حمولة مفرطة أو قطر

The engine genuinely working harder than its cooling and aftertreatment were sized for — towing, a full load, a long climb, or high ambient temperature. It is a condition rather than a fault, and the codes it produces are the protection systems doing their job.

Coolant and oil temperature rise, exhaust temperature rises, and the module derates to protect the engine. All of that is designed behaviour. A code that appears only while towing and never otherwise is describing the load, not a component, and the vehicle will test perfectly the following day.

The useful question is whether the load is within specification. Towing capacity, nose weight and gross train weight are stated by the manufacturer for exactly this reason, and a combination beyond them will overheat a vehicle in perfect condition. Ask what the vehicle was doing when the fault appeared. Where the load is legitimate and the vehicle still overheats, the cooling system has lost margin — a partly blocked radiator or a tired fan shows up under tow and nowhere else.