How did you make out? I had same problem and replaced the temp sensor with no results so kept digging and found a loose pin in harness plug to the sensor. I borrowed a handset to find this fyi.

OVERHEAT fault can be caused by Access 3 heatsink over temp or drive motor over temp. Drive motor has internal temp sensor. You really need a handset to see what temps are being reported. Check wiring to drive motor especially under the handle cap where the handle pivots and the brake switches are, there was a recent tech bulletin about these wires being routed incorrectly and causing problems, that's most likely where your problem will be.