Please help!
 

I just got to work and on my way here I noticed my temp gauge on the dash was all the way up so I turned my heater on and it ran cool when up to speed and at red lights but when at red lights the heater blew cold air. I was suspecting head gaskets but there's no coolant in the oil, it looks perfect and no smoke or sweet smell from the exhaust. It is low on coolant but has been for a while. Can't find a leak anywhere. But I ran my sct to check codes and I got p0606 for bad ECM/PCM but the truck was running fine it just said it was hot. And I don't have my owners manual so I don't know which fuses to check. Any help is much appreciated

Add some coolant, see if that solves the problem. If there's no leaks then sounds like your coolants just low. If it ain't smoking white, your head gaskets are fine. Pull your dipstick an check for a milkshake. If you got one you got a blown head gasket.

Checked the oil and it's fine. And I've had a problem with the coolant, it leaks to the point where it's just at the bottom of the degas bottle and stops there. I can't find where it's leaking but every time I fill it up it leaks back down to the bottom of the bottle. Not problems with the way it drives or anything. This is the first time I've had an overheating problem. Thank you for the rely though!

How quickly are you losing coolant? Have you had your EGR pressure tested? Or have it checked to see if it's throwing any DTC's? After working on so many of these 6.0's it can be anything causing you to lose coolant. Do the little things first, check the EGR valve and see if it's wet. Check your Degass tank for leaks to see if it burped. Have your cooling system pressure tested. Sounds to me like your having an EGR failure. Even with having the EGR unplugged sometimes it wont throw codes. You wont know until it's to late. Have it all checked out ASAP before it ends up costing you big $$$

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It only loses a little bit of coolant and then stops. It won't lose anymore after that and I can't find any leaks, I have an egr delete and I checked for dtcs and it came up as p0606 as I stated above for a bad ECM/PCM. I cleared the code and put more coolant in the truck and it drove fine on the way home so I'm about to go check it again and see what's going on