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Old 09-02-2022, 11:52 AM   #1
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Help Locating 2003 Thomas ECM

Does anyone know where the ECM is located on a 2003 Thomas flat nose? Or if there even is an ECM? I'm unsure if this is all mechanical or not.

Thank you.

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Old 09-02-2022, 12:00 PM   #2
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Originally Posted by Sasquatters View Post
Does anyone know where the ECM is located on a 2003 Thomas flat nose? Or if there even is an ECM? I'm unsure if this is all mechanical or not.

Thank you.
What drivetrain?
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Old 09-02-2022, 12:04 PM   #3
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What drivetrain?
Of course I left out the most important information

3126 with an Allison 2000
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Old 09-02-2022, 12:12 PM   #4
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Intake side of the block above the starter. Cummins and Cat typically attach the ECM to block. Mine is conveniently behind Fuel lines, compressor lines, Injector lines, and Fuel filter. I have to unhook it everytime i weld on the body.
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Old 09-02-2022, 12:42 PM   #5
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Intake side of the block above the starter. Cummins and Cat typically attach the ECM to block. Mine is conveniently behind Fuel lines, compressor lines, Injector lines, and Fuel filter. I have to unhook it everytime i weld on the body.
Thank you for that information. I am not mechanically inclined, but I'm working on it which is half of the point of this post. Would you mind telling me what the intake side is? Since we have a flat nose, and can only view the motor from underneath, or through the dog box, I don't have too much room to poke my big head around.
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Old 09-02-2022, 12:47 PM   #6
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Intake side is usually the "cold" side of the motor. Opposite of your turbo and exhaust manifold. Then they route the intake from the intercooler down to the other side of the block.


Now i have to ask.. What are you doing once you find your ECU? They typically dont need messed with unless your are replacing or welding.
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Old 09-02-2022, 12:51 PM   #7
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I am going to add a much needed cruse control module which require 3 or 4 pins to be connected via the ECM. I see you mentioned ECU. Just want to clarify we are indeed talking about the same thing.
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Old 09-08-2022, 02:26 PM   #8
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On my 04 Thomas with a Cat the ECM/ECU, yes it's the same thing, both the ECU and TCU are located under the floorboard attached to brackets at the outside left, just about under the drivers seat or slightly forward almost where your feet would be.
Maybe I'm a dummy but I've never unplugged either one for welding. I do have a big a$$ master switch at the batteries that I always switch off before welding. Does that do any good?
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Old 09-08-2022, 02:48 PM   #9
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On my 04 Thomas with a Cat the ECM/ECU, yes it's the same thing, both the ECU and TCU are located under the floorboard attached to brackets at the outside left, just about under the drivers seat or slightly forward almost where your feet would be.
Maybe I'm a dummy but I've never unplugged either one for welding. I do have a big a$$ master switch at the batteries that I always switch off before welding. Does that do any good?

At a Minimum, you want to disconnect both the battery hot and ground.


ECU circuits are somewhat sensitive to welding. 99/100 times there will be no issue leaving them all plugged in. I think where the issue usually lies is where there's a bad ground on the welding clamp and the electricity is "loose" in the bus body.


I have a ECM, TCM, and ABS controller. Each of them costs more that i bought my bus for, so i unplug all three. It does make it less convenient to quickly weld things on the fly. I usually batch a list of things to weld together so I'm not messing with those things all the time. Additionally i use jumper cables to ground my bus frame to a ground rod just in case i missed something. Im not usually this paranoid, but my manual mentions unplugging all three of these before welding, my ECM has already been replaced by the school district, and i have seen multiple videos where my motor or tranny had its computer wrecked after welding.
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Old 09-08-2022, 03:00 PM   #10
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+1 on disconnecting the battery.. and if you are adding pins to the connector.. be VERY careful and invest in the CORRECT TOOLS to work with your connectors for attaching the pins to the wires and poking the pins into the connector... I dont know the CAT specifically but ive known people to ruin allison TCM's by incorrectly inserting a wire and causing a short which blew the input pin and required replacing the module..
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Old 09-08-2022, 07:49 PM   #11
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Quote:
Originally Posted by 1dmpo View Post
On my 04 Thomas with a Cat the ECM/ECU, yes it's the same thing, both the ECU and TCU are located under the floorboard attached to brackets at the outside left, just about under the drivers seat or slightly forward almost where your feet would be.
Maybe I'm a dummy but I've never unplugged either one for welding. I do have a big a$$ master switch at the batteries that I always switch off before welding. Does that do any good?
Thanks. I have seen that under there but never needed to get into it until now.



Quote:
Originally Posted by cadillackid View Post
+1 on disconnecting the battery.. and if you are adding pins to the connector.. be VERY careful and invest in the CORRECT TOOLS to work with your connectors for attaching the pins to the wires and poking the pins into the connector... I dont know the CAT specifically but ive known people to ruin allison TCM's by incorrectly inserting a wire and causing a short which blew the input pin and required replacing the module..

The pins slide right into the connector. No tools required.
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Old 09-08-2022, 10:15 PM   #12
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Quote:
Originally Posted by fo4imtippin View Post
At a Minimum, you want to disconnect both the battery hot and ground.


ECU circuits are somewhat sensitive to welding. 99/100 times there will be no issue leaving them all plugged in. I think where the issue usually lies is where there's a bad ground on the welding clamp and the electricity is "loose" in the bus body.


I have a ECM, TCM, and ABS controller. Each of them costs more that i bought my bus for, so i unplug all three. It does make it less convenient to quickly weld things on the fly. I usually batch a list of things to weld together so I'm not messing with those things all the time. Additionally i use jumper cables to ground my bus frame to a ground rod just in case i missed something. Im not usually this paranoid, but my manual mentions unplugging all three of these before welding, my ECM has already been replaced by the school district, and i have seen multiple videos where my motor or tranny had its computer wrecked after welding.
Ok, Thanks. I've welded on two of my own buses and a couple for other people and all I've ever done is disconnect the batteries so the electronics were dead, guess to be completely safe we should unplug the boxes too.
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