Truck Repair: n 14 cummins derate, pressure coolant, coolant temp

Question
Hi I have 2000 n 14 cummins celect plus engine that is driving me crazy. When driving for a hour or so the check engine light comes on and derates the engine to 85 km per hour and 1550 rpm now this light starts intermittently then as you continue to drive it stays on longer and longer. I have changed all sensors, I have also put a piece on the alternator to prevent fm frequency as suggested by a delco rep. If anyone has any new ideas please help this thing is making me nuts

Answer
Hi James,
first things first, unless we know what code is causing the CEL (check engine light) to come on we are just guessing. you need to have the code downloaded. are your engines vitals good? oil pressure, coolant temp, oil temp, coolant level(if equiped with sensor). have the code read and we'll go from there.

matt