Hi there,
I've had the same problem talking to my '98 LS400 Mk4. My research came to the following conclusion:
On a UK LS400, the port that looks like 'ODB-II' under the dash is not in fact 'ODB-II'. It is referred to by Toyota as 'DLC3'. It is possible to interrogate the ECU using the following method from the Celsior manual (it works on my '98, anyway):
- Place car in Park, ensure A/C is off
- Short between pins 4 and 13 on the connector socket (as per picture) - you can use a paperclip
- Turn ignition switch to 'ON' (do not start the car). 'DIAG' is displayed on the LCD display below the speedo
- Press the 'Function' button on steering wheel once - display changes to 'EFI'. If there are any EFI warning codes, it will then display 'EFI NG' and any codes in sequence; otherwise 'EFI OK' is displayed. If 'EFI --' or 'EFI E' appears then the ECU may be partially dead.
- Press the 'Function' button again - display changes to 'VSC' - this will display the codes for VSC (if any) in the same manner
You can use Google to find lists that will tell you what the fault codes mean.
I hope that helps!
Dan