Do you have a Haynes manual? There is a procedure for getting codes. Depending on what type of connection there is, you either short together 2 terminals or 2 wires and see how many times the CEL flashes when you turn the key (to ACC I think). The CEL will flash, then pause then flash some more. The number of time it flashes the first time is the first digit of the code. The number of times it flashes the second time is the second digit....or something like that. That's what I got from reading the procedure real quick. My Rodeo has OBD II, but I'm sure some of the guys with engines that have the older DTC systems will be able to help more.