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Does check engine light necessarily correspond to a fault code? 700 1991

posted by  Big Website on  Wed Jun 12 10:58 CST 2019
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Hi everyone,

My 91 740 base w regina motor has a check engine light. I read codes from obd port 2 and 6; one was all clear, the other gave me the codes 122, (signal missing from air temp sensor) and 233 (signal missing from iac valve).

The thing is, according to the site I went to to translate the codes, neither of them are supposed to set off a check engine light. Does anyone know whether either of these issues will set off the light?

I removed and cleaned the iac valve yesterday which shut off the engine light for 10 or so minutes before it came back on. I thought removing the negative clamp from the battery may have reset the codes so i removed and replaced it again today, but the engine light and code were there immediately upon startup.

Im also confused as to why my iac valve would be faulty because my idle is perfect. It could be an electrical issue with the plug on the valve.

I just want to know whether or not the engine light is the iac valve or something serious so i know whether to drive it.

Thanks!








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    Does check engine light necessarily correspond to a fault code? 700 1991

    posted by  maplebones on  Wed Jun 12 11:35 CST 2019
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    last visit: Thu Oct 23 22:53 CST 2014
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    Hi,

    I'm not familiar with the 740 or regina, but the 240 has a similar self diagnostic reader.

    Using the Diagnostic Control Function 3 and test lead in socket 2, push the button down 3 times for between 1 and 3 seconds. This will cycle the injectors, the IAC valve and cold start valve if you have one. Hold the IAC while it's testing and you should feel it click on and off.

    It could be the ECU is having a seniors moment. I wouldn't hesitate to drive it if it's operating normally until I could sort it out. Half the people in my state are driving with their CEL on these days.

    regards, Peter

    edit: Art's post wasn't there when I began typing my 3 words a minute. To be clear, he understands these thing while I do not








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      Does check engine light necessarily correspond to a fault code? 700 1991

      posted by  Big Website on  Wed Jun 12 16:34 CST 2019
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      im not quite sure how this posting system works yet so i dont know if you read my reply to Art, but you were both right about it being electronic. I cleaned the cable and the light is gone. Thanks!








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    Does check engine light necessarily correspond to a fault code? 700 1991

    uid 27's pic
    posted by  Art Benstein on  Wed Jun 12 11:30 CST 2019
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    last visit: Fri Oct 17 20:10 CST 2014
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    Dear Big Website,

    Saw your post last week on TB. We've seen several discrepancies between the DTC behavior listed in the various charts for MIL set, but the larger explanation might lie in what can happen to aging electronics in an aging automotive environment. IOW, EPA-required diagnostics (OBD-1) may not be following the same logic proposed by the designers after moisture incursion, corroded connections, and 30 years of skilled maintenance.

    First step is to know postively which box, the Rex or the Regina set your MIL. Unplug each to eliminate. While you're doing that, check to see the pins show no evidence of water damage.


    --
    Art Benstein near Baltimore

    “The only true wisdom is in knowing you know nothing.” -Socrates








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      Does check engine light necessarily correspond to a fault code? 700 1991

      posted by  Big Website on  Wed Jun 12 16:30 CST 2019
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      Thanks for your help!

      You were both right, it was electronic. I scraped and air dusted each end of the iac valve cable and the engine light is gone.

      If you wouldn't mind though Art, i'd like to know how i'd go about disconnecting the Rex and Regina boxes for the sake of education. I'm a novice and don't know what you mean. The ignition coil boxes on top of the struts? From my recollection they both look the same and i was under the impression they were 2 of the same thing. How can i tell which is which







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