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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.
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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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