Odometer reads different when swapping instrument panel - Chevy Impala SS Forum
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post #1 of 11 (permalink) Old 05-21-2016, 02:59 PM Thread Starter
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Odometer reads different when swapping instrument panel

I have a 1995 Caprice wagon with a flickering speedo/odo. For whatever reason, I assumed the instrument panel somehow held the odometer miles. Looks like I was partially right. I have a 1996 9C1 doner car with 160963 miles and my 1995 wagon currently has 160947 miles. I was testing the doner IP in the 1995 and the odo reads the doner mileage with the ignition on (not started). When I start the car, it reads the 1995's milage (I assume from the ECM).

Is there any way to set the instrument panel's mileage to the ECMs? I know it's trivial but that's going to drive me nuts. Guess I can take a 16 mile drive to sync them up if there's no other way.

1995 Caprice Wagon
1996 Caprice 9C1
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post #2 of 11 (permalink) Old 05-21-2016, 05:36 PM
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Mileage is stored in the cluster, not the ECM. I have heard of ways to adjust the mileage on them, but I don't know the details.

Jonathan

96 Impala SS, DGGM, 2nd owner, 101k miles, #39736 of 41934, Build Date 22 November 1996
96 Caprice Civi L99, bought it new for my Uncle, recently re-acquired
92 Honda Accord 2 door, 353k miles, daily driver
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post #3 of 11 (permalink) Old 05-21-2016, 06:56 PM Thread Starter
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There has to be another mileage stored somewhere else besides the cluster since I turn the car on it reads 160963 but after I start it, it reads 160947. Not really a deal breaker but I'm curious as to why that is.
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post #4 of 11 (permalink) Old 05-21-2016, 09:11 PM
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?????????????????

Please do not take offense but I thought this was a late April fools post.
Go to Goldsswagon: (The link "A")

A

Load Instrument Cluster 94/95.
The speed pulse comes from the PCM (pin8) and goes to the vehicle speed input. This signal also goes to the cruise control, power steering, (RM) and the convince (chime) module. The important word is INPUT. It is a one way signal from the PCM that pulses 4000 pulses per mile to the other devices. If it did not work this way others like myself could not install aftermarket speedometers.

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post #5 of 11 (permalink) Old 05-22-2016, 04:42 PM Thread Starter
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Not talking about the speedo but the odometer. I looked over the wiring diagrams but there has so be something not listed that's feeding the ECM odometer reading to the cluster.

Made a video just to prove I'm lying.
https://www.youtube.com/watch?v=wEI_9b26nWg

Did some more digging and apparently this is not uncommon for the mileage to be stored in multiple places. Since there doesn't seem to be a way to set the cluster mileage easily to the ECM mileage, I'll roll with the original IP until it matches up. It's just 16 miles.

1995 Caprice Wagon
1996 Caprice 9C1
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post #6 of 11 (permalink) Old 05-25-2016, 05:16 PM
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The mileage on the 94-96 digital clusters is stored in the display/display attached board. I've repaired over 50 of these.No where else.
Winger why don't you simply have your cluster fixed?
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post #7 of 11 (permalink) Old 05-25-2016, 09:48 PM
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I always thought the mileage was only stored in the cluster and not the PCM, like others have said. Your video definitely makes me question that.

Are you positive that the mileages it is showing are the exact mileages of the donor car and the car that it's in? If so, it seems pretty obvious that these numbers are being stored someplace.
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post #8 of 11 (permalink) Old 05-26-2016, 10:30 AM
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Reality, Logic, Factory Service Manual

I own the 1994 FSM and have looked at the 96 FSM. The diagrams are also available on alldata, on goldsswagon.com, (many thanks for his great site), and in libraries. With the exception of the 96 Impala they seem the same.

I have found no "extra" wires in the two plugs to the cluster. I have had a oscilloscope on the Vss line and it's signal is one way and matches what many others have said about the pattern. I always take the connectors with the cluster and none have mystery wires. I have traced the circuit board between the speedometer chip and the cluster plugs. Everything matched my FSM. No one has ever reported extra wires connected to a stock PCM.

There are some good unused pins on the cluster. I think to meet European law they added a separate light for the parking brake warning and a light for the Hazard flasher. This forum has a long history (with gaps from the crash) but the general agreement is only speedometer repair places can change the odometer in the cluster. A internet search will show a few offering to "correct" the mileage of a cluster when they fix or replace the cluster. How can they do this if the mileage is stored "somewhere else".

For those who think the Odometer information is "somewhere else" than the speedometer chip on the cluster please supply diagrams, pictures and documentation.

I think the video is real. Of the many speedometer/odometer failures I have see my own first car would display two different odometer readings. I did not try to repair this one as I suspect a damaged "chip".

For the more common failures of dim outs and blank outs the forum has two repairs. See "1995 9C1 Intermittent Dash Display Fix" for both with great pictures and instructions.

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post #9 of 11 (permalink) Old 05-26-2016, 11:28 AM
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Binary Error?

Take a look at the two mileages in binary. The chance of two different car's mileages in binary or decimal being so close seems odd.


100111010010110011
100111010011000011

If you add 001 to 011 in binary you get 100. One bit error difference between
mileages.

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post #10 of 11 (permalink) Old 05-26-2016, 12:18 PM Thread Starter
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LOL! I hesitate to even mention my latest findings to this skeptical crowd. So the day after the experiment, I decide to reinstall the '95 IP and drive it from 160947 the 16 miles to match the '96 at 160963. I put in the '96 thinking it should now match but instead it still reads 160963 but 160947 when started.

I'm starting to think the odometer is faulty on the '96. I've turned off the car and it'll read a different mileage when the car is restarted. Trip shows I've driven 127 miles but according to the odometer, it reads 160999. I've yet to experiment with the '95 IP. Might have to resort to having the flicker issue fixed and see if they can get the trip working. Or maybe go Camaro IP.

1995 Caprice Wagon
1996 Caprice 9C1
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