Desperate Trucker Owner.... SCR Melted

[hhow55]

However, outlet temperatures can sometimes exceed inlet temperatures ("temperature inversion") for these main reasons:

Normal during certain regeneration phases:
Soot oxidation inside the DPF is exothermic (releases heat). With high soot loading, burning soot generates additional heat, especially toward the filter's rear. This can briefly cause the outlet to read higher (e.g., 50–100°F difference), depending on soot/ash load. Sources note this as potentially normal if not excessive.

Faulty or inefficient Diesel Oxidation Catalyst (DOC):
The DOC should oxidize dosed/post-injected fuel to raise temperature before the DPF. If the DOC is clogged (e.g., face-plugged), degraded, or low-efficiency, unburned hydrocarbons pass into the DPF.
These then burn inside the DPF, creating extra heat and elevating outlet temperatures (sometimes >1200°F). Mechanics frequently diagnose this when outlet > inlet, as it indicates "raw fuel through DPF," risking damage to DPF and downstream SCR.

Excess hydrocarbons or combustibles in exhaust:
Leaking fuel injectors, overfueling, oil/coolant consumption (e.g., bad turbo seals), or dosing issues introduce extra fuel/oil into the exhaust.
This burns in the DPF, spiking outlet temperatures.

Sensor or wiring faults:
Swapped/misconnected sensors, faulty DPF inlet/outlet temperature sensors, or wiring problems can cause false readings showing inverted temperatures.

Other factors:
Partial DPF blockage increases backpressure and localized heat.
High soot loads without proper DOC function amplify exotherm in the DPF.


Normally, during active regen:

DOC outlet (DPF inlet) targets ~1000–1100°F (550–600°C).
{bad info removed by Rawze}

Persistent or extreme inversion (e.g., outlet >> inlet) usually signals a problem, often requiring DOC inspection/replacement, DPF cleaning, or diagnostics for fuel/oil entry. Monitor via scan tools during forced regen for accurate assessment.
Sourced from AI............