check engine light
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New User
Joined: Jan 2004
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From: Minnesota
check engine light
I need some help. My wife says there is no help for me but that's another story. The check engine light has come on in my 94 Bronco 5.8L with 121,000 miles on it. Comes on as soon the engine warms up. Pulled the code and I get 172 with or without the engine running. ( O2 sensor- running lean. ) That's it. The engine runs like a top. I try to stay ahead of the game with preventive maintainance. No change in mileage that I can tell. O2 sensor was replaced about 10,000 miles ago with a Bosch unit from NAPA. Wondering if anybody out there has the sure cure before I bring it to the shop and whip out the credit card. It's very frustrating as it runs and drives fine. Any ideas????? I'm not trying to be redundant as check engine light issues have been posted many times before but most of those seem to have driveability issues. Not me. Thanks for surfing my post.
Elder User
Joined: Dec 2002
Posts: 649
Likes: 1
From: Monterey bay area
Well since I installed the motorcraft O2 sensor on mine and I don't have thecheck light on...I would say that the Bosch O2 sensor operates on different parameters and is causing the code/light to activate.
have you tried erasing the code from the ECU memory?
perform a search here lots of info on this
have you tried erasing the code from the ECU memory?
perform a search here lots of info on this
Senior User
Joined: Dec 2003
Posts: 404
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From: Groton, CT
Get under the truck and look at the O2 Sensor wires. I had the same thing happen to me about 5000 miles after replacing my passenger side O2 sensor. Discovered that I had not adequately secured the wire (like a dumba#@) and it had melted and grounded out to the header.
Second possibility, did use use lube/sealer on the O2 sensor threads. Emission system is very sensitive to the introduction of foreign chemicals to the exhaust. Permatex UltraCopper is about the only one you can use without risk of fouling the system. (use very sparingly)
Wife is CT Emissions Specialist and they see that one a lot. People goop antiseize on O2 sensors then cannot understand why they failed after only a few thousand miles.
Good Luck and hope this helps.
Tom H.
Second possibility, did use use lube/sealer on the O2 sensor threads. Emission system is very sensitive to the introduction of foreign chemicals to the exhaust. Permatex UltraCopper is about the only one you can use without risk of fouling the system. (use very sparingly)
Wife is CT Emissions Specialist and they see that one a lot. People goop antiseize on O2 sensors then cannot understand why they failed after only a few thousand miles.
Good Luck and hope this helps.
Tom H.
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New User
Joined: Jan 2004
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From: Minnesota
Thanks guys for the info. Yep, I erased the code and it came right back. I'll take a look at the wires and see if something is goofy there. I used the antiseize that came with the sensor and was very careful not to goop it on but I imagine it wouldn't take much to screw it up. If all looks good, the Motorcraft sensor might be worth doing and I can go from there. If it comes on after that, then I may need more help. Thanks again!
Fleet Mechanic
Joined: Aug 2001
Posts: 1,526
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From: Round Rock, TX
I doubt that there is a problem with your sensor, although it is possible. I'd be looking for vacuum leaks and disconnected harnesses right now. Check vacuum connections and follow the lines to make sure that they haven't rotted/burned through anywhere. A good visual inspection is your start.
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New User
Joined: Jan 2004
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From: Minnesota
Checked with the Ford dealer, $106 for a Motorcraft 02 sensor. I think I will be crawling around under the hood a little more before I spend any money. Is there any danger in continuing to drive it with the 02 sensor sensing a lean condition?? I know it's not good but I gotta get to work somehow or my wife will divorce me. 
New User
Joined: Jan 2004
Posts: 5
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From: Georgia
Hey, go down to autozone and get an Actron code puller. It comes with a book and is a piece of cake. It will also clear your old codes if you want to start fresh without disconnecting your battery. Mine was $29 + tax.
Steve
Steve
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New User
Joined: Jan 2004
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From: NW Ohio
My 1989 f250 5.0L does the same thing. The dealership could not find anything wrong. After it warms up it flashes a few times, stops, and repeats over and over. It may be a glitch in the computer. If you find anything else out please let me know!!!
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New User
Joined: Jan 2004
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From: Minnesota
Hey, just an update on this thread. I think I have solved the problem. I thought I would change the O2 sensor just in case the one I put in 15000 miles earlier went bad. While I was under there, I figured I'd go ahead a throw a new fuel filter in even though I had replaced it within the last 15000 miles. Come to find out that the old fuel filter was completely plugged! 
Thought those should last longer than that but I guess not.
Anyway, no more check engine light.
The old O2 sensor was very carboned up so probably not bad that I replaced it. Thanks to all who responded or viewed my post.
Thought those should last longer than that but I guess not.
Anyway, no more check engine light.
The old O2 sensor was very carboned up so probably not bad that I replaced it. Thanks to all who responded or viewed my post.
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