's just idling. Until then it will just read max. The default PID I think that is the 2000. I was using a custom PID so mine go to 65384 until warmed up, even with the new sensor.
The sensors have to be hot to work. I've noticed it can take 5 plus munutes sometimes to get hot enough if it's just idling. Until then it will just read max. The default PID I think that is the 2000. I was using a custom PID so mine go to 65384 until warmed up, even with the new sensor.
Ok thanks. I am planning to buy STAR so i can relearn adaptations myself. I just dont know what i really need to buy.
05-23-2017, 01:38 PM
