Question about 2004 Ford F150

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Codes #171 & 174

Have A 2004 Ford F150 Heritige 4.2 2wheel drive,auto, Check engine light is on ,showing code 171 &174 con you fix this problem.

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  • Anonymous Jan 08, 2009

    had code 174 & 171: replaced vacuum hose from valve cover to pcv, cleaned injectors and installed new fuel filter. service engine light comes back on and code is now 174 only. when i re-set the light before a long trip (300 miles+) the light stays off (this happened twice) but as soon as i start driving around town it comes back on within 15-20 miles. mileage has dropped from nearly 20mpg to 17.5 on trips and it has gotten worse around town. any suggestions as to what to do next?

  • Anonymous Feb 05, 2009

    I have a 2003 Ford F150 with a 4.2 liter that has troble code 171 and 174. I was told to replace the Mass Air Flow sensor which I did but it did not correct the problem . I was also told it could be a bad O2 sensor but there are 4 of them and I have no I idea which one might be bad. I was also told to check the vacuum hose to PCV but have no idea where it is located.

    Can someone help me?

  • ramendoza19 Mar 29, 2009

    I have a 2003 4.2l v6 f150 and I originally had codes p171&p174 so I took my truck to city garage and spent $110.00 on a new maf did not fix the problem so I replaced the ruel filter, cleaned the injectors, replaced all 4 o2 sensors. So now I am going to replace the EGR valve hoping thats what the problem is I will let you know.

  • Anonymous Mar 15, 2014

    Ford says cats are going bad?



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first check out for o2 sensor if its faulty this can show up.but if its proper.Evaporative emission control system leak very small 171 System too lean (bank 1) 174 System too lean (bank 2) 

Posted on Jan 05, 2009


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