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What does differential mag pulse generator feed: ABS+Speedo+Odo+Cruise?

posted by  someone claiming to be io333 on  Sat Mar 27 15:25 CST 2004 [RELATED]

Hi all. I'm still trying to figure out what my speedo and odo are dead.

I have some questions to help me narrow down possibilities. Does the pulse generator in the differential feed:

1. ABS for rear wheels?

2. Cruise control *directly*, or does the signal get modified before going into the CC computer?


The reason I ask, is because I don't understand why the pulse generator, or the wiring from it might be bad, when my ABS system is functioning perfectly, and has not turned on the dash warning light. Is it possible that there is still sufficient pulse to let the ABS think that things are OK, but it is still not strong enough to make the speedometer and odometer run? Also, my Odo started working intermittently for a while, and then died completely, before the speedo died, or stuck constantly at 45mph. Is this consistent with a dying pulse generator?

I'm pulling the differential cover off monday to clean off the generator to see if that helps. Should I just replace the thing while I'm at it? How much does a new pulse generator cost? Is replacement procedure obvious and simple, or do I have to measure & align stuff?








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    What does differential mag pulse generator feed: ABS+Speedo+Odo+Cruise?

    posted by  john sargent on  Sat Mar 27 17:30 CST 2004
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    last visit: Wed Oct 22 09:07 CST 2014
    [RELATED]

    For 700/900 series, the rear pulse wheel supplies one signal to the ABS system for both rear wheels. This same signal goes straight to the speedometer for 1989 and later cars (at least I think it does). For 1987 and 1988 cars this signal goes to an ABS signal convertor and then to the speedometer. The speedometer has an output terminal for the cruise control.

    If the ABS works, the signal is fine.
    --
    john








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    What does differential mag pulse generator feed: ABS+Speedo+Odo+Cruise?

    posted by  porkface on  Sat Mar 27 15:49 CST 2004
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    last visit: Fri Oct 24 09:12 CST 2014
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    what kind of car? chuck.








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      What does differential mag pulse generator feed: ABS+Speedo+Odo+Cruise?

      posted by  someone claiming to be io333 on  Sun Mar 28 07:26 CST 2004 [RELATED]

      Oh, silly me, I forgot. 1992 740 (has same dash as the later 940 models)







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        What does differential mag pulse generator feed: ABS+Speedo+Odo+Cruise?

        posted by  porkface on  Sun Mar 28 09:31 CST 2004
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        last visit: Fri Oct 24 09:12 CST 2014
        [RELATED]

        then you are correct. the abs is driven by the speed sensor in the rear end. does the abs light come on with the key on? if so, and it goes out, then the speedo is dead. there's a splice that divides the signal from the sensor to the abs and speedo. do all the other gauges work? the power for the whole cluster is the blue/red wire that is 1 of the wires that plug into the speedo. i'd like to see an ac signal at the speedo connector first, but with the abs working right, the speedo is most likely the culprit. no ac signal, then you gotta trace it back. good luck, chuck.








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          What does differential mag pulse generator feed: ABS+Speedo+Odo+Cruise?

          posted by  someone claiming to be io333 on  Sun Mar 28 13:29 CST 2004 [RELATED]

          ABS light behaves as it should, therefore, speedo is dead, or the connection is bad after the splice. I spent $270 having this speedo and odo repaired, with no result. Thank you very much for your response. I'll send the speedo back out again, but before I do, do you know where exaclty the splice is? I want to be positive the wiring is OK at, and after the splice.








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            What does differential mag pulse generator feed: ABS+Speedo+Odo+Cruise?

            posted by  john sargent on  Sun Mar 28 14:02 CST 2004
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            last visit: Wed Oct 22 09:07 CST 2014
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            The splice is a the main wiring connector which is above the hood release. You need to tell us what model year car.
            --
            john








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              What does differential mag pulse generator feed: ABS+Speedo+Odo+Cruise? 700 1992

              posted by  someone claiming to be io333 on  Sun Mar 28 16:08 CST 2004 [RELATED]

              Oh my. This problem has been maddening. It's much worse than a typical electrical problem, because I need a o'scope to trace it out & I haven't had one laying around in 20 years. Hmmm... It's just occured to me this very second though that I *can* test continuity between the wire coming from the sensor and the speedo. (!) Thanks everyone for all the replies. I'll try lots of stuff this week, and start a new thread later on either explaining what the problem turned out to be, or asking more questions.








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            What does differential mag pulse generator feed: ABS+Speedo+Odo+Cruise?

            posted by  porkface on  Sun Mar 28 13:39 CST 2004
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            last visit: Fri Oct 24 09:12 CST 2014
            [RELATED]

            i knew you were gonna ask, sorry, i need a diagram. i'd look for an ac signal at the speedo first, before i'd send it back out. good luck, chuck.







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