2015 Chevy Colorado
Replaced rack and pinion. Flashed all modules to latest calibration erased code and code U0420 will return key on engine off.
Hey Ron. I would (dynamically) verify power feeds and ground to the module before going any further. What was the reason for the steering rack replacement?
Powers, grounds, data lines. Triple check part number is correct for that model. What was original complaint. There is also 2 bulletins for that code to check engine harness for chafing, aND remove ebcm connector to check for water intrusion. Ive seen lots of ebcm connector issues on them
“U” codes have plagued cars since the earliest multi module vehicles over 20 years ago. I have run across this issue many times, and, the cure has been beyond logic many of those times. Start FIRST with a very good battery tester and make double sure that it isn't THAT simple. I cure a high percentage of these issues with a new battery! Also, eliminate high power and ground resistance by doing…
U code doesn't necessarily means communication issue and the code definition says invalid data that means the modules are communicating but ps module is sending wrong info . You didn't specify if you installed a new/reman/used rack so before going any further you have to make sure part # is correct for the truck . You also didn't say why the rack was replaced, was the code there before?
Hi Ron, You have a lot of good suggestions here. Did you follow the Flow chart for the code? There are TSB's involved as well. A “U” code is seldom a mechanical involved failure. Time to do some real electrical system diagnostics.
Did you perform all of the relearns? Steering angle and such?
Can you comm with the PSCM? Was a new module used (cannot put used in this as all GMs from 14 and later are Global A architecture, and used parts will not program successfully)? Causes errors in programming. If you can comm with it, and it was used, put a new rack in it. The invalid data comes from incomplete programming/calibration/set-up if you can talk to it.