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Thread: cruise control speed sensor

  1. 17th November 2014, 09:51 PM #1
    Dannyroger
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    cruise control speed sensor

    G'day all
    There's heaps of info on dodgy cruise controls but I can't find an answer to this.
    Cruise hasn't worked for ages, except very occasionally when it does for a period of maybe 20 or 30 seconds or so then just drops out. Mostly, doesn't come back for weeks.
    I've confirmed that the hoses are all ok and don't leak, the pump works, the bellows thingy holds vacuum, the brake switch & valve work, the steering set/resume switches work, the main switch works. I've also pulled out the ECU and resoldered whatever looked like a possible dry joint. Still the damn thing refuses to cruise.
    Using the test posted here Cruise Control Fix - Land Rover Forums - Land Rover Enthusiast Forum, everything checks out except the speed sensor test.
    The speed sensor doesn't give me an increasing voltage with speed as it should. Instead it gives a pretty constant 8.5 volts when moving at any speed and 12 volts or occasionally 0 volts when stationary. So seems reasonable to assume the speed sensor is dodgy, except the speedo - which I believe works off the same sensor - seems to work fine.
    Anybody have an idea?
    Thanks
    Tim

    98 D1v8 LPG
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  2. 17th November 2014, 10:56 PM #2
    dick180641
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    Mine, an AUTRON (Melb, Vic) gets its speed signal from the alternator not as an increasing voltage but a series of PULSES that vary in frequency as the speed increases.
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  3. 18th November 2014, 08:06 AM #3
    Dannyroger
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    What a great answer. I hadn't understood that it wasn't a slowly increasing voltage. The ECU swap with the p38/d2 version will be my definite next move. many thanks to Dick 180651. I'll report back when done.
    Last edited by incisor; 25th November 2014 at 05:41 AM.
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  4. 18th November 2014, 06:49 PM #4
    ROAMER_AUS
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    Quote Originally Posted by dick180641 View Post
    Mine, an AUTRON (Melb, Vic) gets its speed signal from the alternator not as an increasing voltage but a series of PULSES that vary in frequency as the speed increases.
    You get RPM signal from alternator, not speed. Speed signal you get either from gearbox or transfer case in general.
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  5. 18th November 2014, 06:52 PM #5
    ROAMER_AUS
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    I'm not sure about Land Rover of your vintage, but there are systems where cruise control works by ECU converting pulses from speed sensor to constant voltage level and then sends it to cruise control computer. But this is only in embedded factory installed cruise controls.
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  6. 24th November 2014, 05:37 PM #6
    rustydisco1
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    I too had a lot of trouble with mine, turned out the cruise control module was where the issue lied. I scoured over it twice before finding that the CRYSTAL had a very small dry joint. Small device, metal can close to the big IC (chip) from memory. It's part of the oscillator circuit and would be involved in clock pulse generation-very important for any digital microprocessor. The cruise module was made by Hella for Land rover IIRC. Assuming yours would be the same part.
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  7. 4th December 2014, 07:27 AM #7
    Dannyroger
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    UPDATE - a local LR specialist lent me two ECU's - he said both tested and definitely ok - but neither fixed my issues so I figure most likely not ECU after all. So I got back into my truck and drove away on a hot day ... and the cruise worked! Have now decided that it will often work when engine temp or engine bay is quite hot so maybe a wire or connection that expands with temp ....?
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  8. 4th December 2014, 12:23 PM #8
    Tombie Guest
    Have you tested the pump under the P/S headlight area?
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  9. 5th December 2014, 07:48 AM #9
    Dannyroger
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    Yes the pump runs and pulls in the bellows thing. Also have taken out the pump and checked vacuum hose connections and electrical. But I haven't done what I've read about which is running water through it to clean it out - not too confident with that idea.
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