History: Was checking fuses (vehicle off) due to lane sensor warning not working, fuses were good. Went to start the car (2014 Mazda 6) and got the dashboard Christmas tree. Pulled the engine code U0121 lost comms with ABS module. Re-checked all fuses and their positions. Performed a hard battery reset (no help), performed a "hold trip/odometer TEST" reset (no help), tried to clear the code with my OBD-II scanner (did not work).

I guess it is possible that the ABS module somehow got zapped by checking fuses, but seems unlikely. I am not sure the next trouble shooting steps to follow.

Vehicle still starts, power steering is offline, lights still flashing. Battery is good.

Are there common electrical faults known? I looked up other threads that seemed similar, but are huge and I couldn't find this specific fault.

 

I take it your method of checking fuses was removing them and re-installing them?
First STOP disconnecting the battery and reconnecting it following the MYTH on the internet. This often leads to other problem by the act of this bad procedure.
Besides if you were checking the fuses by pulling and looking and reinstalling them who know how many times to activate power to and disconnected power to the ECU and BCM????
Well as always, the first thing is to load test your battery. I know you are going to state its fine....
Then you want to check the 4 main batter cable connection. The most important is the ground cable.

Now before you go any further you need to go back and recheck the ECU (no blue tooth programs) a medium grade scanner that connects directly to your OBDII Diagnostic connector and check the 3 main area's of the ECU and then your ABS . If the scanner does not have ABS, then start with what you didn't find when you scanned the ECU the first time.
FYI resetting current or active DTC in your ECU basically turns off the check engine light. Until a problem is resolve it does remain active in the permanent file area of the ECU
Ok now you need to reset your immobilizer. (this may likely be what you disrupted during your fuse checking and battery disconnection procedure?) Go to service steps for your exact Mazda and follow the exact service procedures.

 

I failed to see that you are a new member... Sorry ...
I am at work and it happens a Honda just arrived was flat towed by AAA into the shop that the owner did some of the same things to resolve a no start and xmas tree light up on the dash as you did to your Mazda. LOL
Welcome to the forum

 

Thank you for your feedback! When you aren't making process you start following any web hint/suggestion as the desperation increases! I will go load test the battery, I will verify the 4 main battery cables with my meter (not just visual). My scanner is not a high grade. I am sure my fuse checking led to these issues....

 

You joined a great forum for advice from very experienced members both professionally (1 is a Factory trained Mazda Mechanic and the other an ASE diagnostic tech) in the automotive service field as well DIY that are fundamentally good at trouble shooting even with a somewhat DIY methodology.

Your scanner may not be able to look in the immobilizer(change the battery in the FAB) , BCM or permanent DTC file area, but you can look at your I/M monitors.

 

All I/P monitors are either Ok, INC, or NA, not seeing any faults there.