If you shop at Amazon.com (for anything), use this link to support MyFordFreestyle.com!

U1900 on ABS, RCM, IC. Crazy CVT behavior.

Post Reply
someone972
New Member
Posts: 6
Joined: Sat Dec 28, 2019 10:38 pm

U1900 on ABS, RCM, IC. Crazy CVT behavior.

Post by someone972 » Fri Jan 03, 2020 8:30 pm

Hi all, was on a test drive with my rebuilt CVT. Was going slow in stop and go traffic and suddenly the belt slips (RPM go up), and then stuff starts getting crazy. Traction control light starts turning on and off on the cluster, wrench light turning on and off. CVT starts bucking and banging. Turned it off and back on and it worked better, although it still has a bit of a "pop" when starting off at slow speeds which may be mild chain slip. Pulled codes expecting a TCM code, but all I have is a U1900-20 in the ABS, U1900-A0 on the RCM, and U1900-20 on the IC. FORScan lists these as CAN bus communication fault codes. No codes stored in the TCM. So my question now is whether the transmission is the problem or if I just happened to have some crazy module which caused everything else to go nuts? Any ideas on what's going on?

someone972
New Member
Posts: 6
Joined: Sat Dec 28, 2019 10:38 pm

Re: U1900 on ABS, RCM, IC. Crazy CVT behavior.

Post by someone972 » Sat Jan 04, 2020 6:01 pm

Update: Seems like there may be something wrong with the TCM. Scan tool periodically disconnects from data-logging on that module. Occasionally it will error out reading the codes from the module. Tried seeing if wiggling the wires anywhere would consistently make it fail but can't get it to fail consistently. Unplugging the connector at the transmission and plugging it back in gets it to read the codes again, even without doing key-off. What's everyone think, am I looking at a failing TCM or could it be a wiring issue?

someone972
New Member
Posts: 6
Joined: Sat Dec 28, 2019 10:38 pm

Re: U1900 on ABS, RCM, IC. Crazy CVT behavior.

Post by someone972 » Mon Jan 06, 2020 8:03 pm

Alright, another update. I went and unplugged the ABS, RCM, IC, PAM, and DEM. No change in the behavior, still fails during data logging the TCM within 3 minutes. Got another TCM from the junk yard, exhibits the same behavior (although it's a junkyard TCM so no telling if it has the same fault or not). Plugged in another wire harness to the TCM from the plug under the battery, same behavior. Not sure where to go from here. Maybe I need to find someone with a known-good freestyle that I can attempt to data-log with my setup, and see if it has the same behavior and I'm chasing a red-herring.

someone972
New Member
Posts: 6
Joined: Sat Dec 28, 2019 10:38 pm

Re: U1900 on ABS, RCM, IC. Crazy CVT behavior.

Post by someone972 » Fri Jan 17, 2020 9:19 pm

So here's what I hope is the final update on this. Turns out my battery was failing in a rare way that I haven't experienced before. It appears it was intermittently going high resistance and dropping out. When it wasn't doing that, it was still reading full voltage, and cranked the car just fine. Started suspecting the battery but it still tested good, until one morning when I tried to start the car in super cold weather and was treated to a rapid relay clicking nightmare. Ohms on the battery kept going between open circuit and zero, and battery tester confirmed it was knackered. Replaced it, and haven't had the slipping issue since.

So my best guess is that the battery was intermittently dropping out, and while the alternator was probably enough to keep the car running, the electronic modules probably did not like it and reset or got crazy readings. For the record, my scan tool still disconnects when data-logging the TCM, but I'm suspecting that's a software or hardware issue on the scan-tool end at this point.

Post Reply