This is a long sad story with a happy ending
In January 2021, I took my RAV4 EV to Findlay Toyota (Henderson Nevada) for service with the “Check EV System” message displayed. The symptom was that my RAV4 EV would go into "Neutral Mode" when accelerating onto a freeway onramp. At that time, their service recommendation was to replace the 12V Battery which was approved and performed. I paid the core charge to keep the RAV4’s battery which I installed into my 2005 4 Runner and it is still working fine today so that was not the root cause of the problem.
The problem recurred in September (8 days after the Platinum Warranty had expired) when it again shifted into Neutral Mode when accelerating onto a freeway onramp. I was eventually able to get it to get back into Drive Mode again drive it home. I drove it back to Findlay Toyota with the "Check EV System" message displayed (but it was drivable). Their Service Technician verified the same fault and replaced the 12V Battery (again) while spending several weeks troubleshooting it but was unable to pinpoint the root cause of the problem. They even consulted with Toyota Factory Tech Reps AND Tesla Tech Reps without success. At this point, they gave up and recommended that I bring it to a Toyota Service Center in California. My RAV4 EV was now unable to enter Drive Mode under any circumstances so I had to rent an auto transport trailer (at my own expense) to transport it to Crown Toyota (Ontario, CA) in hopes that they could properly determine the root cause of the problem.
The Technicians at Crown Toyota also spent several more weeks troubleshooting and consulting with Toyota & Tesla Tech Reps to determine the root cause of the problem. The technician initially reported that the DC to DC Converter was defective so this was replaced but did not remedy the problem. Their technician then determined that the root cause of the problem to be the Main Drive Battery. We agreed that this cost was prohibitive so I contacted QC Charge to see if they could repair my RAV4.
The Happy Ending: I then had my RAV transported down to QC Charge. Isaac and his team quickly diagnosed the problem to be the Main Contactor which was replaced for $2,500. I am extremely grateful to QC Charge for bringing my RAV4 EV back to life.