[Greck]

Hi All,
The "SCR Functional check" says that I have to replace the SCR catalytic converter, I even bought one for replacement, and visited the mechanic, but guy who is doing welding works told me that I have to check everything one more time because he can't believe that 2011 car needs the replacement, by his explanation "bad" cat is cat full of soot, but my car runs great and it means that cat is clean. Usually car looses it's power when cat is full of soot. One of his idea that there is something else can tell to the Engine ECU that can leads to cat, but it is definitely not a cat. What do you think about that?

[BB_cuda]

There is a cat within the DPF called a DOC (diesel oxidation catalyst). There is a different cat in the SCR. It is an ammonia reactor to scrub the NOx. Briefly, urea is heated up to then convert to ammonia. The ammonia reacts with SCR bed and exhaust gases to make GN2 and water, reducing the NOx output.

You need to be careful how you are interpreting the cat info. If normal DPF is in place, the SCR shouldn't be getting sooted up. The DOC will see soot. The welder is using a viewpoint more on the gasoline engine front.

[Greck]

Originally Posted by BB_cuda

There is a cat within the DPF called a DOC (diesel oxidation catalyst). There is a different cat in the SCR. It is an ammonia reactor to scrub the NOx. Briefly, urea is heated up to then convert to ammonia. The ammonia reacts with SCR bed and exhaust gases to make GN2 and water, reducing the NOx output.

You need to be careful how you are interpreting the cat info. If normal DPF is in place, the SCR shouldn't be getting sooted up. The DOC will see soot. The welder is using a viewpoint more on the gasoline engine front.

I told him that there is another cat called "DPF" so he knows about that... For me it is not clear... if DPF is not good enough why the system test points to the SCR Cat? Is there any system test for DPF?

[BB_cuda]

Firstly, talking to wrong guy about running system testing. Clarification also in that DPF "container" has DOC in front and diesel particulate filter in the aft section.

Floydrogers is pretty knowledgeable on this front. Hopefully, he'll be along soon to offer input.

[Hoooper]

Whats your mileage? SCR is covered under warranty for 7 years/70k miles.

[Greck]

113k

[BB_cuda]

if you don't ask for a freebie, the answer will always be no. I'd hear out Floyd first though.

[Greck]

I don't know who is Floyd, but I hope he can clarify this situation. I will replace the cat at the end of next week probably and will collect the ideas and opinions till that point. Thank you.

[Hoooper]

Did you test out the nox sensors? Cant remember if you tried that. The DDE uses nox sensor feedback to determine if the SCR cat is good so if a nox sensor is bad you can get a false positive on the SCR cat being bad. A clogged DEF metering valve causing low flow or poor spray pattern could also cause a false positive on the SCR cat.

[Greck]

Originally Posted by Hoooper

Did you test out the nox sensors?

I replaced both of them... but how I can test them?

[Hoooper]

Originally Posted by Greck

I replaced both of them... but how I can test them?

Well, replacing them with good ones works. You can also try switching their positions and see if the code changes, but since you got new ones id say its not likely to be them. Only other thing to check would be the metering valve flow and pattern. If thats good...

[ingenieur]

Your test showed only a 41% NOx conversion rate - since the NOx sensors are new OEM - right?, metering valve is dosing the correct amount, DEF is new then your SCR catalyst is the cause as the test indicated. Usually it is an aging sensor(s) or metering valve issue....
With a new SCR catalyst > 90%

[Greck]

Originally Posted by Hoooper

. Only other thing to check would be the metering valve flow and pattern. If thats good...

It was the first thing that I did. Metering Valve sprayed the same amount of urea that ISTA expected, so it PASS the ISTA tests.

[Greck]

I bought front sensor new and rear used from car with 60k miles on odometer. I guess I can replace it again with new one and replace the metering valve just in case if they are not good enoght

[Greck]

Typically I have to erase the "SCR system inefficiency" error every day on\after my way back from home, but this weekend I decided that probably I have to wait few more days and see what happens, probably another codes will appears, but after 3 days and about 200 miles I still have only one code... 4D16 SCR System, efficiency, does anybody have any other ideas instead of replacing the SCR Cat? Should I check something else before? Thanks.

[335duff]

I've had 4D16 a few times and i believe they replaced the scr metering valve, I will check when I get home

[HeyDouglas]

Had the same code last year. I can't remember if there were other codes. Dealer replaced scr under warranty. Metering unit wasn't covered for some reason. I replaced the metering unit myself.

[Greck]

Originally Posted by 335duff

I've had 4D16 a few times and i believe they replaced the scr metering valve, I will check when I get home

Please check it

[Greck]

Originally Posted by HeyDouglas

Had the same code last year. I can't remember if there were other codes. Dealer replaced scr under warranty. Metering unit wasn't covered for some reason. I replaced the metering unit myself.

They replaced SCR Cat?

[Hoooper]

Originally Posted by Greck

I bought front sensor new and rear used from car with 60k miles on odometer. I guess I can replace it again with new one and replace the metering valve just in case if they are not good enoght

Try switching their locations, back to front

[Greck]

Originally Posted by Hoooper

Try switching their locations, back to front

Are they identical? It is safe to do it? Is length of the wires fits both locations?

[eric-satx]

I had that code too. Under CPO they replaced NOx sensors but finally had to replace the SCR cat to get it to stay away. Took 5 months to get in from Germany.