Have an SCR that is plugged with Urea (DEF)?

What is DEF?

Diesel exhaust fluid (DEF) is a non-hazardous solution, which is 32.5% urea and 67.5% de-ionized water. DEF is not a fuel additive and does not come in contact with diesel. DEF is sprayed into the exhaust stream of diesel vehicles to break down dangerous NOx emissions into harmless nitrogen and water. 


Getting DEF into the fuel tank can be thousands of dollars to repair and getting diesel into the DEF tank will also be an expensive fix but not as much as DEF into the fuel tank. 


Ever run into the issue of coolant that has leaked into the DPF which has caused cracking and fouling of the DOC (diesel oxidation catalyst)? This will eventually lead to an engine failure. 


How about a fuel leak that has melted the DPF and created a need for an earlier than expected cleaning?   

One of the more common problems a fleet may encounter is face plugging of the diesel oxidation catalyst (DOC). Black deposits form when unburnt fuel is collected on the front end of the catalyst. This increases backpressure on the engine and requires exhaust gases to funnel through a smaller area than intended. As a result, the exhaust gas travels through the oxidation catalyst too quickly for processing and travels through to the particulate filter, which can become plugged prematurely. This has a domino effect which eventually lead to the failure of other components. 

 An image of a cracked Diesel Particulate Filter

A diesel particulate filter (DPF) must be cleaned.


If the filter isn’t properly cleaned, leftover ash can compete with soot for space, causing the DPF to overheat and potentially causing the substrate to crack. This will allow unfiltered exhaust gas to pass through to the SCR catalyst.


The results can include a poisoned catalyst and cracked DPF, both expensive problems to repair.