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Code 172 after changing O2 sensors.

Discussion in 'Stock 1991 - 1994 Explorers' started by mechjames, June 15, 2010.

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    1. mechjames

      mechjames Elite Explorer

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      HEGO sensor circuit indicates system lean (right side)


      I did reset the computer before I changed the o2 sensors. I thought it might be a good thing to do because i'm approaching 300,000 km and i'm unsure if they have been done in the past, and the concensus on here is that it seems to reduce mileage and power and not throw a CEL, because the EEC-IV has too much tolerance in O2 sensor readings, or the sensors just get lazy.

      I left the battery unplugged the night before I changed them. All seems well and it drives well but it throws a Code 172 a few minutes after driving. CEL seems to come and go as you're driving at first, but after that first few minutes when it comes on, it seems to stay on now.

      No KOEO off codes.

      Do I have a dud o2 sensor? Or is it just detecting a lean condition on the passenger's side? It seems to drive really great, but I won't know if i'm saving gas until I fill up the tank.
       
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    3. BrooklynBay

      BrooklynBay Staff Member Moderator Elite Explorer

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    4. mechjames

      mechjames Elite Explorer

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      Will check in the morning. Wiring from the connector to the harnesses were fine when I changed it.

      I'm assuming you mean the wires that run from the connector to the sensor itself.

      I don't think that the wires would have shorted so quick, because even on my first test drive, the CEL came on pretty quick. I will check it tomorrow.

      I didn't have a CEL before doing the O2's.
       
    5. rhauf

      rhauf Well-Known Member

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      make sure the connectors, where the o2 sensors plug in are making a good connection. sometimes they get corroded and don't connect well. plug them in and out a few times, use dielectric grease etc.
       
    6. TedJ

      TedJ Active Member

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      What brand sensor did you use?

      Try putting the original back in and see what happens. After all the pre-broken for my inconvenience parts I have gotten I would not be surprised if it was defective or something.
       
    7. mechjames

      mechjames Elite Explorer

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      Bosch Premium Direct Fit. Bosch supposidely makes the OEM sensors for Ford. They looked damn near identical.
       
    8. Reejerey

      Reejerey Active Member

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      possibly an exhaust leak in around the o2 sensor
       
    9. TedJ

      TedJ Active Member

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      Obviously check for an exhaust leak.....

      Bosch should be good, but it's hard not to suspect the replacement part if you have a problem you didn't before installing it. Try swapping them side for side or with the old one. If the code changes to one for the other side or goes away with the old one back in, go and complain that it is a dud.
       
    10. mechjames

      mechjames Elite Explorer

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      I do have a tiny exhaust leak, but it's downstream of the O2 sensor. I had to cut the Y pipe 2 years ago to get the transmission out and welded it back together. Just a tiny little tick, but it's not before the o2 sensor, it's after.

      I will just go and exchange it, the parts store is good to me. It wouldn't be worth my time to switch the sides, it's hard enough trying to unplug and plug it back in behind the engine.

      If it still shows a code with a new sensor, then i'll switch sides and see if the code follows.
       

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