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Old 07-13-2018, 09:19 AM   #1
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ECM problems

I went to get my Tropi-cal 330 CAT (3126B) Freightliner chassis after sitting for a month and it wouldn't start. No communication with ECM. Had all the correct powers and grounds so I replaced the ECM. Now it starts and runs fine except the odometer reads 000000 (speedometer reads fine), oil gauge reads 0 and the light is on (checked with mechanical gauge and it read 65psi cold at idle), and the low air buzzer is on. I contacted CAT and they said Freightliner has use their diagnostics to set those things. Does this sound right? Any help would be greatly appreciated! Thanks
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Old 07-13-2018, 12:33 PM   #2
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Odometer readings are commonly stored in non-volatile memory. The memory on GM cars was stored in the instrument cluster on many vehicles. When a portion of the cluster failed, the entire cluster was replaced. It was necessary for the dealer to program the odometer reading into the new cluster. ECMs, PCMs and TCMs have calibration data that varies based upon the sensors and loads the controller was connected to. My last TCM design was used on nearly 30 different models. The different calibrations were programmed into the modules before they were installed in the vehicles. For new vehicles, calibration was done on our assembly line. The controller part number drawing specified the firmware and calibration.

Based upon my experience with automotive, I would think they likely are steering you straight. They don’t expect end users to diagnose and replace an ECM. Anyone doing that is expected to have the required tools. I couldn’t go to a surplus yard and pull an identical module off of a Buick and put it in my Chevy because I do not have access to the proper calibration file and programming tool. Having designed the security algorithm for the module’s boot code, I know that if I tried to reprogram the memory without knowing the checksum of what was currently in there, the programming code in the BOOTROM would erase a vital part of the firmware. Then it wouldn’t even work on the Buick until totally reprogrammed. We didn’t want “tuners” to be able to reverse engineer the firmware.
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Old 07-14-2018, 06:33 AM   #3
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The RV was in a location where it was not accessible to a mobile tech and not able to be towed. I needed to at least get it running and moved to a location where it could be worked on. I was in contact with a CAT tech via computer and did basic “field tests” that could be done without CAT specific diagnostic tools. These tests indicated that it was highly probable the ECM was bad. The tach and all gauges except fuel were dead and the odometer read 888888.8. I purchased a CAT ECM through Freightliner and had it flashed using VIN and CAT engine ser.#. Now it runs and everything is good except what I mentioned. After contacting CAT they told me the mileage was entered into the ECM but only Freightliner could reset the dash.
I’m not a shade tree mechanic that just went to the junkyard and grabbed an ECM and slapped it in. I have over 50 years in the automotive field and was just asking for a little help in something I admit I am not very familiar with. After running my own shop for over 30 years I don’t exactly trust dealerships 100%.
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Old 07-14-2018, 10:14 PM   #4
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As it turned out, you got most of the job done properly and likely saved yourself some money. The remaining portion amounts to changing the contents of controller memory. Freightliner service sounds like the best choice for that. Often, after market scan tools will not do everything that the high end OEM scan tools will do.

The company I worked for manufactured some of Cat’s ECMs. That was a different group. I had no involvement.

The electronic odometer in automobiles was designed to make it virtually impossible to “wind back” the odometer. One version set bits as the mileage increased in a type of memory that could not be erased. There were some legal requirements to satisfy.
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