I drive a 2004 3500 express box truck. At 70 mph I let off the gas and the check engine light flashes, the BRAKE light comes on and the speedo starts bouncing between 80 and 40. After about 2 minutes the BRAKE light goes out, check engine stays on and speedo stops bouncing. Any ideas?

 

scan the check engine light

 

We were going to do that later this morning. I’ll post what we find.

 

Scanned it and it came back as Random misfire on 3 4 & 5.

 

P1380 rough road misfire data not available p300 random misfire

these are the codes that came back

 

What is a p1380 code

 

have you tried google?

obd-codes.com