Lexus RX400h message 'Check Hybrid System' and it won't start

Your Lexus's "check hybrid system" warning light means that something is malfunctioning in your vehicle's hybrid system. It could be a problem with the hybrid battery, but it could also be a blown fuse, a faulty fuel pump, or an inverter failure, among other issues. Cold weather can sometimes trip the system, too. your starting battery may be bad

VSC could also be battery problems

2006 Lexus RX400H hybrid .
and long story.(you added and very very good)
and if was mine, my story would be same, park it and wonder what to next.?
this car is very complex, unlike ICE real cars were simple and still are to a good extent.
I do wish you find a good shop to cure all that.
a full service manual in hand may do the trick.IDK.

good luck! and be SAFE.

use the scan tool as the hybrid starts and fails to light off the engine, see DTC code for that.
scan before ,during and after failures
and use the pending button too on t he scan tool as here may be marginal or intermittent failures

also (Im no hybrid guru) but some hybrids do not run the engine (to save fuel) until the battery has some amount of discharge detected.
some even have switches to set the mode you want,save fuel or save battery life, IDK this car.

Summary: Toyota is recalling certain model year 2004 avalon vehicles; 2004 and 2005Camry, Camry Solara, highlander, and sienna vehicles, 2006 highlander hybrid; 2004and 2005 Lexus ES330 and RX330; and 2006 Lexus rx400H vehicles manufactured from June 1, 2004 through March 31, 2005, equipped with the 1mz-fe or 3mz-fe ...7 days ago

2004 Toyota Camry Recalls ' CarComplaints.com

https://www.carcomplaints.com/Toyota/Camry/2004/recalls/..
Recall on camry 2004 Le Google Search

Sorry no idea ,ask me about a ford cortina from the 60s or a older car with no fancies but a hybrid is something i havent worked on as yet ...an electric milk float from 40 yrs ago yes i can repair them

my lexus 450 hybrid system said check and the engine won't start
what shuold i do

Can you ensure the car is in park?
Move lever to D and then back into Park and see what happens.
I have heard with this particular model, we have the environmentally unfriendly RX 330, that the batteries lack of charge may play havock with the electrics in these cars.
I religously charge my battery every six months with a smart charger so its always in peak, I also find a quick zap at the first cold snap of autumn / winter gives us trouble free motoring.

Hi, you have done something that is not recommended. Avoid disconnecting the battery because it erases the system info that operates like our brain of the car. There may be shortcuts but I recon you going to a dealer and reloading the system info. If your battery is low it is a very good move to replace with a new one before it is too late. It is a common problem with Lexus RX H.

Does it still have a warranty on it? If so I would use that while you got it, and get it fixed free of charge. There is probably a cosmetic plastic cover hiding the alternator. However if you locate the belts than it will lead directly to the alternator.

if this car has the daytime running lamp option they are supposed to be on.

bad oil pressure sending unit, dealer needs to chk it and replace it.