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Yes, it could have caused damage outside of the ECU, it really depends on what circuits that burnout leads to. If possible, try to follow the traces on the circuit board to identify which pin connections those burned out spots lead to, then use a pinout diagram to identify the circuits that need further inspection.
After this, do you really want to resolder a chip and risk doing this again? The data on that immobilizer may or may not be corrupted now, the only way to know for sure is to read the data on IC900. If it's good, you can rewrite it to a replacement ECU. If it's bad, virginize IC900 or use a direct input method with your existing keys. We can handle this part for you if you're interested.
I got my original ecu back and it isn't pretty. I must have shorted some of the traces with my poor soldering skills.
I'm guessing this board is not repairable - so two areas of questions...
1) Could this short also have impacted other components of the electrical system that would keep my replacement ecu from communicating? Any suggestions on where to start looking? Does anyone have an picture of the wiring harness components? I've downloaded a bunch of pdfs from the Toyota service manual portal but I'm having a hard time navigating them to find the right information.
2) Can the immobilizer chip be moved from the old ecu to the new one to match the current keys? Is there a link on how to do that?
Thanks,
The burnt area is a voltage regulator circuit which supplies the regulated 5V DC to processors and sensors. The board is carbonized badly and it is beyond the repairable level, to my eyes. Without analysing and checking the board precisely myself, I have no idea to judge how much other components and related/connected other circuits are impacted.
If I were you, I'd simply try reading the data stored in the IC900 which is printed 93C56 and write the contents to another working ECU's chip using a method as is explained here.
Toyota's immobilizer system in those days uses the EEPROM chip 93C56 mostly and the reference number IC900 is commonly used. Actually a 1UZ-FE VVT-i engine's ECU uses the same reference number/chip and I'm sure you can find it on the board easily. It is located near the other side of the corner.
If you were not comfortable to do above, this would be another way to swap the immobilizer chip using a soldering iron like this below.
Above both methods are based on a expectation that the chip is alive. As far as I know, the chip 93C56 is rather strong against the over voltage. It also needs special sequence to rewrite the data. So I guess the chip is still alive and the stored data is not corrupted.
I hope you succeed to revive your LS400. Good luck.
Your original immobilizer eeprom is most likely ok. They are tough. It is easy to swap them. The best way if you dont have soldering skills or the equipment would be to find a computer repair person that can. It is also easy to read your key codes off your old eeprom and write them to a new one. If you were local to me I would be happy to do this for you for free as it is a simple operation.
Edit to add:
It also can be possible to "piggyback" ecus. You might be able to plug all the connectors into the new ecu, and plug the immobilizer connector into the old one and run both ecus
Thanks for all the replies! My soldering skills are actually pretty good - I was working with a bad tip on a gun when I swapped in all the new capacitors. I'll get a different iron for small work next time around. I'll start working on finding what else in the wiring is keeping the ecu from communicating properly. Then I'll move on to fixing the immobilizer codes. Looking forward to getting this land yacht running again.
Finally got some time to dig a little deeper on identifying the circuits outside of the ecu causing my issues - which is - I can't communicate with the replacement ecu.
I identified the soldering point which was most likely the source of the original short on the board and lead to its eventual demise (red circle on board). I figure anything associated with the grounding trace surrounding transistor R280 is a likely culprit. I found two such solder points that lead to several pins.
The first (blue circle) leads to one of the circuits in the E3 Electronically Controlled Transmission Solenoid.
The second (yellow/black circle) leads to 4 pins - 3 of which all go to the same ground point on the engine. The fourth is a shielding circuit for some leads going to the T22 Throttle Control Motor and Clutch.
I'm really hoping the ground circuit has somehow gone bad - hopefully not deep in the wiring harness. Now I just need to head out into the not-quite-freezing rain and see if I can locate this ground terminal on the LH cylinder head. Trying to get myself psyched up for that.
11-17-18, 07:47 AM
The data on that immobilizer may or may not be corrupted now, the only way to know for sure is to read the data on IC900. If it's good, you can rewrite it to a replacement ECU. If it's bad, virginize IC900 or use a direct input method with your existing keys. We can handle this part for you if you're interested.
