Daughter called me to say she was broke down on side of road.

Truck wouldn't crank and the lights on dash indicated limp mode. I had her try to crank the truck, but would not crank. I heard a buzzing noise coming from the coolant reservoir area but it could be the reservoir because there isn't anything there to buzz. I knocked it around and then the sound went off.

I have no idea what could have been buzzing. Had her turn the AC off and the truck stayed running. At least got to drive it home.

What would the AC have to do with the truck going into limp mode and then shutting off. Or is there something else under the coolant reservoir that can be buzzing and causing the engine to die?

 

Maybe a relay in the fusebox chattering?

 

If the battery is low on charge, Discos do weird things. Hook the battery up to a charger overnight to see if that clears any issues before moving on to more serious troubleshooting.

 

Most of my limp mode experiences have resulted from the battery clamps being loose on the battery posts. Have had to use battery post shims to ensure a tight connection. Even if the battery clamp is relatively tight, if it has any give or wobble at all it can cause a no-start or limp mode situation, if it's already started and then bumped loose, both have happened to me. Also ditto Brandon318, a full battery charge is also a good idea.

 

Just had the battery clamps replaced, but will check again

 

Well, I found the buzzing noise coming from Relay 9 under the hood. It would buzz, and I would not start the truck. I tapped it with a screwdriver and make it stop buzzing, and then it would start. I have also had a parasitic draw I have been trying to track down. This could be the source of all my issues.

 

Glad you found it!

 

got a replacement Relay, installed and did not fix the problem. Bad Fuse Box?

 

I have the fuse box out. Is there anything obvious to look for?