DIESEL EMISSIONS
Common Causes
Let’s look at some common causes that prevent regeneration or increase the frequency of regeneration.
1. The HD doser should be checked for proper operation. If the hydrocarbon doser fails, diesel fuel will not be injected into the exhaust stream and the engine will fail to regenerate.
2.
If either of the DPF pressure sensors malfunction, the aftertreatment control module or the Engine Control Unit (ECU) will receive false readings and could initiate frequent regenerations.
3. Exhaust Gas Recirculation fault codes can interfere with the regeneration process. Any fault codes related to the EGR system will cancel a regeneration.
4. DOC failure, commonly referred to as face plugging, will interfere with the regeneration process. The injected diesel fuel uses the diesel oxidation catalyst to raise the temperature of the exhaust and start the process of burning the soot in the Diesel Particulate Filter (DPF). Face plugging of a DOC can occur when a vehicle is used on short trips and or stop and go traffic. It is important that an engine is allowed to get to the correct temperature to insure DOC face plugging does not occur.
5. Diesel Particulate Filter plugging can happen which will prevent a satisfactory regeneration. Regeneration times may be longer with poor results. This usually occurs when a DPF has not been removed for routine service by either baking and
blowing or an aqueous cleaning which restores the filter to at least 95% of its new capacity.
6. Temperature sensors being faulty will stop the regeneration process. The readings from these sensors give an indication of how the DPF system is operating.
7. Variable Geometry Turbo failures can prevent regenerations from being completed as not enough heat is generated to complete the process.
8. Engine fault codes related to temperature, emissions, pressures, turbos, boost, and other components can prevent the regeneration process from occurring.
9. Faulty electrical components like plugs and wires can also prevent regeneration. Sensors may not be malfunctioning but the ECM or other related computers will receive incorrect values due to the wiring harness being defective.
It becomes evident pretty quickly that the newer emissions systems with diesel particulate filters are much more sophisticated than earlier diesel engines. It is imperative that the emissions system be properly diagnosed and repaired when the regeneration process fails. Usually it is less expensive to repair the system before a DOC and DPF are compromised beyond servicing, requiring replacement.
The schematic above will give you an indication of the amount of technology that goes into controlling an exhaust system so it meets current Environmental Protection Agency regulations.
January/February 2022| THE COOLING JOURNAL | 23
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