I’ve got a 2012 Expedition with about 190,000 miles. Just came back from a long family road trip to Montana for some off-roading. On the way back to Nevada, I started noticing some weird stuff—like a slight shudder and a tiny dip in power that was on and off. About 15 minutes after that, the check engine light popped on.
I ran the codes using my code reader and got U0100 (ECM/PCM communication loss) and U0101 (TCM communication loss). I’m guessing it could be a wiring issue since the roads were super rough, or maybe I need a new ECM/PCM altogether.
I’m decent with fixing things at home, thanks to my dad and YouTube, but I don’t have the tools to run a full wiring diagnostic. I’ve checked all visible connections, cleaned up the battery terminals, and tested the alternator and battery, which all seem fine.
Before I go replacing the ECM/PCM (which sounds like a hassle), is there anything else I should check out? Or should I just bite the bullet and take it to a pro? Would love to get this figured out myself if possible—this truck is my baby. Any advice is appreciated.
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It might just be the wiring. I had the same U0100 code on my '09, and it was just a loose wiring harness. If it’s not wiring, then yeah, might be the ECM/PCM.
I’d suggest checking all your grounds before replacing anything expensive. Could be a ground wire that’s corroded.
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Thanks for that, I didn’t even think to check the grounds. I’ll go back and look over those.
If it’s the ECM/PCM, try to reflash it first. Sometimes the software gets wonky. If you know someone with a scan tool that can handle reflashing, it might save you some cash and effort.
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I tried reflashing on mine when it started throwing codes, and it worked… for about a month. I ended up replacing the ECM anyway. So, if it does end up being the ECM, just prepare for that as a possibility. Better to do it once and be done.
Since one of those codes is for the transmission control module (TCM), maybe look at your transmission wiring or the TCM itself. Just check before assuming it’s the ECM/PCM and it’s just a transmission issue.
Another cent, battery health can also be sneaky. Even though you said your battery tested fine, a failing battery might throw up random communication codes.
That’s something I hadn’t thought about. I’ve had zero transmission issues, but I’ll give that a look too. It was weird how the shudder came on right before the check engine light.