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Discussion Starter · #1 ·
I have had an issue since getting my truck back in January of 2008, the Qualcomm reads on the home screen under STATUS: **BAD 2000**, and hitting the "help" button on the keyboard displays:
Comm. Unit self-test failure
Replace Comm. Unit
MCT system needs servicing
Technician: Refer to MCT Diagnostic Guide

The truck is a 2007 model year Freightliner Century S/T 100 inch double bunk sleeper with LSD fuel emissions truck with 14.0 liter Detroit Series-60 engine and Eaton RT-10 trans with 3:58 gears and 295/85/22.5 tires, like half of that matters.

Possibly something to do with the black box under the bunk?
Also the latest issue I have been having with this truck is my gauges failing at just about any time they please, moreover lately when parked but a few times in the past while moving, thus setting a Hard Braking Event when they drop out like they do.

Reading my dash display when this happens shows:
ENG ROAD SPEED
Bad 128 084 12
It has done this on several occasions since mid 2008.
This newest problem with the gauges failing includes primarily the tachometer, oil pressure, & water temp gauges.

And the very latest in my truck gremlins beginning about 2 weeks ago the dash display reads the following when checked after displaying a flashing "ALERT NO DATA LINK":
ENG Controller
OPEN 128a254 07

Would this have anything to do with too much junk stored in the sidebox on top of and behind and around the black box in there, because after I removed all that junk and wiggled the wires to make sure they were seated or attached solidly, everything worked fine.

I have been through several different Freightliner dealers for this very problem, gauges zeroing out and setting an HBE event, and nothing being done about it except some doofus in Maintenance telling me how to reset the fault codes myself, and not documenting it.

OH yeah, and the next time a tech in a Freightliner dealer asks if I want anything turned up for free, I'll tell him my top speed to 65 and 1800 rpm's 6th through 9th.
 

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I don't know a thing about Freightliners.. but if it'd coming up with things like " no data link " and "open".. seems like it's showing open circuits in the data link.. if wiggling some wires temporarily fixes it, seems like a likely cause
 

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Discussion Starter · #3 ·
I have a feeling there was only a loose wire or connector on the black box under the bunk, but this thing has been through 3 different dealers for this same problem, two of them messed around with wiring under the dash panels and the third replaced a couple fuses, and a burnt relay unit, but only one of them even checked for the problem at hand that caused the gauges to drop offline like they did. That dealer only worked on the under dash wiring too.

i'll keep an eye on it and report it to our company fleet maintenance manager if that fixed it or not.
 

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this is my field of expertise

the 128 in the code applies to mid 128=engine
the road speed code has to do with the sensor attached to the back of the transmission where road speed is read. Rite before the tranny yoke, check your wire connections there and if that isnt the problem you need a new sensor.

data link problems occur in these truck all the time. So you may need to go to the dealership to have this taken care of. but most data link problem could be due to a bad componet, such as you say you have problems with the dash reading proper the tach, speedo and so on. it maybe that you have a bad Icu which is the dash and it own computer.

couple of ??? get me the last 6 of the vin.
I have all the books on these codes if it is the detroit, get back with me soon
 

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are you talking about the box (if sitting in drivers seat on the right side of truck under bunk, do you have a apu unit or opti-idle system, theres no engine control under the bunk unless it has to one of the two things listed above, I cant tell you anything about the codes unless it connected to laptop, but I can tell you that it is in the ecu or engine control unit which is attached to side of engine block left side behind fuel pump.
 
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