It is difficult if not impossible sometimes to tell you anything without some data & a scanner. That said any other running info you can provide may allow me to give you a couple possibilities that may or may not be the culprit (engine models, hours, speed, rpms, conditions, etc when the alarm went off). Other wise there is a long list for sure of reasons that the alarm may go off.. Jamie / Lakeside
BTW, I understand about the coin these days as well as anybody, but a good tech is worth their pay, as they can at times help keep you from needing a more costly repair..