usually the diagnosis plug by the battery is for the analyser (prob spelt that wrong) and you can short two of the pins out to clear the error code and remove the management light if I remember, you can also just disconnect the battery for 20 seconds to do this. ive found with Toyotas that generally theres two type of codes, one which I call a spike code, which is like a flash error that the ecu/truck has detected but managed to correct itself and therefore truck runs fine but the mil light stays lit, and then theres an active code where the truck has a genuine error and the ecu/truck cant correct itself and the mil light stays lit and the truck runs faulty. easiest way is disconnect battery for 20secs or more then reconnect, start truck up and see if mil light comes back on, if the mil light doesn't come on straight away then run the truck around, full throttle and under load etc to see if comes on, if doesn't then its just a spike code, if it does, note when it appears i.e full throttle etc and at least you have a starting area to look at.