I have the same issues that Bum has. My REM will switch to closed loop after about 2-3 minutes of operating. It will then switch back to open and remain in OL.
I have on the display: Eng Temp, O2 v, heater relay v and Open/closed Loop. (mostly open.)
My eng temp is consistently 190* +/-
Relay volts are consistent 12.5 v +/-
O2 v starts out at 4.98. As the engine warms up, the volts drop. Once it reaches operating temp (190*) it runs at 2.0 to 2.3. Occasionally, it will drop below 2.0.
The Renix ecu is supposed to run in open loop until the O2 heater reaches operating temp (~1200*). If the O2 sensors are "operating" as their supposed to, then why does to switch to open loop?
The O2 is relatively new: ~1 yr. I installed NTK/NGK sensor.