Long story short: 97 F150 5.4. CHk ENG light on. Code 171. Chk everything on this forum. Disconnect neg bat. Light off, drive two days, get emissions test. Pass w/no codes. Stop and get gas. Light on. Is it possible or impossible that a bad (aftermarket keyed) Gas Cap can cause these conditions? Is it OK to drive without engine damage with CHK ENG light on? Thanks.

 

You should get it checked for free at an autozone if there is one near you, the gas cap could cause it but there is only one way to see if that is the problem. Did you just install the cap?

 

It is not new. OLD. I thought that emissions would have checked it but I think he only looked at it. I did take it off for him. When it came on after stopping for gas and taking cap off (second time in minutes) it got me thinking. I will replace it if someone here says it's possible. I guess JRSCOT, you are saying it will cause code 171/Light on condition? (among many other causes)

 

Bad cap or cap off will cause the check engine light to come on.

Replace with original or new and see if light goes out if you can't go pull the codes.

Has to do with monitoring the evap controls.

My smog guy says some Mercedes fail the cap test. Guys are PO'd that their expensive buggy spits out such a cheap part so soon.....

 

Thank you. You are giving this OVALHEAD great hope. I will replace tomorrow.

 

A gas cap can NOT cause a P0171 code. A P0171 code is most likely due to a vacuum leak.

A faulty gas cap on a 97 will cause either a P0455 or P0442 code depending on how much it's leaking. No other codes will be set by a leaking gas cap.

Steve

 

or an P0440...Large leak

 

Not on a 97. P0455 is a large leak, p0442 is a small leak.

P0440 is a non-existent code for 97-02, at a minimum.

P0456 was added at some point by 2002 for a VERY small leak.

Steve

 

Well i know i did a late 99' silverado that had a P0440....so i just crossed it over.

 

That was a Chevy. Ford hasn't used that code.

Steve

 

It is not always the cap that's bad. I dropped the right rear wheel in a hole and slammed the receiver and right corner of the bumper real hard. It flexed the bed enough to crack the plastic fitting that connects the gas cap to the hose going to the tank my lucky day.

 

What the hell are you guys talking about? Why don't you PM each other?

 

If you can't keep up maybe you should try another thread...

 

If you weren't acting like this is a chat room, you would have noticed this is MY thread. Stay on topic and offer some answers please.

 

My check engine light went on on my pickup so I went to autozone and got it plugged in and I got a code. The guy there knew fords real well, so he knew what that code was for and it was for an air leak somewhere in the fuel system. He sayed that it was probably the gas cap was leaking air, so I bought a new one, disconnected, and reconnected the battery cables and the light turned off. $10.00 gas cap