Hope this is the correct place to post.. 85 TA 5.0 TPI LB9.. check engine light comes on once in a while and drives rough while its on but next time i start it the light won't come on and it'll drive fine. When the light's not on i can't get any codes with the paper clip.. only 12 repeating.. how do i find out what's causing the light to occasionally come on?

 

Hello, If I'm not mistaken... it has to be operating under the conditions that set the code for more than 20 or 30 seconds or something before it's stored to ECM memory. Shut off & restart before code is stored & boom all you're getting is Code 12. Good luck!

 

Ive had codes stored in my 67 for things that arised for less tan 30 seconds. Im not sure if the 85 is different though.

Did you leave the clip in and let it flash past the cde 12? it will always flash code 12 first before the next code

 

yes it flashed 12 three times.. then 3 more times. No other codes. I still can't get the light to come back on.

 

It could be like 92 RS said where wither the older ecms need so many seconds of the actual problem, or certain problems will require this,


Is the light flashing or steady when on?


If anything, Id disconnect the battery to reset everything and see if the problem itself comes back.