1. Check engine light came on after purchase

    So I recently just bought a 94 YJ with a 4.0l straight 6 with 134k miles on it. When I test drove it there was no check engine light on but when I took it home the next day and washed it the engine light came on with error code 21 & 33. 33 had something to do with the AC which it doesn't even have and 21 was something with the O2 sensor. He told me he replaced one but not the other. Question is would it be out of line to ask him to cover the cost of having it fixed if it was a larger issue? I told him before I bought it that it needed to pass smog and be street legal which he has all the paperwork from the last smog checks dating back the last 4 years or is it something I have to eat?

  2. #2
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    Check engine light came on after purchase

    Yes ask.
    By disconnecting the battery for a few min will clear the codes. My guess is that is why it was being sold.

    O2 codes have many causes,
    Exhaust leak
    Cracked exhaust
    Intake leak
    Bad heater
    Shorted sensor
    Bad wiring
    Running lean or rich.
    Timing

    Start by checking the fuses. The O2 has a fused connection.
    Then by cleaning the battery terminals and connectors. Then clean the opposite ends. Be sure the battery is charged snd good condition. Bad connections snd weak battery will cause issues.
    Then check the wiring.
    What brand O2 sensor?

    Never look down on anyone unless you are helping them up - Jesse Jackson
    Last edited by JPNinPA; 03-02-2021 at 11:07 PM.
    "Never look down on anybody unless you're helping him up" - Jesse Jackson

  3. #3

    Re: Check engine light came on after purchase

    Ok I know the battery looks rough as well as the terminals and some wiring when I scanned it this is what the code said:

    Error code 21: 1. oxygen sensor stays at center ( no rich or lean signal detected when in closed loop ) ( cars 1983-95) (trucks/vans 1987-95) (jeeps 1993-95)

    2. Oxygen sensor shorted to voltage, signal too high (cars/trucks/vans 1990-95)

    3. Right or left bank, upstream or downstream oxygen sensor, stays at center ( no rich or lean signal detected when in closed loop) shorted to voltage, shorted to ground, slow response or heater failure (cars 1996-97) ( trucks/vans jeeps 1996-97)

  4. #4
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    Re: Check engine light came on after purchase

    Yep. Start with the wiring. Verify the make and PN if possible of the O2.
    Bad battery or connections result in odd CEL conditions.

    To tell which one. Unplug one wire connection. Reset the codes and verify what codes pop up. If 21 does not come back that is the O2 that needs replacing.
    Only use NTK sensors. They are OEM. Bosch often give weird results.


    Never look down on anyone unless you are helping them up - Jesse Jackson
    "Never look down on anybody unless you're helping him up" - Jesse Jackson

  5. #5

    Re: Check engine light came on after purchase

    Sweet, thank you I'll give that a go tomorrow!

  6. #6
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    Re: Check engine light came on after purchase

    Did you ask them to repair or what the issue is?

    Check your state laws on vehicle sales.


    Never look down on anyone unless you are helping them up - Jesse Jackson
    "Never look down on anybody unless you're helping him up" - Jesse Jackson

  7. #7

    Re: Check engine light came on after purchase

    Yes I contacted the seller and I took it to a shop this morning to have a diagnostics test ran on it and smog if they figure it out. Of course on the drive to the shop the light went off so I'm hoping they can still read the code that it was showing. I talked to them and told them about about how it went off in the way over there so we'll see what he says this afternoon.

  8. #8
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    Re: Check engine light came on after purchase

    Ok if it went on during a long highway drive. And a few short drives it turns off is not likely an o2 sensor issue but something else causing the fault.


    Never look down on anyone unless you are helping them up - Jesse Jackson
    "Never look down on anybody unless you're helping him up" - Jesse Jackson

  9. #9
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    Re: Check engine light came on after purchase

    FYI
    21 Upstream oxygen sensor response slower than minimum required switching frequency. Upstream oxygen sensor heating element circuit malfunction. Downstream oxygen sensor heating element circuit malfunction. Downstream oxygen sensor input voltage maintained above the normal operating range. Oxygen sensor voltage too low, tested after cold start. (Upstream or Downstream) Left oxygen sensor input voltage maintained above the normal operating temperature.


    Regards,
    JPNinPA

    Never look down on anybody unless you're helping them up. -Jesse Jackson
    "Never look down on anybody unless you're helping him up" - Jesse Jackson

  10. #10

    Re: Check engine light came on after purchase

    Ok so long back story but I'll try and keep it short. The light was off when I took it to the the shop and they diagnosed it and still found the o2 sensor fault. They wanted to charge the seller for $800 for the diagnosis, smog, o2 sensor and they said it should have a coolant flush and new thermostat, the previous owner was ****ed so I said take it to another shop and get a bid and have whoever check and smog it, he agreed. So he took it to a shop that a "family friend" owned and he said it passed "no problem" and said no check engine light was in so it was fine. The guy also said while I was on my way down there he talked with the guy before hand and said everything is paid and fine. I'm kind of a worst case mentality type person so in thinking I'm just wondering how hard it would be to have this " botched" and if I should get a second opinion before signing it over?

  11. #11
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    Check engine light came on after purchase

    what state are you in?

    Many states requiring smog testing check for CEL codes and that there is sufficient stored data. The stored data is to insure you are not clearing the code by disconnecting the battery.
    Also many smog shops and other mechanics will try to up sell you.

    And I take it the family friend mechanic was the sellers friend? . Come on... If you need it to pass smog then reduce the price by $1000 and you take care of it. If you sign off on it you bought a jeep you cannot drive without spending more..


    On the other hand find one for 1000 more that passes smog and buy that one.


    Regards,
    JPNinPA

    Never look down on anybody unless you're helping them up. -Jesse Jackson
    Last edited by JPNinPA; 03-05-2021 at 06:38 AM.
    "Never look down on anybody unless you're helping him up" - Jesse Jackson

  12. #12
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    Check engine light came on after purchase

    O2 sensor $25(NTK) -$100(mopar)
    CAT $305
    Manifold improved $150
    Down pipe $ 60
    Muffler $70
    Tail pipe $90

    1994 JEEP WRANGLER 4.0L L6 Exhaust & Emission Parts | RockAuto

    Regards,
    JPNinPA

    Never look down on anybody unless you're helping them up. -Jesse Jackson
    Last edited by JPNinPA; 03-05-2021 at 06:40 AM.
    "Never look down on anybody unless you're helping him up" - Jesse Jackson

  13. #13

    Re: Check engine light came on after purchase

    I'm in california and I know the other shop tried to upsell me on some if that stuff like the thermostat and flush. On the other hand I blew it because I paid him and have the jeep but I haven't signed anything over yet officially so I'm thinking I might go have it smogged on my dime somewhere else and explain my situation. Is there a way to look up the numbers that came back on my report and see if they match up at what a vehicle like this should be reading?

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