Vincenze

After diying so much on my beloved RX400H- new rad, o2 sensors, height adjuster, brakes. It was running so well. Just needed to upgrade the ancillary battery.

Then I zap the fuses like a moron by reverse polarity. It was the end of a tiring day and I had rotated battery and just messed up. 5 seconds of big sparks, headlights full on. Idiot.




Replaced 5 minor fuses. Main fuse blown, which is a good thing.

Getting dead p/s, abs, locked shifter, brake light, blank Nav screen etc. The car doesn’t run very well or for long.

The main fuse is a pita to replace. I realise now why some of the PAL main fuses you can buy have open ended spears rather than holes you have to screw into.

I was wondering if I could tear out the copper spades of the busted fuse so each spear would rip off each bolt. Then I could push in one of those open ended spear types.

I guess a temporary fix rewiring the ends of the busted fuse is mad.

So depressing. Lexus dealer is quoting £375. It is a crap job. And of course there may be more problems with the DC inverter (replacement cost could spell scrapping the car) or the P/S fuse inside the HV battery.

Margate330

Hi friend, don't let it get you down- we have all screwed up bad and been there many times. lol
Hoping everything is gonna be ok and just some sparks and fuses.

Ok so hard to figure out exactly where you are now- so are you saying you already replaced that big blown main fuse in the pics?
I hear it bolts in from the back side with screws but have no way to confirm so if you get it out plz share pics of your fix for us.

Also, the "short pin fuse" is famous for blowing at reverse polarity and is not protected by main fuse- it's the one in the fuse box next to brake reservoir that is not marked(see below).
Below are other fuses that branch in a different direction and not protected by main fuse that may need checked.
PS- I don't recommend using anything that isn't spec or modifications for that main fuse for fear of a potential harness fire in the future.
Hopefully others have ideas...


Location of "unmarked" short pin fuse- hopefully get some of your stuff back...






Also, with the short pin, can check these too.

Vincenze

Cheers for the encouragement Margate. I haven’t replaced the main fuse yet. It’s a blooming bit of brain surgery to do.

I looked at the short fuse. It’s not blown. Didn’t understand what it was at first.

i suspect the car will be ok when the main fuse is replaced. I did wonder if I could pull out the main fuse and rip it off the the two bolts one on each spade. I thought I’d use long nose pliers and just haul both sides up and let them cut from the bolts.

I fear only that the inverter or P/S fuse on the HV battery are ruined. I did wonder if the inverter can handle bigger amperages as it steps down voltage. Anyhow I want my Rx400h back. I love driving it. 115k on the clock.

Margate330

Would love to see walk thru with pics for that main fuse replacement if you can.

Looking at the drawings I suspect the "Short Pin" fuse is a special "fast blow" style fuse judging by the components downstream from it are very sensitive components- Nav, radio, Body ECU, etc- but I have no way to confirm this so only a guess. but it knocks out a lot of stuff.

PS- if there is an easy mod for main fuse replacement that meets specs like to see that too.
PS- power electric steering is stitched in with other things- for starters can try MPX-B1 fuse & ECU IG No. 1 fuse, if no problem found there will need to dig in deeper but the without the Main fuse there is no power(thru ignition switch and relay) to the ECU IG No. 1 fuse- thus no power steering...

Yeah until that main fuse is replaced you won't know where to go next.

Vincenze

Will let you know route I take. I have ordered the 120 amp fuse. Arrived this am. Copper structure. I’d like to test it before it goes in as the plastic housing clearly isn’t the same quality as original. But it’s not the plastic that breaks the circuit.

Vincenze

OK, so, I rammed in the 120 amp copper spades like a crown over the blown main fuse metalwork. It was a very tight fit and led me to believe that contact was good. The bit I used to ram was from a new 120 amp fuse that had arrived by post. I made sure the blown part did not join (because the pressure of ramming brought the original blown fuse ends together). I assumed that you shouldn't have two 120 amp break point paths. It was pissing down with rain so haven't photographed.

1) I installed a new, tested full charge, 12V battery.
No "READY" was given when I turned the key. P/S / ABS and Brake warnings appeared as before MAIN FUSE makeshift fix. Steering wheel wouldn't tilt / no NAV display / windows dead / Shifter locked in park
BUT engine fired up as normal and ran smoothly. There were clicks and thrums coming from the front.

2) I did the "Accessory" turn with the key, pumped the brakes twice and turned engine on. THEN I got the "READY" signal & steering wheel shift. Warning lights went off/ Nav display came to life (HV battery showed 3/4s charged..looked normal). For a second I thought problem solved. It ran for 5 seconds then flipped back to 1) status. But, the Hybrid warning did come on.

I had hoped that I would prove that an operational Main Fuse (admittedly, a makeshift job with risks) could solve this. That's where I am at the moment. I checked a couple of the mini blades I had replaced (that blew after the battery short). The fuses were fine.

I don't know what this means. Is it possible the MAIN FUSE makeshift fix is fouled up? I checked it and the crown is tight on the old metalwork. Sure it isn't satisfactory beyond testing

I guess I need to see some codes on techstream

Margate330

Sounds like you were almost there.
Not sure but if it was my car I would put the main fuse in tight and go from there- and looseness or heat felt at that fuse could mean poor connection and a voltage drop. Any voltage drop across the fuse will increase current inversely proportional.
Visual inspection of other fuses could save time too since a cracked fuse could test good with a meter but have voltage drop or near open with a load demand on it.
Fingers crossed for you...

Vincenze

Cheers Margate. Yes, my feeling too. Nearly rejoiced.

I think my main fuse makeshift fix detached or fluctuated voltage in some way. I might even solder the 120 amp section onto the open bridge of the blown fuse.

I’ll go through the mini fuses again.

I actually think (hope) the 400 is a more robust vehicle than supposed. Mind you, it’s electrics and warning lights certainly do get called into question a lot in the forums.

What exactly moving the key to ‘accessory‘ and back then pumping the brakes twice before full
ignition does exactly...felt more like jiggerypokery. I can’t remember where I read that this manoeuvre could revive the system. It’s not the ICS reset. Anyhow straight after the dance my ‘Ready’ came on and things looked very hopeful albeit brief.

I spoke to an auto electrician who gave me the confidence to temporarily bridge the fuse. I asked him to quote for the Fuse swap. When I mentioned it was an RX400H I thought I discerned a faint groan.

Plus1RX

Is this any help?

Vincenze

That sort of thing. Though that’s a lot more accessible.

Vincenze

RX400H Junction box with wedged in fuse/relay insert.
Get that out and Main Fuse bolts can be accessed

mmarshall

Deleted by MM

Vincenze

Interestingly the short pin is not a fuse per se but a device (the dealer pulls) to reduce electrical drain in motors left on the forecourt.

Vincenze

Naughty temporary fix

So, my 113K miles RX appears to be working fine thank god. My temporary insulated crocodile clip fix holding in a 120 amp rated wire plus a non conductive block between the split fuse seems to work.

All electrics work except the steering wheel tilt at ignition. Will have to check that.

No warnings yippee

Brand new auxiliary battery behaving itself and maintaining 14.2 V charge.



Consistent charging


A big thank you to Margate for the encouragement and very handy diagrams.

Margate330

Good to know our cars can take a hit like that without blowing out all the electronics as you just proved.