MK4 LS400 ECU swop and capacitor issue

Razor61 · April 20, 2023

As a lot of people are already aware there is/can be an issue with the ECU on the LS400 with leaking capacitors causing strange issues. In the worse case damaged circuit boards which can render the ECU duff/bad/unusable.
This seems to affect the earlier mk1/2/3 but can affect the Mk4 LS400 apparently although not as much, but I suspect this is just down to the age of the car/ECU or maybe the capacitor issue was rectified on the MK4.
For the earlier mk1/2/3 another 'good' or refurbished ECU with new capacitors can simply be installed and all is good, I know this is definitely the case with the Mk3 from personal experience.
For the MK4 ECU it's a different story, if you don't have an original master key for that particular ECU.
The MK4 ECU has the EEPROM Chip or EEPROM IC (IC900 I believe) for the immobiliser on the ECU itself and this stores the 'key' information. An EEPROM is a 'electrically erasable programmable read-only memory'.
This means that after swopping the ECU the car won't start because the replacement ECU knows nothing about your original keys which are programmed to your original ECU and therefore the car is immobilised.
Because of the capacitor issue I bought another ECU for my 1998 LS400 just after I purchased the car 17 months ago with the idea of replacing all the capacitors so it's good for the future but I didn't realise about the immobiliser thing at the time.
After some research I found 2 x possible methods/solutions for this.

Method 1 - if you are good with a soldering iron or know someone who is, you can swop the 8 pin immobiliser EEPROM chip/IC (IC900) from your original ECU, install into the replacement ECU and all should be good.

Method 2 - reprogram the EEPROM chip/IC (IC900) on the replacement ECU and 'zero' all the data for any key codes stored and the virginize key entries (leave the valet key lockout code) effectively all zero except the valet key lockout entries - this 'virginizes' the immobiliser/ECU and puts the immobiliser/ECU into programming mode ready to accept new keys. This method is involved and you need to remove the chip (ideally), connect to an EEPROM programmer, download and save the current data to a file using software, edit the data, write/upload the new data to the EEPROM, resolder the EEPROM chip to the circuit board and it should work ok. Once you refit the ECU there is a procedure for programming the keys one by one until 3 new keys are programmed. First 2 are master keys and third key programmed is designated as the valet key.
Or upload the data from the working ECU EEPROM and write it to the replacement ECU EEPROM, probably the better option.

Has anyone on here attempted either of these methods or have any advice, particularly method 2, and maybe have information on what EEPROM programmer to purchase to do the job?
I believe the EEPROM programmer needs to be able to program 93xx/95xx series 5v EEPROM used in the automotive industry.
I've no doubt I can do method 1 and swop the EEPROM but I'd prefer to reprogram the EEPROM on the spare ECU I have if possible, I don't want to end up with 2 x ECU's which won't work.

Malc1 · April 20, 2023

32 minutes ago, Razor61 said:

can render the ECU duff/bad/unusable.
This seems to affect the earlier mk1/2/3

......... well on my Mk3 I've been thru' all this ECU mullarkey with cutting out etc, revs dropping out to net zero ..... BUT for some inexplicable reason, and I'm eternally grateful to 'im up there ... all this crap has ceased and she's running a dream now ..... . fingers always xd tho' on this and all other Mk3 issues 😉

Malc

Tinonline · April 20, 2023

31 minutes ago, Razor61 said:

As a lot of people are already aware there is/can be an issue with the ECU on the LS400 with leaking capacitors causing strange issues. In the worse case damaged circuit boards which can render the ECU duff/bad/unusable.
This seems to affect the earlier mk1/2/3 but can affect the Mk4 LS400 apparently although not as much, but I suspect this is just down to the age of the car/ECU or maybe the capacitor issue was rectified on the MK4.
For the earlier mk1/2/3 another 'good' or refurbished ECU with new capacitors can simply be installed and all is good, I know this is definitely the case with the Mk3 from personal experience.
For the MK4 ECU it's a different story, if you don't have an original master key for that particular ECU.
The MK4 ECU has the EEPROM Chip or EEPROM IC (IC900 I believe) for the immobiliser on the ECU itself and this stores the 'key' information. An EEPROM is a 'electrically erasable programmable read-only memory'.
This means that after swopping the ECU the car won't start because the replacement ECU knows nothing about your original keys which are programmed to your original ECU and therefore the car is immobilised.
Because of the capacitor issue I bought another ECU for my 1998 LS400 just after I purchased the car 17 months ago with the idea of replacing all the capacitors so it's good for the future but I didn't realise about the immobiliser thing at the time.
After some research I found 2 x possible methods/solutions for this.

Method 1 - if you are good with a soldering iron or know someone who is, you can swop the 8 pin immobiliser EEPROM chip/IC (IC900) from your original ECU, install into the replacement ECU and all should be good.

Method 2 - reprogram the EEPROM chip/IC (IC900) on the replacement ECU and 'zero' all the data for any key codes stored (except the valet key code apparently) - this 'virginizes' the immobiliser/ECU and puts the immobiliser/ECU into programming mode ready to accept new keys. This method is involved and you need to remove the chip (ideally), connect to an EEPROM programmer, download and save the current data to a file using software, edit the data, write/upload the new data to the EEPROM, resolder the EEPROM chip to the circuit board and it should work ok. Once you refit the ECU there is a procedure for programming the keys one by one until 3 new keys are programmed.
Or upload the data from the working ECU EEPROM and write it to the replacement ECU EEPROM, probably the better option.

Has anyone on here attempted either of these methods or have any advice, particularly method 2, and maybe have information on what EEPROM programmer to purchase to do the job?
I believe the EEPROM programmer needs to be able to program 93xx/95xx series 5v EEPROM used in the automotive industry.
I've no doubt I can do method 1 and swop the EEPROM but I'd prefer to reprogram the EEPROM on the spare ECU I have if possible, I don't want to end up with 2 x ECU's which won't work.

I’m surprised you can’t reprogramme the unit in situ…inspite of security measures: or that Lexus can’t.

Is the solution to have to hand over the unit to a specialist to take care of the process/ or replace capacitors only so as to avoid the issue? Or do as you intend given your knowledge and capability.

Razor61 · April 20, 2023

47 minutes ago, Tinonline said:

I’m surprised you can’t reprogramme the unit in situ…inspite of security measures: or that Lexus can’t.

Is the solution to have to hand over the unit to a specialist to take care of the process/ or replace capacitors only so as to avoid the issue? Or do as you intend given your knowledge and capability.

Thought about Lexus and they could probably do it, if I dismantle the glove boxes to get access and take the car in with the replacement ECU the cost may not be too great. I’ll find out.
Specialist is another option of course but I’d rather do it myself if possible and then I could repeat the process for someone else if needed.
Been in touch with Relentless Motorsports in Texas and they can either remove the immobiliser (another option) or reset the ECU, at the same do the caps as well. Just waiting for a price. There will be someone in the UK that could probably do the same as well.

Howplum · April 21, 2023

From memory the total mileage is also recorded on an EEPROM, as I discovered when I changed my instrument cluster. I was fortunate in having a friend who repairs computers so he swapped the component for me. Anyway, if you're changing the cluster it might be worth bearing this in mind.

Razor61 · April 21, 2023

2 hours ago, Howplum said:

From memory the total mileage is also recorded on an EEPROM, as I discovered when I changed my instrument cluster. I was fortunate in having a friend who repairs computers so he swapped the component for me. Anyway, if you're changing the cluster it might be worth bearing this in mind.

Correct, there is an EEPROM on the cluster for the mileage. I swopped out my cluster cos of a faulty temp gauge but retained the main board so mileage was correct.
I've decided to have a go at reprogramming the immo EEPROM on the spare ECU and have a go at the mileage EEPROM on a spare cluster I have, mileage can be edited but takes a bit of working out which bits of data need amending. Its is possible though.
There is a nice piece of kit from Autel for this, XP400 Pro, but it's £500 or £1600 for the XP400 Pro and the fancy key programming tablet/tool to make things easier. Way to much money for what I want.
Found a decent EEPROM programmer that will do the job I think, there are lots on eBay but they need 'altering' for the EEPROM type used in automotive - didn't fancy that and I wanted a complete device rather than bits of circuit board, adapters and wires. I can either use the connecting 'clip' to attach to the chip on the board or remove it and plug it nicely into the socket on the EEPROM programmer. I'll give it all a try when it arrives and report back if I'm successful or not.

This is the one I bought plus the clip and a couple of other 'plug in' chip sockets.

Razor61 · April 25, 2023

EEPROM programmer delivered today, looks a nice piece of kit, and some standard 8 pin IC sockets for the dash mileage EEPROM. Just waiting for other bits, blank 93C56 EEPROM's for the IMMO to practice with, workstation magnifying glass so I can see the small IMMO EEPROM if I need to remove it, solder paste, good quality solder wick, flux pen and some flux remover/cleaner (leaving flux residue can cause corrosion)
I also ordered a lot of caps from DigiKey (bought in lots of 10 in most cases), enough to do a few Mk4 and MK1 ECU's (I have a Mk1 ECU from when I was thinking of buying a Mk1 a while ago) and a few Mk2 and Mk3 probably. Sounds extravagant but for the cost of them versus shipping cost, it was worth buying a lot.
After I have a play with the programmer and blank 93C56 EEPROM's...........the plan is:
Have a go at reading the IMMO EEPROM on the board - if that is successful I'll save a dump file of the data - reprogram the EEPROM to reset/virginize it - read and save this new reset/virginized dump file - replace all the caps - fit ECU to the car - connect Battery - add my existing keys in programming mode (if it works) and see what happens.
If I can't connect to the IMMO EEPROM on the board, I'll remove it, stick it in the programmer and carry on as above.
If it all goes well, the car starts and runs for a while with no issues etc, I'll swop the original ECU into the car and make sure everything works as it did before and the keys still work.
If that is also ok, I'll put the replacement ECU back in and replace the caps on the original ECU. Then swop them around again so the original is back in the car with new caps and the VIN is correct.
That's the plan but may be subject to change and include a lot of frustration along the way😃

Malc1 · April 25, 2023

blimey, if we was in Holland i would say it's all absolutely Double Dutch to me 🤣

Malc

Razor61 · April 25, 2023

23 minutes ago, Malc1 said:

blimey, if we was in Holland i would say it's all absolutely Double Dutch to me 🤣

Malc

Have a look at this, and it’s in English not single or double Dutch🤣 I bought a fully assembled programming device rather than a diy one, nothing wrong with that by the way and I could build one no problem.

https://www.toyotanation.com/threads/diy-immobilizer-hacking-for-lost-keys-or-swapped-ecu.1306497/#post-10860457

Basically, all that stuff is to reset the immobiliser/chip to ‘factory’ settings, for want of a better expression, with no ‘keys’ stored ready for new keys to be programmed to the car/immobiliser. Simple thing in theory but not in reality, simple with £1000’s of fancy equipment but the same can be said of a lot of things.
Thinking about it all again, if I can retrieve and save the immobiliser ‘key’ data from the existing ECU without removing the tiny ‘chip’, then I could simply ‘clone’ or ‘write’ the ‘key’ data from my existing ECU to the new ECU. I’ll experiment on the replacement ECU and retrieve the ‘key’ data then take it from there.

Razor61 · May 9, 2023

Update on this and it’s not good news. Cloning the immobiliser key data from one ECU to the other hasn’t happened yet, more involved than I first thought but I will keep at it.
I then thought I’ll replace all the caps, not as simple as I thought. I struggled to remove the caps in the first place, done this in the past although it was over 30 years ago. I tried all sorts, iron temp, solder, flux, solder sucker and every trick I could think of but still struggled. I replaced 4 caps eventually and removed 1 but then decided to stop. I was either doing something really really wrong or I’m just too old now or don’t have the skill anymore or all three🙄
I since found out that the 97-2000 VVTi ECU is more difficult to work on than the earlier ones, more difficult removing components apparently and is more sensitive to being worked on. Maybe that’s why I struggled.
On the up side I found a company willing to replace the caps, ATC Drivetrain in Cannock. I saw this company on Car SOS the other day, 90’s MR2 with an ECU issue and needed a new IC and capacitors. ATC tested it, diagnosed and repaired. They can’t do the same with an LS400 ECU but are willing to replace the caps if supplied.

Malc1 · May 9, 2023

Reading way back on here somewhere that there is a company near Rochester Kent does this stuff .......... or maybe I'm imagining that !

Malc

Razor61 · May 10, 2023

I've had a rethink about all this after my epic failure😉
The original plan to rebuild the spare ECU (cap replacement) and reset the immobiliser has been scrapped, instead I'll be sending the original ECU out of the car to 'Japanese ECU ECM PCM Repair' aka 'Lscowboyls' in the USA. Yes the car be be off the road for a while and it won't be cheap but once all the work is done on the ECU and refitted to the car there won't be any chance of the ECU Capacitor issues and there's no need to mess with the immobiliser. I decided this after talking to Bill (Lscowboyls) about the whole thing and what's involved replacing the capacitors.
I should have done this in the first place but you live and learn....................
It's more complicated on the 97-2000 VVTi LS400 ECU (apart from the immobiliser thing) for a few reasons, if anyone want's to know the ins and outs of it all then pm me and I'll do my best to explain. If you're thinking of attempting this yourself on any of the LS400 ECU's, my advice is................don't do it and have it done by an expert who knows what's involved, not just electronics soldering but an experienced expert in rebuilding ECU's with this issue, i.e. 'Lscowboyls' as mentioned above.
I will continue working on the immobiliser thing on the spare ECU to see if I can reset it or disable it and also continue working on the mileage adjustment on the instrument cluster.

Razor61 · May 10, 2023

So the immobiliser chip ‘project’, tried reading the immo chip ‘in circuit’ or ‘on the pcb’ and no joy, even with shorting out the oscillators.
Took the plunge and removed the immo chip from the pcb, easier than I expected. Inserted the immo chip into the EEPROM reader and hey presto I could read the data, promptly saved the data to a file on the computer and I’ll examine it tomorrow and edit it to ‘virginize’ it so it will accept 3 new keys.
Before hand I practised removing the same type of chip on a scrap computer pcb to give me some confidence that I’ve not totally lost my previous soldering skills😀
By trial and error using a hot air soldering rework station I’ve realised I’ve not totally lost it.

Scribe · May 11, 2023

Paul, I hope I never have to go through all this, but if I did, how would I know I had a faulty ECU or capacitor issue?

Malc mentioned revs dropping and the engine cutting out, and this happens to me after the battery's been reconnected/charged from completely flat, but after a minute or two it sorts itself out and idles normally. Is this the ECU resetting itself?

Malc1 · May 11, 2023

Andrew, this that I mentioned is usually specific to the Mk3 alone whilst being generally run around and used ........... however, in the USofA there seems to have been a recall by Lexus to change the ECU but sadly not here in the UK ...... BUT of course that must have been a quarter century ago or more

I'll just avoid the need to buy a Mk4 tho' . ............. all seems so terribly complex 😉

Malc

Razor61 · May 11, 2023

2 hours ago, Scribe said:

Paul, I hope I never have to go through all this, but if I did, how would I know I had a faulty ECU or capacitor issue?

Malc mentioned revs dropping and the engine cutting out, and this happens to me after the battery's been reconnected/charged from completely flat, but after a minute or two it sorts itself out and idles normally. Is this the ECU resetting itself?

The capacitor issue seems to affect the early Mk1, Mk2 and Mk3 more than the 97-2000 Mk4 or series 2a (the cutting out issue is a Mk3 thing)
Whether this is simply down to age because of the capacitor type used I don't know but I suspect that it is down to age and the capacitor type used, probably the 97-2000 models will start to show signs of capacitor issues but maybe not as bad as the earlier cars.
I know of a few series 2a 97-2000 LS400's that have had bad caps on the ECU's.
The design on the ECU's changed for the 97-2000 VVTi models, they went from a dual board with a big ribbon connector on the earlier cars to a single more complicated multi layer board for the 97-2000 models. Maybe the VVTi model ECU's are better regarding the capacitor issue. However, if you read the topic/s below it's a case of 'when' not 'if' the capacitor issue will occur on the LS400 for all models. The caps go bad without leaking and go bad with leaking and can ruin the pcb/ecu.

In my case on my 98 VVti, I haven't experienced any issues that I know of. However, Techstream diags won't do a health check on all modules on the car. It will do a health check on individual or a few of the modules ok, I haven't used it a lot but when I have used Techstream it's a bit flakey and intermittent. Maybe it does have capacitor issues and I don't know about it.
I'm doing this for prevention and as a bit of a project, that's all. Having the ECU rebuilt by a real expert in this field of expertise will prevent any issues, that's the most important bit, bonus may be that the car will run better. I'm told reports are that after the ECU is rebuilt (by 'Lscowboyls'), low down torque is better and mpg is significantly better. If that's the case then it will be a nice bonus. I've conversed with 'Lscowboyls' a lot for this, he is the best person to do this and it's not just my opinion if you do a web search or some research.

Useful links:

https://www.clublexus.com/forums/ls-1st-and-2nd-gen-1990-2000/656360-all-my-crazy-lexus-issues-solved-ecu-leaking-capacitor.html

Link to 'LscowboyLS' posts and there is a post about how to check if you have the capacitor issues. A bit technical and involved but the information is there.

https://www.clublexus.com/forums/search.php?searchid=25933349

Tinonline · May 11, 2023

10 minutes ago, Razor61 said:

The capacitor issue seems to affect the early Mk1, Mk2 and Mk3 more than the 97-2000 Mk4 or series 2a (the cutting out issue is a Mk3 thing)
Whether this is simply down to age because of the capacitor type used I don't know but I suspect that it is down to age and the capacitor type used, probably the 97-2000 models will start to show signs of capacitor issues but maybe not as bad as the earlier cars.
I know of a few series 2a 97-2000 LS400's that have had bad caps on the ECU's.
The design on the ECU's changed for the 97-2000 VVTi models, they went from a dual board with a big ribbon connector on the earlier cars to a single more complicated multi layer board for the 97-2000 models. Maybe the VVTi model ECU's are better regarding the capacitor issue. However, if you read the topic/s below it's a case of 'when' not 'if' the capacitor issue will occur on the LS400 for all models. The caps go bad without leaking and go bad with leaking and can ruin the pcb/ecu.

In my case on my 98 VVti, I haven't experienced any issues that I know of. However, Techstream diags won't do a health check on all modules on the car. It will do a health check on individual or a few of the modules ok, I haven't used it a lot but when I have used Techstream it's a bit flakey and intermittent. Maybe it does have capacitor issues and I don't know about it.
I'm doing this for prevention and as a bit of a project, that's all. Having the ECU rebuilt by a real expert in this field of expertise will prevent any issues, that's the most important bit, bonus may be that the car will run better. I'm told reports are that after the ECU is rebuilt (by 'Lscowboyls'), low down torque is better and mpg is significantly better. If that's the case then it will be a nice bonus. I've conversed with 'Lscowboyls' a lot for this, he is the best person to do this and it's not just my opinion if you do a web search or some research.

Useful links:

https://www.clublexus.com/forums/ls-1st-and-2nd-gen-1990-2000/656360-all-my-crazy-lexus-issues-solved-ecu-leaking-capacitor.html

Link to 'LscowboyLS' posts and there is a post about how to check if you have the capacitor issues. A bit technical and involved but the information is there.

https://www.clublexus.com/forums/search.php?searchid=25933349

Hi

Forgive me for asking…what’s the cost implication of such a repair?

Simon

Razor61 · May 11, 2023

2 hours ago, Tinonline said:

Hi

Forgive me for asking…what’s the cost implication of such a repair?

Simon

I don't know exactly yet, I need to take the existing ECU out the car and ship it the USA. Cost for a standard ECU rebuild by the guy I'm using is around $400 plus the shipping cost to send it back to me and approx £40-£50 for me to ship to him. I'd guess at around $500 - $600 so about £500.
If an owner plans on keeping their LS400 long term it makes sense to get the ECU rebuilt and it will be good for 20 years, just my opinion of course.
Don't want to be without the car for a few weeks hence the plan to install a used ECU that will work while the original is being rebuilt. Probably won't do that now and will just take the car off the road for a few weeks, take a weeks holiday in that time and work on any rusty bits underneath the car. There's not much but I want to at least remove the panels covering the cills and treat/paint all the rusty bits on the cill seams around the jacking points.

Tinonline · May 11, 2023

That’s a plan…obviously you’ve checked no one in UK could do an ecu rebuild…must be some magician tucked away…🙂

Razor61 · May 11, 2023

2 hours ago, Tinonline said:

That’s a plan…obviously you’ve checked no one in UK could do an ecu rebuild…must be some magician tucked away…🙂

There are companies that will replace the caps but they need to be the ones specified by LScowboyLS which are not readily available in the UK, I ordered lots from DigiKey in the USA. I still have them all but I won’t be using them.

Bill aka LScowboyLS has done this work for years and doesn’t just replace the caps with the ones I’ve bought and anyone else can buy, although they are are a vast improvement on the originals. He uses special or super caps which he has researched along with a specialist in Japan, no info on what they are apart from that. All the work is to Denso spec with care and attention using, for example, a microscope to check the board and soldering. I’m told and read that you cannot tell at all that any work has been done but it has. Of course the proof of the pudding will be when the job has been done and I’m repeating what I’ve been told or read.
One other thing, there is a cap on the VVTi ECU that is bi-polar which means it doesn’t have a + positive or a - negative as normal. Caps normally have a stripe or indicator to show the polarity. When I tried replacing the caps myself I drew a diagram of the caps on the board, polarity, where they are and what value, i.e. C101 - 10uf 50v. I noticed one cap without a polarity indicator, didn’t think much of it and marked the polarity as all the rest cos they all faced the same way but during my correspondence with Bill I sent a picture of the diagram I’d made. He said I’d got some of the values are wrong, I checked and said ‘I don’t think I have’. He then said that it wasn’t the values but one of the caps is a bi-polar cap, my memory kicked in from years ago repairing TV/audio/video and the penny dropped. That convinced me he was the right guy to do the job.
After all that, the point I’m trying to make is that on the VVTi ECU there is more to it than just replacing the caps. The board needs to be checked for any leakage (however small), repair board if needed and it can be done, replace caps, soldering to Denso spec, clean to as new condition and check all the work which is a brief outline of what Bill does. The earlier ECU’s are more straightforward I think and replacing the caps is probably not a big deal and I could probably do them no problem, the VVTi one though I really struggled as mentioned earlier. I practiced on a scrap computer pcb beforehand and didn’t have an issue, there is something about the VVTi ECU that’s more difficult to work on and Bill did say that.

Razor61 · May 11, 2023

The immobiliser chip ‘project’ continues…….
Yesterday I removed the immo chip from the spare ECU, stuck it in the EEPROM programmer and successfully read the ‘key’ data and saved the ‘dump’ file (which is basically all the data in a file format as a backup and can be edited)
Today I edited the dump file mentioned above to remove all the ‘key’ data and left the ‘dealer codes’ or something similar.
Saved the dump file with an appropriate name and then wrote or programmed the new data to the immo EEPROM. Disconnected everything, reconnected everything and then read the data from the chip to make sure it had actually worked. All good and chuffed that an old dog can learn new tricks🤣
The ‘new’ plan, now I have a reset immo chip, is to solder it back on the spare ECU, put a new cap where I’d just remove a cap and left it, stick the spare ECU in the car and see if the ECU is in ‘key’ programming mode as it should be. If it is I’ll programme in 2 of my existing keys, 1 master and one valet, and another I bought off eBay as a master that hasn’t been programmed at all and see if the car will start and run. If that’s successful I’ll leave the spare ECU in the car and send the original to Bill to rebuild it. Once I have the rebuilt ECU back I’ll fit it, the spare ECU I will then put up for sale with a master key, the one from eBay mentioned above, so no need to remove the immo chip and reprogram………simples😀
But of course all that may change again.

Tinonline · May 11, 2023

45 minutes ago, Razor61 said:

The immobiliser chip ‘project’ continues…….
Yesterday I removed the immo chip from the spare ECU, stuck it in the EEPROM programmer and successfully read the ‘key’ data and saved the ‘dump’ file (which is basically all the data in a file format as a backup and can be edited)
Today I edited the dump file mentioned above to remove all the ‘key’ data and left the ‘dealer codes’ or something similar.
Saved the dump file with an appropriate name and then wrote or programmed the new data to the immo EEPROM. Disconnected everything, reconnected everything and then read the data from the chip to make sure it had actually worked. All good and chuffed that an old dog can learn new tricks😀
The ‘new’ plan, now I have a reset immo chip, is to solder it back on the spare ECU, put a new cap where I’d just remove a cap and left it, stick the spare ECU in the car and see if the ECU is in ‘key’ programming mode as it should be. If it is I’ll programme in 2 of my existing keys, 1 master and one valet, and another I bought off eBay as a master that hasn’t been programmed at all and see if the car will start and run. If that’s successful I’ll leave the spare ECU in the car and send the original to Bill to rebuild it. Once I have the rebuilt ECU back I’ll fit it, the spare ECU I will then put up for sale with a master key, the one from eBay mentioned above, so no need to remove the immo chip and reprogram………simples😀
But of course all that may change again.

OK you are a genius and consummate problem solver…doesn’t give up…take my hat off to you…👍👏👏👏

Razor61 · May 12, 2023

8 hours ago, Tinonline said:

OK you are a genius and consummate problem solver…doesn’t give up…take my hat off to you…👍👏👏👏

Thank you Sir
By the way, I visited Lexus Bolton yesterday and asked if they could reset the immobiliser. Answer was no, you need a master key.

Razor61 · May 13, 2023

The ‘new’ plan worked like a dream apart from the eBay key. Soldered the re programmed immobiliser EEPROM to the board of the spare ECU, I practiced on a scrap pc board and all good. When it came to the spare ECU I was shaking like a leaf😀
Calmed down enough to get it soldered, cleaned up the flux and reassembled the unit.
Disconnected Battery on the car and removed the ECU, installed the spare ECU, connected the Battery and it was in programming mode for the ‘keys’.
Programmed my existing 3 x keys but the eBay key didn’t work.
Inserted one of my original keys and it started no problem, tried the other 2 keys and they worked as well. The eBay key I’ll have a go at again, not hopeful though.

All things considered I’m very happy, I can send the original ECU from the car to be rebuilt and still drive the car.
I’ll update this bit again when the ECU has been rebuilt and installed back in the car.
When I get some plugs to power up the spare cluster on a bench, I’ll have a go at the mileage correction.