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Old 05-28-2003, 12:41 PM   #1
bryan_johnson
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1994 SC2
Default Adjust new odometer to correct mileage on 94' SL

Hello,

I recently bought a 94' SL2. One of the small nuisances that came with it was that the odometer was broken. Fortunately I have a spare 94' SL2 parts car in my garage and swapped the clusters. My odometer, however, needs to be adjusted to the correct mileage(upward from 85k to 145k). The signal that moves the odometer is electronic, so what pins on the back of the cluster do I need to stimulate, and with what signal, to move the odometer. I assume it's some sort of square-wave signal that is speed dependent.

My Haynes manual has a rough wiring diagram, but I'm hoping someone with the *real* shop manual could tell me which color wire the signal goes to the odometer at the harness going into the instrument cluster, as well as the type of signal used.



Thanks,

Bryan J.

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Old 05-28-2003, 03:01 PM   #2
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Even though the signal is electronic, if it's like my 1993, the odo is in fact mechanical and works off the speedo... so you just pry away the lock gear, and you spin the mileage up... should be easy to spin it up, but should not be able to go back.

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Old 05-28-2003, 07:09 PM   #3
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As far as I know only the FACTORY can adjust an odometer...I will strongly caution you, that ANY attempt to alter the position of the odometer rollers "manually" WILL reveal "tamper" evident tabs that will permanantly "mark" the odometer as "tampered with" Better just to note the old and new odometer readings for future use should you decide to sell the car...or perhaps KEEP the old one in a box somewhere.

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Old 05-28-2003, 09:03 PM   #4
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Thats good advice from the Wolfman folks

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Old 05-30-2003, 02:02 AM   #5
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Well, I called around and the one place in town quoted me $75 to adjust the mileage on the odometer. Seeing as how I only paid a few hundred bucks for the car, I wound up tearing apart the broken one to see how it worked, then very carefully took apart the good unit and adjusted the mileage to match the old odometer. Everything appears okay thus far, and it took me less than an hour to remove it from the car, adjust it, and put it back in. Pretty simple as it turned out, now I can get it inspected without setting off bells and whistles everywhere. The old cluster wound up having a small red gear with two missing teeth, one of which was embedded in it's mating gear.

I didn't encounter anything that would indicate I was tampering with the odometer, no single use press-fit tabs or anything of that nature. There may be some special coating on the screws that is applied after assembly like my stereo equipment? You can also spin the odometer either way quite easily, which was a bit suprising and now I realize why they went to digital odometers....these are too easy to mess with.

Oh, I did find out how to trigger the speedo. It uses a 12Vpp square wave from the ECU. I measured roughly 16Hz/10mph. I ran the speedo on the old cluster way up to see what it would do. As it turns out, once you get over about an estimated 170mph, the speedo deflects back to about 90mph, then climbs again as you further increase "speed". It will do this over and over until you get to about 700mph, which is where I backed off :-)

If you back down the speed, the needle drops, then pegs just exactly in reverse of the pattern when the speed increases. This is useless info, but I thought it was interesting seeing as how I doubt anyone will get a saturn upto 700mph. The wierd part is that the odometer will only run as fast as the speedo, so once it pegs at 140mph of so, it won't turn any faster. The odometer appears to get some sort of differential signal from the speedo, it's basically 12V signal, but the +12V must alternate between two of the pins on the odometer motor for it to advance.

Well, hopefully that's the end of the odometer saga. I had to increase it by 60k, so just running it electronically would have taken weeks...of course I realized this as I was hooking up the pulse generator to the speedo input line...but better late than never I suppose....


Bryan

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Old 05-30-2003, 02:43 AM   #6
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If you could find a local shop that sells those gears (the one you found broken) or a machine shop that could make up 100 or so for a reasonable cost, you could get rich selling them to Saturn owners with broken Odometers. If memory serves the "tamper tales" are not "obvious" but exhibit BETWEEN the dial rollers somehow..although I cannot say "for sure" whether they exist in the unique Saturn Odo's or not, they are common to GM cars. In any event, glad to hear you got it fixed and had fun expirementing.

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Old 06-04-2003, 12:36 AM   #7
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I recently caught the odometer in my new DOHC instrument panel. I did it electronically using the parallel port on my computer, a couple of transistors, a couple of resistors and a 12V battery charger. Unfortunately I forgot to disconnect the motor from the driver that's built into the IP so I burned out the chip, fortunately I had one that got busted in shipping that I could take that chip out of. The absolute maximum speed the odometer motor is capable of running at is about 750mph, after that it starts studdering and gets slower. I can make a schematic and send the programs I found and the batch file I made if anyone's interested.

Jst playing around I hooked my dremel up in place of the motor on my broken one... The teeth on the gears broke and flew across the room, I think it was going like mach 70, so never drive faster than that, you'll break your odometer.

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