Check engine light light came on for the first time ever in 24 years and 227k miles set a code 41. I have access to alldata, the diag flow chart is a bit confusing. If I follow it it tells me the PCM is bad. The field terminals nuts are rusty. Does any body know what I should have for voltage when the engine is running at the field terminals? I'm gonna have the alternator tested ASAP. Has anybody had to replace their PCM for this?