Can't reprogram remote locking to Yaris MK1 key? Read this.

May 8, 2023

Had a spare key for my Yaris 2002 (MK1) which would unlock and start the car manually (as immobilizer chip was fine) but the remote central locking would not work. A light would show on the fob when buttons were pressed but nothing would happen. This key uses a VALEO type board. Battery measured fine on the multi-meter.

Tried reprogramming the remote locking using one of the guides online (open driver door and close twice, etc) and my fully working FOB. However, once I got to the part where the car door locks cycle, pressing unlock and lock buttons on the bad FOB would do elicit no response from the car. It's kind of like the key wasn't able to send any signals.

Diagnosing further, I found that the culprit was the big flash chip, labelled "JAPAN" on the VALEO board. I assume this chip had become damaged because of one of: water damage, heat, mechanical damage, age, etc. There was no visible damage to the outside of the chip though, so nothing to indicate it was damaged. I got to this conclusion by hot air soldering this chip on and off a confirmed working key board and testing various configurations, eliminating other factors, etc.

If you have this problem while reprogramming a MK1 VALEO fob, there is a way you can regain central remote locking functionality. Firstly, get another VALEO board from eBay etc. Simply open your fob up and replace the board. Then, reprogramming the central locking using one of the numerous guides online should work. There's no harm in doing this. If your original (i.e. programmed) immobilizer chip is still wedged in your key fob frame, it should start the car up regardless of what board is the FOB. You could also just hot air solder the "JAPAN" flash chip from the new board to your board, but it's easier just to replace the board (if the rest of the new board is working fine).

Just sharing in case it helps someone as I've been trying to figure this out for ages and couldn't find anything on a google.