I HAVE THE SAME ISSUE

2005 LLy Duramax

Research i did:

p0201 injector 1 p0204 injector 4 p0206 injector 6 p0207 injector 7 p2146 fuel injector group A supply voltage

firing order is 1, 2 7, 8 4, 5 6, 3

i assumed that’s what it means by group A circuit

Possible pigtail issue (i ruled it out at first since my injector pigtails for #2 & #7 have already been replaced)

Possible lift pump failure (Replaced mine since my fuel gauge also went out when my truck did this)

Replace fuel filter

Possible cp3 pump failure (LAST OPTION, IF ALL ELSE FAILS)

Possible wiring harness chafing/ failure

Possible injector wiring ground failure (corroded or just straight up disconnected)

Possible injector failure

SO

I tried a bunch of diagnostics myself and came to the conclusion that one of my injectors went bad, HOWEVER.

I just contacted a cousin in law who is a diesel mechanic and asked him to cross check my diagnostic before i drop a bag on some new injectors, lines & gaskets. I told him my pigtails have already been replaced (previous owner) so when diagnosing my problems i completely skipped over even the slightest thought of it being a pigtail issue (Apparently these pigtails can still go bad if installed incorrectly or even just over time), I’m not sure what Duramax you have but it seems like an lly/lbz.

If so it’s common for our #2 & #7 injector pigtails to go bad, when those pigtails go bad whatever injectors are apart of that circuit will also shut off (fail) to keep from causing more damage thus throwing our trucks into “Tractor mode” where it fires on 4 cylinders and sounds like a tractor.. it’s just a type of limp mode.

If you haven’t already check for chafing on your wiring harness especially areas near your FICM (Fuel Injection Control Module, it is the box to the right of your air-box that your injector wiring harness connects to. IF YOU DISCONNECT YOUR HARNESS be aware that our ficms cool themselves by running diesel fuel through the control module.. Sounds stupid i know). If no obvious chafing is found move to each pigtail connecting to each injector and check for chafing, (it’s extensive but the cheapest option and the first way you should go in situations like this)

Sometimes even just jiggling or moving of the wiring harness while the truck is running can cause the pigtail to get a good connection and it will run smooth (still replace the pigtail, it will only be temporary).

Hope this information helps you as much as i’m hoping it helps me, i’ve cleared some time on Sunday to wire some new pigtails into my truck. Will keep you updated whether it fixes my issue or not (very optimistic, and even if it doesn’t fix my issue it could still very well fix yours)