A 2016 Volvo V90 came into the bay with a P20EE00 code and a massive smoking problem whenever the technician forced a DPF regeneration via VIDA. The scan tool showed low soot accumulation, making the heavy smoke completely contradictory. In the diagnostic platform we build, I see how these conflicting symptoms trip up a standard diagnostic process.
The Contradiction in the Exhaust
The technician noted that the car smoked heavily during a forced regeneration, yet VIDA reported a small amount of soot. The P20EE00 code points to SCR NOx efficiency below the threshold. If the filter is not blocked, the smoke has to come from an external fuel or chemical source entering the exhaust stream.
Leaking Injectors and Oil Dilution
Our engine ranked a leaking or dripping fuel injector as the most likely cause at 82 percent. On Volvo's 2.0D VEA engine, fuel for DPF regeneration is added via late post-injection directly through the common rail injectors. If an injector leaks mechanically or drips when closed, raw diesel washes past the piston rings into the oil pan.
During a forced regeneration, excess diesel is injected late in the cycle. If an injector is already over-fueling, the diesel boils in the exhaust and DPF instead of vaporizing. This generates enormous amounts of thick smoke despite the low calculated soot. The unburned hydrocarbons then coat the SCR catalyst pores, disrupting the NOx sensors and triggering the P20EE00. The right tests here are a return flow measurement, cylinder balancing in VIDA, and checking the engine oil for diesel dilution.
The Crankcase Fume Loop
Ranked next at 74 percent is a saturated crankcase from aborted regenerations. Short trips prevent the exhaust from reaching the temperatures needed for passive regeneration. The engine control module initiates active regenerations that get repeatedly cut off when the engine shuts down. Unvaporized diesel accumulates in the oil pan.
When the technician runs a stationary forced regeneration with VIDA, the engine and oil pan get very hot. The diesel in the oil evaporates and gets sucked through the PCV system directly into the turbo inlet. The engine burns its own diesel fumes, causing massive smoke independent of the actual soot level. Checking the PCV hoses for liquid fuel and reading the regeneration intervals in VIDA will confirm this.
AdBlue Pyrolysis and Melted Substrates
We also saw a 68 percent probability for a leaking or crystallized AdBlue dosing valve. If the DEF injector sticks open, concentrated urea drops into the exhaust mixer. Forced DPF regenerations push exhaust temperatures to between 550 and 650 degrees Celsius. The pooled urea rapidly boils, creating thick white smoke with a sharp ammonia smell.
Finally, a cracked DPF substrate ranked at 61 percent. Previous severe oil dilution can cause uncontrolled localized heating over 850 to 1000 degrees Celsius, melting the DPF core. The differential pressure drops, tricking VIDA into calculating low soot, but soot blows right through during regeneration and coats the SCR. A tailpipe wipe test or DPF endoscopy will catch this.
Next Steps for the Bay
When a vehicle presents a P20EE00 code alongside heavy regeneration smoke and low calculated soot, do not immediately condemn the exhaust components. Check the engine oil level for diesel dilution and inspect the PCV hoses. Testing the injectors first will often reveal the root cause before you spend time tearing down the aftertreatment system. Let me know if your workshop has seen this specific failure loop on the VEA engine.
Reference pages for the codes in this article
- P20EE, what we measure for this code across real diagnostics