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Author Topic: Understanding the ECM on your engine your engine will not run without it  (Read 520 times)

Dave Atherton

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Many owners like to add various equipment to help understand what the engine is doing while running down the road.  While the intention is good, the outcome can sometimes be very bad (and expensive). Some of this added equipment is attached to the ECM Data Port, the same port used to connect the engine ECM to the CAT diagnostic equipment used to troubleshoot engine problems and supply upgrades if required. Often there are multiple devices connected that may include dash displays, trip recorders and transmission controls. Be aware that these devices may cause problems with the functioning of the ECM and disrupt communication with it. Many times I have attempted to connect the ET to the ECM and find the data communication channel disrupted, with the ECM not recognized, resulting in a ECM Comm failure on the diagnostic equipment.
The ECM data link is wired without fusing. There are different data links, a 6 pin named J-1708 and a 9 pin called J-1939 which provide engine data. The ECM has 1 switched and 3 unswitched 12v lines. Additionally it has 4 ground wires, running to different ECM pins.
If you connect a piece of after-market equipment, you must be sure it is wired the same as the data link. A good example of this is I found a case where the 12v unswitched lines were wired to ground in the after market equipment. The equipment’s directions stated just plug it into the data port and turn it on. The ECM failed.
Many companies build equipment that connects to the ECM data port and in most cases operate trouble free. However, trouble can arise when connecting multiple equipment, especially if the equipment is to be “hard wired” to the data port lines. J-1708 and J-1939 data link wiring is shielded twisted pair. This is to eliminate or greatly reduce cross talk and electrical interference from external sources that could disrupt ECM functions. If theses wires are cut, or otherwise damaged, they need to be replaced.
We often try to save $ by the DYI approach, but in cases like this, the downside can be very expensive.
Dave Atherton; Retired CAT Mechanic
« Last Edit: March 20, 2019, 07:57:57 PM by Steve Huber Co-Admin »

Pat Long

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Dave,    Is the Silverleaf system pretty much trouble free while communicating with the engines ECM.   Also, I have the J-1708 6 pin diagnostic plug and have the OtC Evo Genisys scanner with the Heavy Duty software installed and use this to diagnose anything beyond my Silverleaf system.  Have you heard any problems with the communication between the OTC system and Cat software during diagnostics?

Thank You for All your time and efforts,


Dave Atherton

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Pat, for any aftermarket product the SilverLeaf has its name and is well known in the motorhomes
market today. SliverLeaf is aware of using the Caterpillar data test to operate there equipment. The
Only thing I would suggest in purchase of aftermarket add on into a data test port is have the builder
which is SilverLeaf trained personal make the connection or install into Caterpillar system without
question. We as many have different levels of skills and not down grading that point but a factory
Technical person knows what to look for for correct pin wiring. Going to question number two, you
have another aftermarket product that takes over after SilverLeaf data stops and want to tie into
The Caterpillar data test port.  Now we are reaching and my answer would be no. I think my last post
Briefly explained the downside to all of ECM failure. To further explain there are several where the
Data test port in front has a aftermarket product installed, than another aftermarket system installed
to the rear Caterpillar test port. Let’s stop and weight all the cost savings, for whatever reasons
Than the what happen if factor,  when your down along side road and engine will not run. All in all,
many of us are not trained mechanics, your electronic engine built with all the system derate power
than shut down engine without anything added to there system. Than the thought process comes
Into play this aftermarket add on puts a code across screen ( 102-2 boost pressure sensor ) this
Is kinda cool now I have a problem but do you ? Understanding what kind of code active fault code,
logged event code or event code and last critical event code. These code readers do not break out
The type and nature of code on screen. In closing myself, the data test port is used for trained
People to diagnostic problems within there engine and make upgrades to your engines and it is
spelled out as such in technical information. You the owner can do or add anything you would like
It’s your engine. I hope I answered Pat your questions. Dave Atherton Retired Cat Mechanic

Jeff Fitzloff

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Dave, I have been looking at Bluefire as an option to see a much more inclusive display of the operations on our 2005 Beaver Santiam, from what I am reading here this may not be a goo idea?
2005 Santiam

Dave Atherton

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Jeff it is not my intention to rate as what person wants to buy. I’m just making you aware that
the data test port is not a household electrical connection to be used to power attachments. The
engine data cable sends a signal to Caterpillar and Cummins diagnostic test equipment depending
on which engine. Yes, this data test port has 12 volt power along with grounds that travel through
18 ga wire harness back to the engine ECM which sends signals to diagnostic test equipment reading
Perimeters off all electronic sensors within your electronic engine to troubleshoot and update ECM.
Going back on my first post on concern about ECM comm failure making people aware using builder
OEM diagnostic test equipment troubleshooting engine problems. Can not explain myself any more
clear at some point the engine needs to be left the way it was built and shipped. Remember it
is getting very costly at many service repair shops and many Caterpillar service shops do not make
service calls and many do not work on motorhomes. Dave Atherton Retired Cat Mechanic.

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