CEL/TracCont/4lo - help diagnosing

Truck threw codes P0171/P0174/C1201. Check engine and traction control are solid, 4lo is flashing.

No noticeable effect on driving, no sluggish start/acceleration, no limp mode. If the lights weren't on, I doubt I'd notice an issue. Can't feel/hear/see anything unusual.

From my research, I feel like I should start with the fuel pump and SAI bypass from Hewitt tech.

My questions are:
1. How can you diagnose a failing fuel pump, without displaying any symptoms? I have not been able to test the pressure yet. Would a failing pump still throw codes? I've always been able to tell it was going bad in the past...
2. Can the issue be the secondary air pumps, without ever reaching limp mode? Any way to diagnose this without just resorting to the bypass kit? Everything I've read is that this would result in limp mode... but I'm not there yet.

If anyone has any advice, I'd be appreciative. I'll have time to really dive into it next weekend, just trying to do as much preliminary research.

 

1. By the pressure I’m sure or maybe fuel trims. But there won’t be a code activated for anything that is still within allowed parameters.
2. Yes, it will not always go into limp mode with sais codes. I know this because mine did not… until it did later.

 

1. I hope to check the pressure soon. But it certainly feels like it would be within spec. No sputtering, no weird idle, no loss of power that I can tell.
2. I'll keep an eye on this. I don't have to drive to work until Friday, hopefully it doesn't hit me on my commute. Maybe I'll ask hewitt if they'll accept a return if it doesn't solve the problem. I'm not sure how to diagnose this besides just deciphering codes and process of elimination.

Thanks for the feedback!

 

I didn’t look up your codes. But if they are the sais codes it’s pretty likely the air injection. I think there is a sticky thread on this with your options.

 

Yep, they are those codes. I've read most of the threads as well. Just didn't know that I could have that issue and not be in limp mode, unless I missed a post/thread.

 

Following! I’m in the exact same boat!