CAT 3126b ECM Replacement

[John Demartini]

Good afternoon.  We have a 2000 Patriot with CAT 3126b.  I am currently dealing with a no start issue following sending my ECM to a "rebuilder".  The rebuilder sent it back to me stating there was no issues, promising a refund.  I sent it away because of recent failure of cruise control and tachometer.  Also, my PAC brake has never worked. 

Following reinstallation of the ECM, I now have no CEL bulb check cycle, no engine warming cycle and of course a no start.  Checking power and grounds to the ECM, both switched and un-switched, which have not revealed any issues.  Reading earlier post in Tech Support have given me some good direction to follow.  However, I suspect that with the lack of communication concerns, CEL and Warming cycles, I suspect that I will end up getting an ECM replacement.  I brought the ECM to a local CAT dealer, had it checked by their truck division, and they said they saw no issues.  I discussed getting a replacement unit and the discussion got very involved quickly with having to gather information on the differential, trans, injection pulse cycles etc...   My question:  is replacing an ECM for this CAT 3126b that involved?  I have the ECM Serial number and Personality Module number/release date.  Has anyone that had one replaced can give me some advice on this?

Thank you in advance for any suggestions.

[Steve Huber Co-Admin]

John,
With all due respect, it seems to me that you are chasing an ECM problem that doesn't exist. In an earlier post you stated that the Silverleaf was reading RPM correctly but the dash gauge was not. Since both get the RPM signal from the ECM, it would seem to say the ECM output was OK and your issue is elsewhere. It's also very doubtful the Cruise Control and PAC brake issues are ECM caused.You then sent the ECM to a rebuilder who said it was OK (did he do anything other that test it). You then took it to a truck shop who said it was OK. So why are you chasing the ECM?? From what you've posted, it certainly seems to be OK!
If this all started with a "no start" issue, I suggest you post the symptoms and what diagnosis you've done so members can possibly provide some advice. No start is normally a fairly straight forward issue to resolve. Otherwise  IMHO you will end up with more issues and lot less $ in your pocket.
Steve

[Carl Boger]

John,

I don't think your ECM is you problem either.  As for the no start try unplugging and cleaning your main harness connection in the front bay under the drivers seat.  I would also check all of your grounds and fuses including the fuses behind the batteries.  If two sources indicated your ecm was working I would believe them.  Hopefully this will be helpful.

[John Demartini]

Thank you both for the responses.  My no start issues only occurred after I got the ECM back from the rebuilder, also I get no information on the silverleaf during cranking.  Prior to removing the ecm and reinstalling, it always started immediately.  I will certainly check the connector under the driver's seat, but maybe I'm just chasing a fuel delivery issue at this point.  Thanks, again, and I'll let you know how I progress.

[Eric Maclean Co-Admin]

John
At this point I'd think you should recheck the connectors on the ECM to make sure you haven't got any bent pins and using a scan tool establish wheather or not you have communication , as you say it would start before the ECM was removed it could be a fault induced by the removal of the ECM  as you said you  could be just looking at a fuel issue.
As Carl mentioned if you have a working ECM and don't seem to have any related dash lights the problem may be in the large harness connector in or behind the front run bay cabinet .

Hope this helps
Eric

[John Demartini]

Good morning:  Thank you all for feedback and input.  As it turns out, the vehicle, or machine harness connector on the ECM was not seating completely due to poor thread condition with the hold down bolt.  Once I realized this, I was able to fully seat the connector and restart the engine.

I continue to have Tachometer function issue, cruise control not setting and inoperable PAC brake.  Now that I can communicate again with the engine ECM, I hope to make more progress.

Thank you all for your input and advise.

[Steve Huber Co-Admin]

John,
If the PAC brake is not working it very well could be causing the cruise control to be non-functional so suggest you focus on the PAC brake before addressing the CC.
Steve