I have a 1998 F150 XL, 4.2L, with 205K on it. The other day I got a PO174 code which bank 2 running lean. This popped up after my wife went through a ditch to avoid an accident. When using my Innova scan tool to read the code and clear it, the next time I went to start the truck the battery indicator light came on. I checked the voltage in the battery and put it on a charge but today the truck died after my wife drove it around town and I had to jump it off to get it home. I had only an hour to get the battery and alternator out and get them to town to get them checked at the auto parts store before they closed. The guy there said his load tester told him that the battery needed to be charged but there wasn't enough time (I read 12.1V on my DVM). He couldn't test the starter either because all of their connectors were bad. I decided to gamble $140 on a new alternator and installed it, put another charge on battery and installed it, and ran the truck for 10 miles to let it relearn itself. The check engine and battery lights are off for now (battery is charging at 14V while running, a little less with the headlights and AC on) but I have a couple of questions. Could it be just a coicidence the alternator failed afterward or can incorrectly using a scan tool harm the alternator if you have the key in the on position (not running) too long? And, as for my PO174 lean code which I realize several things can cause, if it's an O2 sensor and I replace it, is there any other procedure I need to perform involving the PCM or ECM? Thanks

P.S. That guy at the auto parts store with a national name I'm not going to name also gave me a serpentine belt which was way too short, AND told me to check the alternator in vehicle by disconnecting the positive battery cable! Must be a newbie. Don't think he needs to be giving out advice like that.

 

I think using a scan tool or leaving the key on while scanning will not harm the alternator. I think it is a coicidence.

I had a PO174 easy fix. once.. I took a can of carb cleaner and sprayed it in strategic locations around the vacumm hoses. The spray will pick up the idle if a vacuum leak is present. I found the big vacuum hose behind the throttle body was not pushed on all the way. It was just bumped up against the fitting. It was tough to reach but i pushed it back on and the code cleared. Just be carefull with the spray. Just a little squirt is all that is needed.

I have to admit. I have checked alternators quickly on the fly by disconnecting the battery terminal. Just did it a couple weeks ago on my wifes focus. Her car wouldn't start at the groceery store and i had to go rescue her. I jumped it to get it going and pulled the terminal. It kept running which told me the alternator was doing something and the battery was suspect. . I flew up to the store (they tested the battery being dead, FLAT, "0" NADA) and I replaced her battery in the parking lot. Adding $100 to the grocery bill.

I can't tell you how many times i got the wrong part from the auto parts stores. That is why i try to take the original with me every time, if i can.

 

The 174 code is not the OX sensor. Leave it alone.
The code is telling you by association, the intake has an air leak at some location. The sensor is detecting as excess oxygen in the exhaust.
This fault shifts the fuel tables out of limits to richen the fuel, 'setting' the code.
YOU NEVER run the motor with the battery cable disconnected.
It causes the alternator to run wide open at high voltage with no load to reference to.
The electronics will only take so high a voltage.
14 volts is the normal running level.
Good luck.

 

I believe the alternator was the culprit since the battery light is no longer lit. Took the old one to Napa to have tested and it seemed to be putting out 14V but the guy had to put a boost to it whereas a new one he put on the tester didn't require one. I guess 10 years was pretty good for the old one. As far as the PO174 code goes, I have a K&N air filter and suspected the wire in the MAF sensor was probably dirty. Hit it with a couple of shots of contact cleaner and haven't had the check engine light come back on yet. Hopefully that's all it was. Much easier than tracing a vacuum leak or fuel system problem! Thanks to the both of you.

 

just behind the throttle body on the bottom side their is a elbow. I found this to be rotten out completely on mine. A real PIA to get on and off for someone with big hands

 

LOL! I hear ya. I had to replace a cam position sensor located somewhere down under there on the front end and it was a pain in the butt. The thermostat isn't much easier.

 

I work for Oriellys, at my store, I am the only one that knows anything about vehicles.

 

I know it has been a while since I started this post but I thought I would give an update. After driving around four a year and a half with with the check engine light on due to a lean code, I found two spark plugs on that bank had loosened up a little. Found this out while I was changing the plugs and wires out after replacing the brake rotors and had the wheels off. After hooking the battery back up and driving for two days, the check engine light hasn't come on. All this time I had been looking at hoses, lines, and gaskets!

 

Loose plugs won't set a lean code.
If enough compression and combustion pressure escape by the threads it would be detected as a misfire. Known by the computer as slower rotation time for those cylinders.
Removing battery cleared 'all' the tables back to un-shifted state.
This causes the PCM to do all diagnostics from scratch.
If your lucky in some way the cause of the lean codes may be a small leak that eventually will shift the fuel tables rich again and set the lean codes.
Sounds funny the say that but that's how it works.
By rebooting the PCM, the diagnostics see the tables all good again until any shift out of limits over some time interval.
If the lean codes come back, keep us informed.
Good luck.