I recently visited hilly areas I'm my lexus rx 450 h 2010 model. Upon reaching at 1700 meters, the check light for hybrid system came on. Upon further climbing, traction slowed and finally there was no traction. Removed the 12v battery negative cable and the system was reset and all was normal. I continued in the hills and faced this problem twice again. But these were only caution light which extinguished after removing the 12v battery cable, which would reset the system. Since returning to lower altitude, the vehicle behaves normally. I drove 1600 kms in 2 days and got an average of 11.5 km/litre. Please guide if the car behavior at higher altitude is expected because of rarer atmosphere.

 

That's only 5552 feet about the altitude of Denver.
Get your 12v battery checked. How old is it? If original replace it. When they start to fail the lower voltage creates many different problems. The altitude may have been the stress test it just failed.
There are other sensors on the engine that adjust the gas engine fuel-air mixture for altitude and you could get the vehicle checked for stored codes.

 

I am afraid going uphill on a mountain is a typical condition that reveals weak HV traction batteries. Do you have other bad battery symptoms like leaving the HV battery in full bars overnight and then the first couple of minutes to lose 2-3 bars? You might have to change or rebuild your HV traction battery soon. I hope not!

 

Take a guess on how much the traction battery/motor is active when you are moving at 45mph +?

Salim

 

Many thanks. I will follow your advice. Welcome any further guidance from members on the subject please.