[SOLVED] I have a 1986 iroc 5.0 TPI. When I turn the key to the on position it immediately tries to go into diagnostic mode. Usually thee fan relay keeps clicking on and off, the fan turns on and off but sometimes it will stay/latch into diagnostic mode and I'll get code 12. I've tried starting the car but it will shut right back off. Sometimes if I turn the key on and off it will work fine and not try to go into diagnostic mode. Is this a relay or resistor issue or is the ecm going bad? How can I test this?

 

Sounds like the ecm is going bad, does this have a Hypertech chip in it by chance?

 

I dont think it has an aftermarket chip. I've only had the car about 6 weeks. I'll check the prom tomorrow

 

 

Everything looks factory to me. What ecms are compatible? I am finding alot of Serv num 1227195 but not 1227165. Is there a database to look these up?
Also, there is just the 1 cover panel for the memcal. Shouldn't there be another to access the chip?

 

https://www.summitracing.com/parts/aaz-77-6571
only one access cover on the 165 ecm

 

https://www.oreillyauto.com/detail/c...19367537&pos=0

 

Good to know. Thank you

 

SOLVED
I wanted to close out this thread by saying thank you to everyone for the help. I found the problem was a loose wire in one of the connections for the ecm. I took the wire out and crimped it down just a little to make better contact with the pin on the ecm. Problem solved.

 

Did you have a loose wire on the harnass or on the board of the ecm? Or were the connectors in your harnass too wide apart to make contact on the board?

I too have ECM problems...