As stated in prior posts by me the heated grips controller WAS proven the fault and was replaced. It failed on the bike as well as on the test bench when hit with freeze spray. The new controller was also hit with freeze spray on the test bench before it was installed and continued working fine. The grip heat temp sensors are located near the grips just where the wires enter the handlebars. It does seem that when you ride in really excessively cold temps like I do it is possible this cold air can blow into that hole in the bars and cool the grip heat temp sensors to give a false error indication to the controller. But as I posted just above the grip heat worked great at 15F without my handlebar muffs. My normal is that when I ride in any temp below 40 (getting older makes one less able to handle cooler temps) I do use the handlebar muffs. I don't usually turn on the grip heat at that temp but maybe at below 35F I will. The handlebar muffs shield the handlebars so cold air doesn't blow into the holes where the grip temp sensor is located so no false error can happen. The design is not the best.
If you are getting a flashing red light at the left grip indicator then you need to pay attention to the code that flashing shows. Here is the section from the service manual on the fault indication, the same information is in the owner manual. The bold part in step 5 is the error code to look for to determine where the fault is. The fault code shows before you turn off the bike when the heated grips fail and after the self check is done if a fault is found.
Handlebar Heater State Indicator:
1. After turning ON KEYLESS Main Switch, a self-check is performed with the
LED indicator flashing in a 1-white and 1-red format.
2. After KEYLESS Main Switch ON and indicator self-check, in the event of a
Handlebar Heater anomaly, the indicator will flash in red, with the Handlebar
Heater function disabled. (Refer to anomaly states below for indicator flashing
modes.)
3. After KEYLESS Main Switch ON, press and hold the button to activate
Handlebar Heater. Indicator lights in white constantly for normal operation.
4. Turn KEYLESS Main Switch OFF or press and hold the button to deactivate
Handlebar Heater. The indicator will go out, indicating the function is switched off.
5. If Handlebar Heater is faulty, the indicator will flash in red.
When Handlebar Heater function is OFF, anomaly states are as follows:
a. 1 flashes (on/off) per 0.2s followed by 2s off: Handlebar Heater function is
faulty.
b. 2 flashes (on/off) per 0.2s followed by 2s off: Handlebar Heater temperature
sensor is faulty.
c. 1 flash (on/off) per 0.3s followed by 0.3s off: Handlebar/ Controller Circuit is
faulty.
After eliminating the fault and re-starting (Key Off -> Key On) the vehicle,
indicator will resume normal operation.
Clicking the button when the indicator is flashing in red will stop the flashing. For
the sake of your safety, please go to a KYMCO dealer for check-up.
I have found that I haven't needed to turn up the heat any more than the lowest setting. I have tried medium and even high for short times but those were too hot for me even below 10F with the muffs also in use. In Dec 2022 I rode in temps at around 6F with the muffs and grip heat on low and was toasty warm. It is all working fine for me since the controller was replaced last year.
BTW- riding at any temp above freezing should never cause the grip heat temp sensors to fail.