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If you have an A1R do not try to test the voltmeters on dash. They are not voltmeters, they are indicators driven by CAN data from a ECM or ECU. Do you know where that unit is located in the truck??
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A1R Warning about gauges
- Thread starter m-35tom
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Ugh! Can bus.....
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Well some kind of data bus, the volt meters have microprocessors in them. To hard to just have a volt meter!!
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I can read these signals with my Picoscope if it is CANBUS. If there is no signal, the whole board typically gets replaced.
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In an A1R where does the signal come from?
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Cat ecm
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how do you know? do you have wiring for A1R?
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I have never looked at one on a military vehicle, but usually there is a central CPU and small cpu's in various aspects of its operation. Look for a box that is similar to the C7 or 3126's ECM. The box may be heavily shielded, if it is EMP proof. In a car with CANBUS, for example, the operation typically done be a relay is taken over by a small cpu's in each door, or truck, or whatever you want to control from the central cpu. It allows much greater flexibility in functions than just on off. If a board goes out, it's typically expensive. Typically the whole board is replaced since it is SMD.
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Cat can log into the ecm to make changes to match the speedo to the hs gears.
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Oh ok, so he is just trying to get the speedometer working. Thought he had a dead CPU board.
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NO, I was just saying that the VOLTMETERS on the dash were databus. A voltmeter!! WHY. So I can calibrate the voltmeter with the scan tool maybe?
But the idea of changing the speedo through the C7 engine ECU gets my attention since I am soon putting 3.07 diffs in and I have the CAT scan tool and ETM
And I plan to repair the voltmeter, it is just smd, no problem. That's what I do.
But the idea of changing the speedo through the C7 engine ECU gets my attention since I am soon putting 3.07 diffs in and I have the CAT scan tool and ETM
And I plan to repair the voltmeter, it is just smd, no problem. That's what I do.
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He asked how i know what controls the gage bus.
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So if the volt meters speaks CANBUS, then the whole system is CANBUS. Seems a bit overkill to canbus a volt meter, but it does not really surprise me. Now that I think of it, if a had a truck with an ECM, I might carry a pre-programmed spare. My experience with ECMs has been not great. Don't know anything about the CAT ones and reliability. SMD repair can be done with a heat gun and a microscope, as you know. No biggie, if you can trace the signal and find the bad part or look for burned parts on the board. Wonder why it died.
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This is correct. You can change the ratio via the ECM to make it read right.
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In reality is it not in the allison trans ECU?
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When I took my 3126 ECM in to CAT a year ago we walked through the settings. There's a field for the gear ratio that will change the speedometer. I'm setting up a CAT ET laptop to play with these things instead of paying for a tech's time. I bet there's more we can play with in there.