From Celica GT-Four / Alltrac - ST165 ST185 and ST205

ECU Error Codes

The ECU can self-diagnose many faults. Its not quite as advanced as OBDII but it gives you the basics. Find the diagnostic port (top of left hand wing in a right hand drive car) and short the TE1 and E1 terminals with something like a paperclip. Be careful not to short other terminals by accident.

Now take youre keys and without starting the car turn the ignition to ON. The ECU will now flash the engine light on the dash.

This light will flash in a sequence. A constant flash rate indicates no errors.

If you have errors present your light will flash the codes in the following fashion (* represents a flash, _ represents a pause):

_____*__*_*_____*_*_*__*_*______

This example sequence shows codes 12 and 32. If these are the only codes stored the sequence will start again at 12 until you remove the short from TE1 and E1. In order to decode these codes you need the code list. This is the same, I think, for all GT-Fours....

ECU Codes (all models)

Clearing Codes

Some codes reset themselves when you cycle the ignition (next time you turn on/off they'll vanish) but most require a reset. When you have fixed the fault, pull the 15A fuse in the engine bay fusebox, the one marked EFI. Take it out for 15 seconds and put it back in. Codes are now cleared. It might take a couple of journeys for the engine to feel fully happy again as it has some rudimentary learning procedures that it needs to do every time it is reset. You may find your car feels a lot more nippy when it is reset, even if there were no faults, it is believed that this is due to the ECU "learning" how far it can push the timing before knock occurs, when you reset it it goes to max and then dials itself back over time. Frequent resets for this reason are not advised.