Need help with a U0074 code

zporta · Mar 20, 2015

I have a 2014 with a Mini Maxx and gear head tuning, EGR/DPF delete and a s&b intake. Everything has been installed for 10k and 8 months without a single change.

After my Dad borrowed my truck to pick up some lumber i noticed a check engine light right when i jumped in. Not sure what could have happened or changed for the 30 min he had my truck i checked the DTC on my tuner and got U0074-Control Module Communication Bus B Off.

I tried clearing it a few times but it kept coming back upon the next start up or two. I also tired clearing it and then disconnecting the tuner to eliminate the idea of a bad HDMI connection, came right back. I contacted Gearhead and they gave me a few things to try and assured me its not tune related. I also returned the truck to stock and then reloaded the tune. It went away for a quick stroll around the block, and my 15 min drive home. I thought it was fixed until this morning i started the truck and it was back.

Out of ideas here, didn't come up with much info on a google search. I tried calling H&S but only got the machine.

Anyone had this or have any clue?

samsquatch47 · Mar 20, 2015

Check all of your old exhaust sensor plug ends that should be tied up under the truck. They should be all blown out with air then filled with dielectric grease. Also make sure the NOx module is unplugged. And then fill the connector with grease too. It's a silver box bolted to the passenger side inner frame rail about inline with the rear passenger door. Then go to your fuse box under the hood and check #36 I believe. Replace it if blown. Clear the codes and should be good now. Either that NOx module or one of the old sensor plugs shorted and cause the truck to throw the code. Hope that helps!

samsquatch47 · Mar 20, 2015

If the connector plugs aren't filled with grease corrosion can build up in them and can cause a short. Sometimes the NOx box just shorts too. If none of this works probably the glow plug control module, it's on the same circuit as all the exhaust emission crap. But usually they throw the U0106 code as well if that module goes, also the glow plug light may flash on initial key on before a cold start.

zporta · Mar 20, 2015

^ I will try that, but shouldn't all the sensors be disabled through the tune?

samsquatch47 · Mar 20, 2015

Sensors are yes, the truck should no longer look for them with a tune. but power goes through the wires and connectors still. So if some moisture gets in the plug ends it glitches. Plus for whatever reason that NOx box shorts out too, so unplugging it takes it out of the equation.

20156point7 · Mar 20, 2015

I had this same problem until I unplugged the nox sensors and no more codes after that

zporta · Mar 23, 2015

Are there 2 nox boxes? There was one on the outer side of the frame trail and one on then inside further back

I disconnected both of them and sprayed electric cleaner in all the connections and filled them full of di-electric then electrical taped them shut. So far so good

samsquatch47 · Mar 25, 2015

I know the inner frame rail is the one I unplugged I didn't see the outter?... I followed the inner wires and they went to the sensors in the exhaust. Where did the wires from the outter frame run to?

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zporta · Mar 25, 2015

samsquatch47 said:
I know the inner frame rail is the one I unplugged I didn't see the outter?... I followed the inner wires and they went to the sensors in the exhaust. Where did the wires from the outter frame run to?

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The front exhaust sensors, everything has been unplugged, cleaned, greased and taped up for 3 days and no codes

samsquatch47 · Mar 27, 2015

zporta said:
The front exhaust sensors, everything has been unplugged, cleaned, greased and taped up for 3 days and no codes

Awesome news man glad I could help!

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Trevor008 · May 27, 2015

Were any other symptoms associated with this other than the code and light? Can a glitch from these sensors cause remote start to stop working and issues with the nag screen functions?

dsmracing1 · Jul 25, 2016

Great info here fellas! I've been driving chitty muddy roads for a few days and had this pop up. I'll wash the underneath of my truck and deal with these connectors and nox box too...

MBR6.7 · Feb 2, 2021

I just ran into this same issue but I am getting both U0074 and U0106. Any suggestions on fixing the U0106? I'm going to do the electric cleaner and grease since I just got the truck tuned/******d recently and I didn't tape off the open connections. PLus it literally snowed the last two days in my area so I'm positive this is the result of this but I am unaware of why the glow plug fault. Thanks!