HensTeeth

Don't laugh, but check your front number plate. I've posted about this before, I think, but if there's a build-up of dirt behind the plate and/or its supporting plinth, the sensors seem to pick up the damp muck and interpret it as 'something very close'. Hence why it can come and go in damp weather. I did a thorough clean-up and reattached the number plate with new sticky things, and have had no more trouble. ETA - easy to see if it's going to help you - take the number plate and plinth off and see if the sensors suddenly start behaving...

Wheel bearing perhaps? What happens to the sound if you knock the transmission into neutral?

I would imagine that the computer is looking for a valid temperature reading from the sensor. It won't know where the sensor actually is, merely that it's electrically present and that the reading the computer is obtaining from it is within the expected range. So if the sensor isn't connected, the computer logs the fault because it doesn't know how warm the battery is, and so it doesn't know if it's overcharging it or not.

Probably wouldn't be your first choice, but is a conversion to a non-rear steer arrangement feasible, with a rack removal and replacement with tie rods? Mechanically likely to be easier than persuading the computer to let go of its amputated rack, I suspect

The YouTube video (about 2'27" in) in this thread shows the battery voltages in Techstream when you go to register a sensor. Maybe that's where it is? Though I'm not sure 'OVER' as a battery voltage is much help...

Anywhere with birds, they do that... Worse, much worse, I've noticed, when the car is was spotlessly clean. If you're planning to update the maps yourself, the guidance they provide is decent, but make sure you use a decent USB stick. Doesn't have to be fast - I've tried a faster one, and it made no difference to how long it takes, which is best part of 80 minutes. I've done it twice now, and the first time I did it just sat in the drive with the car in Ready mode; the second I went for a drive.

Gulp. You're thinking that stripping the rack down to its constituent components should identify the root cause, with a replacement from Amayama as a backup plan? I'm very interested in how you get on...

That YouTube video, complete with clicking relays, looks like classic symptoms of a low battery voltage. If you have a multimeter, check the voltage at the battery both with the car off and when you're trying to start it. Anything much below 12V and you'll have issues. If you've managed to get it fully charged from an external source (mains charger like a CTEK etc) and you're still having difficulty, and the battery voltage won't stay above 12V for more than a couple of days, you've either got a parasitic drain on the battery, or the battery is kaput. If it's the battery, Tayna now do one which looks an exact replacement for the MK4 GS450h

I've used this crowd a couple of times for map updates which seemed a respectable deal - others are available. Seems new maps for the earliest of the Gen 4 GS have stopped now, but you can get updated to 2022/3, which is good. I've idly wondered about installing a BeatSonic, Grom, or Carlinkit kit to get CarPlay, but not taken the plunge. Lots of chat about those systems on clublexus

That's a fantastic piece of work and very kind of you to have shared it for future use. Mine isn't an F-Sport and therefore doesn't have that particular failure mode, but that's going to save someone a pretty penny at some point in future!

On the assumption that's on your 2013 GS mk4, the reverse light is one side and the fog light is the other, both LEDs as standard. Edited to add - my brother came with me to collect my car when I bought it, and piped up that he'd some bad news for me already - only one of the reverse lights was working. There is only one reverse light... so it wasn't bad news after all! I suspect yours is the same...

Forgive my curiosity - was the spare ECU functionally fine (no damaged components) but not coded to the car in some way? Hence the cloning of the data on the EEPROMs simply matching the spare ECU to the car?

Your original ones look like Denso, which is what used to be the Toyota/Lexus standard fitment. They're available from Euro Car Parts amongst other places. I find them to be efficient and silent on my GS. Can't help on the inserts, but I'd be interested to hear whether they're any good if you manage to source some and decide to take that route.

Could the solution of a Toyota part like on this thread help, perhaps? Edited to add: I know it's a different model, but if it'll physically fit, it looks like there's some adjustment room.

Just a thought - well, two: Could they squeeze in the Hybrid Health check to maintain the warranty on the battery, even if they can't manage the full service? Not sure, but perhaps a Toyota dealer can do a Lexus service for you? Up here in Dublin, the Toyota Dealer in Kilbarrack is still an authorised Lexus service location from when Lexus were sold there.

Try to get it looked at by a competent windscreen repair person as soon as possible - the success or otherwise of a repair is significantly influenced by how soon it's done, so I've been led to believe. Don't know whether you're a member on PistonHeads forum, but there's someone there who goes by the name of Glassman who is very generous with advice, and has a mobile service somewhere near London, I think. Personally, I'd try to avoid a replacement screen if at all possible - especially these days with all the gubbins attached to them, which may need accurate recalibration afterwards.

If the bracket managed to catch the positive terminal, and short to chassis, there's your blown fuse ...

One other quick thought - if it’s been serviced by Lexus Galway, it’s not under warranty is it? Lexus Relax is now in Ireland

Wow that’s some bad luck. Did the garage suggest probable cause for the failure? That’s the first of these engines I’ve heard of suffering any kind of bottom end trouble. Or serious trouble of any kind really- some issues with the top end in the version in the earlier GS but mostly fixed by recalls even then. The only reason I can think of from what you’ve described is that it was somehow very low on oil If it were me, I’d want to understand the reason for the problem before making a final judgement, but given you’ve now had two extremely rare failures in the one car, one which regularly comes close to top of the reliability surveys, maybe there’s more to the vehicle’s past than you’re aware.

From your description, nothing that needs the hybrid system is online, only 12V electrics and not too many of those. I'd check fuses from the 12V battery just to make sure everything which should have 12V has 12V. If that doesn't get you anywhere, the bit that's bothering me is that you said your hybrid battery was unexpectedly very low. That could mean there's something up with the HV system - either inverter or battery, which unless you have skills in that area is going to need specialist attention. Richard at Hybrid Battery Solutions used to frequent this forum - might be worth PM-ing or calling him. Failing that, I think I'd be finding a local hybrid specialist after that. I assume it's now out of any 15 year battery warranty courtesy of the Hybrid Health Check at Lexus/Toyota? Fingers crossed for a nice simple solution

Do you mean Lexus Relax? Terms here. Suspension: Front and Rear Springs; Torsion Bars; Track Rods; Stub Axle; Cross Members; Sub Frames; Wheel Bearings (limited up to 160,000km); Hubs; Shims; Lock Nuts. So unless you're over 100k miles, and it's the Relax warranty, I'd wave a copy of their own document under their noses and see what they have to say. Relax is still new enough, so it's possible some dealers might not be as au fait with it as they ought to be.

As others have said, it's going to depend very much on the kind of journeys you do. Short are always going to be lousy from an MPG perspective. I have a 4th gen GS450h, and my long term average is nearly 44mpg according to the computer, which I find a bit optimistic. However, a lot of that mileage is on relatively clear motorways, which balances the small amount of round-town trips I make. It is slowly becoming a no-car zone round here, so difficult are the authorities making it to move about by car, so most of the local trips are only to supermarkets, to bring children to school or activities. However, a fully loaded car with family on board, and a boot so full I was concerned it wouldn't shut yielded nearly 50mpg on a 700 mile round trip on motorways and A roads, with a bit of tootling at the holiday destination. So I'd be very disappointed with a 300h to be getting what you are If I drove it under the same circumstances as the 450h. Driving style plays a part though - I'll try to read the road ahead and never accelerate towards a red light or stationary traffic as a lot of people seem to do. I mostly (ahem) keep to the speed limits too. If your journeys require having to make rapid bursts of acceleration followed by braking to nip into gaps (I'm thinking central London or other large towns), it's not going to help, and would go a long way towards explaining the values you're getting. Honest John's real mpg site https://www.honestjohn.co.uk/realmpg/lexus/gs-2012/300h, shows quite a range of what people actually get.

Well done for changing the bearing successfully. I have a Mk4 and am wondering when the inevitable will be required - don't seem to hear so many stories about those, but perhaps that's simply age and numbers related. For what it's worth, mine makes a noticeable noise when it's been run at speed for a while, such as a motorway, and you pull up at a toll booth or whatever, but is essentially noiseless when starting from cold in EV mode. Not sure if you've seen or used the official refill procedure, but I believe the level using the level plug needs to be checked with the engine running and at 35 (ish) degrees, so that the oil is in circulation at that point. Is this any help: https://slideplayer.com/slide/14432904/ Page 27 onwards.

Not sure whether you're talking about the IS300 in your profile or the GS450h in the title, but some discs have different part numbers for left/right sides of the car - on the GS450h F-Sport and Premier models: see https://lexuspartsdirect.co.uk/product/lexus-gs450h-phase-4-front-brake-set/ for example. The mechanism by which the discs rotating 'backwards' would cause squeal is not clear to me, but I've a vague recollection that the cooling fins between the two braking surfaces are 'handed' to scoop maximum airflow for cooling, so it's probably worth getting it right for that reason alone, if they are.

There are 4 parking sensors on the front. If you put earplugs in and ignore the racket and the big red bar (which is shared between the inner two sensors), do you get markers on the screen showing up from the two front corner sensors if objects or people get close to either front corner? Perhaps put something close to the other two sensors, a wheelie bin works well, and see if they're working properly. If the outer two work as expected, the control unit's probably OK and assuming the wiring is fine, it could be either or both inner sensors dirty or defective. Step one - check for dirty and or obviously damaged (stone chipped etc.) sensors - free and almost no effort. Step two - check the front number plate and the support plinth. Muck can build up behind the number plate and mounting, especially if the number plate is screwed rather than stuck on for some reason, and the sensors seem to be able to 'see' this wet muck and interpret it as a close object. Try taking the front number plate and its plinth off and see whether the sensors miraculously behave. If they do, clean everything up and I'd recommend using the double-sided foam stickers to hold the number plate to the plinth rather than screws. If neither of these things get you anywhere, you're probably into taking the front bumper off and swapping one or both sensors. If you have access to Techstream or a good code/live data reader, it might tell you which one is giving false readings.