‘22 Lariat - SHIFT SYS FAULT - random and inconsistent

[Cliffordom24]

hello, I purchased a used 22 Lariat hybrid last June and up until now it has been great. I’ve spent a long time reading through the forums trying to find out what others did when they had the “SHIFT SYS FAULT” error display. My story with it has been anything but fun.

3/22/26 - car throws fault for first in downpour on exit ramp, applies e-brake when coming to stop. After trouble restarting, drives with CEL and Wrench on. Exited to parking lot, waiting for couple hours, would engage D and R but wouldn’t move. Come back next day and it drives home with CEL on. Disconnect G terminal on battery and CEL goes away. Drives fine for next few days.

3/26/26 - install new H5 AGM battery after reading forums about battery issues. Previous battery was Ford Motorcraft replaced in 2/24 according to sticker. Reset BMS, car drove fine still.

3/27/26 - 4 hour trip, no problems until last 20 minutes when fault throws up again, pull over, ebrake turns itself on, restart car, and no warning lights, finishes trip fine.

3/31/26 - after a couple 20 minute runs without issue, I leave to head home and get 3 hours in without issue when the field reappears, similarly do a restart like before and keep going, this time however it came back within a few minutes/miles. It repeatedly came back after a couple minutes and miles of driving along with a “transmission can’t engage park, use parking break to stop” or something similar fault. After a couple times dealing with the Mav constantly and randomly throwing faults and stopping itself, I made it to an exit and parked in a gas station. It currently has just the CEL on (normally it went away during the period of multiple faults).

I truly have no idea what the fault could be and I am waiting for a tow and to get an appointment at a dealer. I was wondering if anyone has had this fault get progressively worse, and have it be not fixed by a new battery, I want to tell the dealer where to look first to save time and money.

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[bgn]

Recommend you pull the codes it's throwing. Some folks have had issues with the gear selector.

https://www.mavericktruckclub.com/f...ft-sys-fault-error-no-start.39113/post-702358

 

[HeyBales]

Since you are driving - the 12V system is no longer powered by the 12V battery - but the DCDC converter.

So don't see how it would be a battery issue, with a term like Shift system issue.

Sounds like it is losing track of what position the shifter is in, or knows it can't read a sensor to know that info.

Wires.
Look for evidence of rodent chews.

 

[Tech Tye]

Had these issues when I first got my 23. They put 2 transmissions, inverter with no luck. I already upgraded the battery to an optima yellow top. The last hail marry was to replace the entire wire harness on the front of the car due to a 40 pin connector under the front left bumper had pins corroded in it. Warranty wouldn’t let them just fix that , so it required a total new harness replacement. 6 months later I finally got one . All good now. So have your service team check the 40 pin plug for corrosion . If it’s out of warranty they could just cut the bad pins out and solder the wires together. I brought the tech a big tube of silicone grease to put in the new 40 pin so it doesn’t happen again as it never had any.

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