Codes 171 and 174, warning chime?

Likely it's the chime to tell you to look at the dash because the CEL is on. Common way they try to get your attention. I would get the issue causing the light to be on repaired as driving a vehicle with a lean mix on both banks of the engine can cause the engine to run hot in the cylinders and damage the engine. A common cause is a vacuum leak or a bad intake gasket.

The chime just comes on a minute after I start my truck. I turn my truck off. Restart it. And it doesn't do the chime. The check engine light came on a week ago. The chime thing has been going on for 6 weeks. I've stopped driving it until I find the code problem. The truck is still driving Great . last time I took it out.

Okay, there are a few systems that can chime. When you turn the key on and the bulbs light up, does the air bag light work? You say it runs okay, any transmission issues? Check the washer fluid as well as coolant and brake fluid. If those all check out then I would pull all the codes, it's possible that a system is having an issue but not setting a code that turns on the light and is only triggering the chime. A full system scan may show it.

I haven't been able to find any vacuum leaks under the hood. Is there a vacuum to the fuel tank or transmission under the truck? All my fluids are right where they need to be. I changed the fuel filter 2 years ago. I changed the oil and filter about 6 months ago. And put new brake pads on the front and rear a year ago. I had a plug misfire on the #1 cylinder, so I just replaced all the plugs and ignition coils a year ago. And that was real fun. I only had 2 plugs break. Bought a plug puller for the 5.4. for $125.00. Totally worth it.

There is the EVAP purge line that runs back to the tank, if it was stuck open it might cause lean codes. If you have a scan tool that can read live data you can test the valve without a lot of fuss. You would run the engine and watch the fuel trims. Then you block the EVAP line and see if the fuel trims change to compensate for the lack of air from the leak. If you don't have a scan tool that can do that there are some reasonable ones out there or look at FORScan and the proper dongle. The windows version is as powerful as the OE tool and is much less money.