LS400 ECU replacement and capacitor issue information

[Razor61]

I know there are other topics and posts about this but I wanted to collate all the information I have gathered in one place.

If you need to replace the ECU on your LS400 or suspect you have a bad ECU, this information will hopefully help and is correct to the best of my knowledge.
Normally this is needed due to a bad ECU and is normally caused by bad or leaking capacitors, well documented here and other places for the reasons why.
If you are not experiencing any issues that you know of, having the ECU rebuilt correctly with the correct replacement capacitors is a good idea in my view. Your car may be off the road for a while but  'An ounce prevention is better than a pound of cure'.......................as the saying goes.
All this information is a combination of my experiences and information I've gathered from various sources. If you think anything is not correct then let me know and I'll update this.

ECU replacement:

Model years 1989 - 1994 aka Mk1/Mk2 or series 1 and series 1a - ECU is a 'dual board' design, can be swopped out and should just work. If the replacement ECU is in a working state.
I have been told by an 'expert' in rebuilding ECU's that the capacitors just go bad and don't normally leak causing PCB damage and corrosion.
Replacing the capacitors correctly and with the correct type and quality is normally all that is needed. Once rebuilt correctly with the correct replacement capacitors the ECU should last a long time.
This can be a DIY job if you know what you are doing with a soldering iron etc. but I would recommend an expert do this.


Model years 1994 - 1997 aka Mk3 or series 2 - ECU is a 'dual board' design, can be swopped out and should just work, I have done this with no issues. If you can find a replacement and the replacement ECU is in a working state of course.
I have been told by an 'expert' in rebuilding ECU's, and reading information on forums, that these ECU's (there are quite a few different types) are the most common for bad and especially leaking capacitors causing PCB damage.
If your car is experiencing strange issues relating to bad capacitors then it may be too late and the PCB has been damaged too much by capacitor leakage. The only way to find out is to remove the ECU and have it checked out.
The ECU PCB/Tracks may be fixable by an expert/someone who knows what they are doing and then replace the capacitors.
This can be a DIY job if you know what you are doing with soldering iron etc. and the PCB isn't damaged by leaking capacitors but I would still recommend an expert check it all out and do this. 

Model years 1997 - 2000 aka Mk4 or series 2a - ECU is a 'single board' design and cannot be just be swopped out and will work. This is due to the immobiliser that is integrated into the ECU, previous years did not have the immobiliser integrated into the ECU.
This model/version of ECU's suffer from bad capacitors and capacitor leakage and can cause damage to the PCB/Tracks. I have been told by an 'expert' in rebuilding ECU's that there normally 'is' capacitor leakage but it's not always easily visible and needs examining carefully to find it.
These ECU's are more difficult to work on to replace the capacitors, I know from experience. Because the PCB is a 'single board' design and has more 'layers' than the earlier 'dual board' design ECU's, the amount of copper in the tracks acts as a big 'heat sink' which soaks up the heat from the soldering iron. Replacing the capacitors is best left to an expert who has the knowledge and equipment to deal with it. Maybe pre heating the complete board will help with this but what temperature to heat the board to safely I don't know but an 'expert' will.
If you can find a replacement ECU, ideally one that has been rebuilt with new capacitors or you have it rebuilt with new capacitors and any damage repaired, and you have a matching 'master' key fob then you can swop it out. You can use the matching master key 'innards' and add your existing master keys to the ECU/Immobiliser.

If you have a replacement ECU without a matching 'master' key fob then there are some options.

1. remove the immobiliser chip or IC (IC900) from your original ECU and replace IC900 on your replacement ECU with it, basically swop over the immobiliser chip or IC (IC900)and your existing keys should just wok. Not a DIY job for a novice, you need good soldering skills with surface mount components to remove the chip without damaging the chip or the board solder pads. Better to have an 'expert' do it for you unless you know what you're doing.

2. remove the immobiliser chip or IC (IC900) from your replacement ECU and reprogram the chip so all the 'key' information is removed and is in 'Auto Programming Mode' as if it is a 'brand new' ECU. Fit the replacement ECU and your existing keys will be programmed to the ECU following the instructions in the video below.
I found this video to be the most useful for this:   https://youtu.be/OxvMeMo-j_A
As in option 1 above, not a DIY job for a novice, you need good soldering skills with surface mount components to remove the chip without damaging the chip or the board solder pads plus an EEPROM programmer and software. Better to have an 'expert' do all this for you unless you know what you're doing.
I have used this method on my 1998 LS400 with a replacement ECU that didn't have a matching 'master' key and it works, replacement ECU is in the car and working with the original ECU on it's way to the USA to be rebuilt.

I hope you find this information useful.

[Howplum]

Thank you Paul for going to the trouble of compiling the information. Very useful.

[Malc1]

might Mods pin this post to the top of the Ls400 forum page do you think  !

Malc

[Howplum]

Paul, perhaps it's possible to create a topic under Lexus How-to Guides and copy and paste your text.

[Razor61]

4 hours ago, Howplum said:

Paul, perhaps it's possible to create a topic under Lexus How-to Guides and copy and paste your text.

I started to do exactly that but changed my mind, I figured this is more of an ‘information’ thing. I will create a How-to guide for the EEPROM chip removal, not soldering, and programming though.

[Razor61]

Update to this.

Tonight I replaced the capacitors on an early LS400 ECU part# 89661-50050
The ECU is a ‘dual board’ type and it wasn’t a problem for me to replace the capacitors being careful and figuring out the best way to do it. Vastly different to the 97-2000 single board ECU which is a different beast.
Having a thin stainless pin of some sort is essential to ‘make’ the holes through the board to install the new caps, as described in other posts, but getting one is another story. I found some safety pins but they were not stainless, I used a magnet to find out. In the end I found a thin power washer nozzle cleaner thing, stainless and the perfect size. 
Good idea is to watch videos from Mr Solder Fix on YouTube.
if you are going to attempt this yourself this is a good tip which I saw on a Mr Solder Fix video. Once you remove the capacitor and ‘make’ the holes in the board, fit the capacitor - tack one leg - clip the legs to the correct length - apply some flux to the pads - solder the ‘un tacked’ leg - then solder the other leg - when soldering count for 3 seconds while applying the solder - check the other side of the board to check the solder has run through ok - if not apply the soldering iron again for 2-3 seconds and check again. Clipping the legs reduces the amount of metal to absorb the heat from your soldering iron, just my theory but Mr Solder Fix does this.

[Supafly]

Thank you for taking the time to document all of this 🙂 and for the tips too, they're very useful.

[Razor61]

8 hours ago, Supafly said:

Thank you for taking the time to document all of this 🙂 and for the tips too, they're very useful.

You’re welcome, the replacement ECU I installed in the car performs better than the ECU from the car that I sent to Bill (LScowboyLS guy) for the rebuild. I didn’t want to say anything until I was sure but the car definitely performs better and not just slightly better, quicker off the mark, more powerful and shifts gears better. Caps are not ‘as bad’ I presume. Seems to start better as well but I can’t be 100% about that. Looking forward to fitting the rebuilt ECU and see how much it improves the running of the car.
It’s difficult to ascertain if the car is performing and running as it should because you can’t compare it to a brand new LS400, I’ve not driven a new LS400 or very new LS400.
Strange thing is that the MPG on a long run at motorway speeds is worse but the MPG going to work and back is better.
This illustrates the differences between the same ECU’s due to varying degrees of the capacitors efficiency and how well they are working or not working.

[Supafly]

I wonder, could the performance difference be due to the 'adaptations' from when the replacement ECU was in its previous car?

[Razor61]

6 hours ago, Supafly said:

I wonder, could the performance difference be due to the 'adaptations' from when the replacement ECU was in its previous car?

Nope, I've had the Battery disconnected lots of times when testing the spare clusters and audio/satnav units plus when replacing the Yaw Sensor and for other reasons.
So the 'adaptations' have been reset multiple times on the old ECU.
Normally I would just reconnect the Battery and away I go but I found a TSB outlining how to reset the 'adaptations' and the correct method to help/speed up the learning process.
When I fit the rebuilt ECU I'll follow the TSB instructions.

ECU_Clear_Learning_memory.pdf

[Supafly]

I like the simplicity or reset procedure 2 😀

My understanding was that there are two sets of adaptations, 1 short term (volatile) and the other long term (persistent - written to memory and unaffected by power loss).

The TSB (thank you 🙂 ) seems to show that it will all be reset.  I might try it when I next service the car...

[Razor61]

9 hours ago, Supafly said:

I like the simplicity or reset procedure 2 😀

My understanding was that there are two sets of adaptations, 1 short term (volatile) and the other long term (persistent - written to memory and unaffected by power loss).

The TSB (thank you 🙂 ) seems to show that it will all be reset.  I might try it when I next service the car...

Ah, I see what you mean about the 2 sets of adaptations. It’s possible I suppose, there is a clear memory function in Techstream so will try that.