Check engine light on and codes 171, 174 and 401

Tiny
PIGHUNTER819
  • MEMBER
  • 1996 ALL OTHER MAKES ALL OTHER MODELS
I have a 96 F-150. 4.9L inline six engine. My check engine light came on. Trouble codes read 171(System too lean bank 1) 174 (System too lean bank 2) and 401 (EGR flow insufficient). Where is a good place to start? Truck seems to run sluggish and sometimes after stopping from high speed on the highway it will stall. Any help will be great.
Saturday, February 24th, 2007 AT 4:40 PM

1 Reply

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good evening,

The 171,174 are lean codes.

You need to test for vacuum leaks as that is common. Make sure the PCV valve is also working.

https://www.2carpros.com/articles/repair-lean-mixture-codes-p0171-or-p0174-on-some-manufacturers

Also, check the fuel pressure. Low fuel pressure will also cause this code.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

The 401 is for the DPFE sensor. Very common failure. When you replace it, make sure the lines are replaced as well.

Roy
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Wednesday, March 25th, 2020 AT 4:00 PM

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