Just had the "service engine light" come on. Went to Checker Auto parts for the them to download the codes. Only the Code PO171 came up. He said it was an O2 sensor. My question is the PO171 code specific to an O2 sensor? If so, is there way to diagnose what O2 sensor? I have a 5.4 liter, 99EB, with 103,000.

Bought a Bosch 02 sensor for the left bank prior to the cat, waiting for it to cool down before changing. Looks like I can remove the senor with at wrench from underneath. Any comments

 

I wasted a bunch of time on this a few months back. And changed the 02 sensors which didn't help any. After following dead ends from a certain other for truck site, I eventually came across this forum which has been sooo useful, and this good advice in a 2003 thread....

"Check vacuum hose rubber fittings from PCV valve to intake manifold. They soften and deteriorate and vacuum will pull a hole in them causing vacuum leak. The main one that leaks is at the rear of the intake behind the IAC valve near firewall. (real fun to get to). It is a 90 degree rubber elbow fitting. The elbow is two different sizes 3/8 one side by 5/8 or so on the other. Dealer item only. You can get the whole setup PCV to intake. Some models have one tube PCV to Intake rear. Others have a Y near PCV that forks off and goes to Plenum below throttle body. The parts are not listed correctly in the parts manuals but a good parts man can get you the right one you need."

 

P0171 refers to bank 1, which is the passenger side. The code is not specific as to which sensor, only bank 1. You should have two sensors for each converter. One in front of the converter and one after. The front and rear sensors are different and Ford uses different colored connectors for identification. You might want to check for a vacuum leak. A vacuum leak can also set a lean code.

 

very common issue ,. and lynnr is probably right as to what the problem is, it is well worth checking out. And a quick and cheap fix for this, is use an old rubber boot from a old stlye coil wire the ones with 90 degree bend. much better then the factory replacement.

 

Thanks Lynnr -- I found the vacuum tube that goes to the plenum had a whole in it. This is a funny design, from the "y" is a plastic tube then right before the plenum it changes to a vaccum tube. I removed the vaccum tube and sure enough it has a whole about a 1/4" in diameter right in middle looks pretty fatigued/soft and collapsed as well. Did not notice any leaks in the one behind the manifold. Unfortunately all the auto part stores are closed tonight I'll get to it first thing in the morning. Hopefully this will fix the fault.

One quick question what is the best way to reset the light? Can you reset the light by disconnecting the battery?

 

Glad it worked out. Coincidence - I found the answer on a Sunday evening as well. Now, I don't usually cheapskate on repairs, but 3 months later, the hole in the elbow on mine is still plugged with silicon sealer reinforced with duct tape....

 

Oh, I've read elsewhere in the forum that you can reset the light as you ask, but I use my trusty but limited $60 Harbor Freight code reader. Autozone would prob'ly zap it for you...

 

If no scanner..

To reset the computer only, locate the small auxillary fusebox under the hood. It is on the outside sidewall right where the it meets the firewall.

Open the fusebox and pull the 5A fuse closest to the front bumper. Wait 15 minutes (ignition must remain OFF) then reinstall.

Doing this keeps you from having to reset your clock and radio which are required when you disconnect your battery for 15 minutes.

Either works.

BTW, this shows the futility of allowing the idiots at AutoZone to perform diagnostics on your vehicle. They typically have no clue on how stuff works, they just sell parts based on the codes and hope they get lucky.

Steve

 

Thanks guys -- Well, I picked up 3/8" fuel hose about 3" long to replace the faulty vacuum line. Reset the computer, then drove around this morning so far no faults. I'll give it a couple of days if the fault doesn't return, I'll return the O2 sensor back to Checker.

projectSHO89 -- thanks. Your right its kinda hit miss at the auto parts store, the best advise is right here on this forum.

Lou