Hi Marok,
I borrowed a ramp for a day and drained the ATF out of the gearbox and removed the Hybrid pump (four bolts) and wiring loom to the pump controller. I removed the pump impeller housing screws (3 screws) and found that the shaft was seized and wouldn't budge. So I took the motor housing off (another 3 screws) and found that the front bearing was seized, preventing the motor shaft from turning.
It is a very clever and simple well engineered design, the pump and motor are in excellent condition, it was just the bearing that had failed. I took the bearing to a bearing supplier and they had one in stock for £7. They said this is a common size bearing readily available. I also bought the rear shaft bearing at the same time and re-assembled it, filled the gearbox up with new ATF, cleared the P2797 code and the car has now run perfect for the last 3 months, without problems.
Someone else on this forum read my post and did the same on his LS600h and he now has a working pump again too. He also has two friends with the same problem and I believe they have repaired theirs too.
A relatively simple and cheap repair, saving thousands of pounds. Lexus quote 9 hours to replace the pump. I took 7 hours, including investigating the problem and driving to the bearing shop. Just shows, they even charge you too many hours for a job that should take them no more than 4 or 5 hours to do when replacing a new pump.
This is the fault that every GS450h and LS600h owner dreads. EVERYONE SPREAD THE WORD THAT THIS IS AN EASY FIX AND DON'T GO TO A LEXUS DEALER WITH THIS PROBLEM AS YOU WILL BE RIPPED OFF !!! Otherwise, you will be throwing away a perfectly good pump for the sake of a cheap bearing.
I bought £50 worth of genuine ATF, 2x bearings at £14 and a ramp charge of £100. If a garage was to do this for you, it should cost around £500 parts and labour.
Giles.