92 Subaru check engine light won't go off

my 92 subaru check engine light has been on for months. I took it to my mostly-trusted mechanic. He hooked it up to the computer and the car did not give any codes. He reset the light, but it came right back on when started. I am wondering about the coolant temp sensor but I would expect that would give a code. Why won’t a check engine light give a code?

You are going to have to give your mechanic a lot of “lee way” here as the diagnostic system in 92 was rather primitive and then to also be working with a earlier Subaru is a “double wammy”. You are going to have to be patient, eary diagnostic systems were often more trouble than the information they gave you was a benifit.

You read the codes by counting the flashes of the LED in the ECU when you connect the black wires under the dash. If there are truely no codes set then there is a fault in the CEL light circuit inside the ECU. Sometimes the IC fails and needs to be replaced.

Thanks for the info. For the time being I’ll get the black electrical tape out.