Alright, so my Dad has a 97' Bonneville that he'* been having trouble with. Here'* some history:

Car: 97' Bonneville with 88k miles
About 10k ago it had the lower intake manifold problem which was replaced. ($$$ wasn't pretty)

Then about 5k miles ago it threw a CEL, it was P0171 according to the local chevy dealership.
They first replaced/cleaned all the battery cables.
Code went away....
Code came back....
Then they replaced the fuel pump, they said the fuel pressure was low (25-30psi), and that a fuel pump should take care of it (def got overcharged on that also IMO)
Code went away...
Code came back...
Then they replaced the oxygen sensor.
Code went away....
Now the damn code is back...

Searched this site (very informative BTW) and it turns out that all of the above are common fixes for this mystery code. But my question is then why is it back?
I also read on this site that it could be the Evap Purge Valve which I know nothing about. Perhaps someone could shed some light on this for me?
And I read as well about plug wires touching the o2 sensor could cause this....Now I'm very familiar with my Subaru, but not with GM what-so-ever. I'm assuming the o2 sensor is on the exhaust manifold (right?) but could someone help me with the orientation.

Also, if anybody knows any other causes of this code p0171 that that would help us out greatly. Thanks.

O2 sensor is on the rear exhaust manifold. Did all the battery cables get replaced?

Here'* a picture of the O2 sensor, right about below the #4 spark plug.


As TT mentioned, the battery cables have been known to be an issue with that code. Double check their cleaning and/or replacement. The positive cable is really 2 pieces under the boot. If that wasn't replaced, pull that boot off and clean it up. Clean up both ends of the cables. Also check the ground under the ICM (ignition control module) which is what the coils are attached to.

I'm a premier member in the P0171 club and plan on a fuel pump soon. There'* one possible piece to the puzzle that I'm waiting on and that'* the evap purge valve and a switch where other years only have a purge valve. Not sure if there'* any merit it in..but worth a mention. Typically the issue is a poor battery/ground connection.

Thanks guys, this is just the type of info I'm looking for.

Archon, thanks for that picture, I'm gonna check it out tomorrow morning first thing. It'd be nice if I could repair it by moving some wires around. How do you recommend I keep them seperated if I find this to be the case?

BillBoost, through my research on this site I gathered you were familiar with this annoying cel. Thanks for the info, though I'm still confused, does the evap purge valve have to be replaced with one that has a switch? Or does the 97 have a switch and this is causing some malfunction? Let me know.

Thanks again

EDIT: Not sure how many battery cables got replaced or just got cleaned or even if they all got cleaned so I'll have to check on that tomorrow too. Thanks.

I routed my #6 plug wire along the back of the rear valve cover and then down to keep it away from the O2 sensor. Prior to that, I used a plastic tie-wrap to hold it away from the O2 wiring.

Once I get it figured out..I'll post up and let you know. Currently I've changed the valve out and have a switch on order with the dealer. Hoping to know something soon.

As I understand it the 171 code can be caused by lots of things... I just did the a lower & upper manifold replacement and I forgot to tighten the EGR tube at the EGR valve. I did tighten it at the manifold but it was only finger tight at the EGR valve it'* self. This would set off a 171 caused by reduced manifold vaccum. This happened mostly when the engine was cold...makes sense since once it got warm the EGR would start to inject gases into the manifold and reduce the vacuum loss. Might want to look in the area of the EGR

Look for any vaccum leaks, On my 96 with a 3.8 the PCV valve has a o-ring below the valve and a larger o-ring on the cap where you can lose manifold vaccum and set off a 171.

Spit

As far as that #6 Plug wire and O2 sensor issue, I just used the tie-wrap method and have been fine for about a year now.