Shooter Barnwell
Member
First time poster, I’m a diesel tech who’s been out working on a cat 279d. The customer had another person install a new coupling between the motor and hyd pump, after this was done the machine wouldn’t start by the key. I was then called, and let it be known I’m not a CAT fan. I tested every safety switch, they’re all functioning. Tested power to the relay, good. Swapped relays as i know they’re a problem with a non oem relay, no change. I’ve ohmed the green and white wire from the ecm to the relay and they’re good. I hooked my meter to the green signal wire coming from the ecm to the relay, with key on and all safety switches down I’m only getting .14v, now i understand cat uses the relay signal and ground to communicate with the ecm that safety’s are down and it’s good to start. What i don’t know is what that voltage is supposed to read, I’m assuming my ecm is fried on this leg, any insight would be helpful