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Technical Bulletin

 

 TROUBLE SHOOTING YOUR  
DIESEL PARTICULATE FILTER (DPF)
&
 DIESEL OXIDATION CATALYST (DOC) 

  
 
The purpose of this document is to provide the customer with some insight and trouble shooting tips with respect to servicing and/or repairing the DPF /DOC emission control after-treatment system on 2007 and newer on-road trucks. Please note: there are a variety of underlining engine issues that may need to be taken into account and considered over and above what is mentioned in this bulletin.
The DPF and/or catalyst will require servicing during normal engine operation, please refer to your OEM manual for recommended service intervals. The DPF and DOC can be serviced by an OEM or by an independent dealer that has the necessary cleaning equipment. There are cleaning and inspection guidelines that have been established by the DPF cleaning equipment manufacturer’s that provide information on determining whether or not a DPF is cleanable and still viable. It is recommended that a customer contacts only an accredited OEM and/or quality independent DPF cleaning facility in your area.
CLEAN-DPF-EXHAUST is just such a facility, and is the only one to offer a "CERTIFIED" clean DPF/DOC

The intent of this bulletin is also to highlight the importance of troubleshooting your DOC.
The DOC plays a vital role in keeping a DPF clean through on-board passive and active regeneration. When a DOC is no longer chemically active, or if it is beyond its useful life, the DPF will eventually become saturated with soot, which will result in total failure.


When to replace and/or trouble shoot the DOC


The catalyst/DOC will need to be replaced over time and especially if any of the following upstream engine issues have occurred (replacement is dependent on the extent and length of the failures.such as......
*EGR failure and/or coolant leak into the exhaust system*
*Turbo failures that lead to lube oil contamination into the exhaust system*
 *In-cylinder injector failure that causes poor engine operation and incomplete combustion*
When there has been an upstream engine issue such as those mentioned above, the engine will need to be repaired accordingly. However, depending on the extent of the failure, a DPF and/or DOC replacement may also be required.

 Please note: frequent active regeneration cycles may also be an indication that the DOC may be failing.

The constituents of coolant and engine oil are catalyst poisons. In low amounts the constituents are harmless to the catalyst, however as the amount increases, they become highly poisonous to the catalyst. If the DPF/DOC has been severely exposed to coolant or engine oil then irreversible damage has likely occurred and cleaning the DOC may not aide in salvaging and restoring the chemical activity of the catalyst. To determine whether the DOC is still chemically reactive, it is recommended to perform an active/forced DPF regeneration cycle at our facility.

Once a DPF and DOC have been serviced and all upstream engine issues have been repaired, a good preventative maintenance protocol is to test the after-treatment system during a forced/active regeneration cycle.
During an active regeneration cycle, raw diesel fuel is injected into the exhaust stream and is ignited by the DOC during proper operation. There are two temperature sensors located before and after the DOC, these sensors measure the temperature rise across the catalyst during active regeneration.
Temperature 1 (catalyst inlet) should be approximately 500-575°F and Temperature 2 (catalyst outlet) should be approximately 1000°F - 1125°F with an average differential temperature of ~500°F. On a properly functioning catalyst, the temperature rise across the catalyst will be ~ 500°F. Please note that other underlying issues can also result in low temperature readings such as a faulty temperature sensor, and/or insufficient diesel fuel injection, to name a few.
If the temperature rise across the catalyst is greater than 500°F, the chemical activity of the DOC is sufficient enough to ignite the diesel fuel during active regeneration. This does not mean that the catalyst has not been poisoned; however, it does confirm that the DOC still has chemical activity.
If the temperature rise across the catalyst falls below 500°F during active regeneration, this is an indication that the DOC may need to be replaced.

The DPF and DOC have become an integral part of the modern diesel engine, and proper DPF and DOC maintenance is necessary.
The DPF can fail for a variety of reasons; however the DOC is often overlooked as a plausible cause of DPF failure. It is important to understand that the DOC plays an important role in keeping the DPF clean during on-board engine operation. If a DPF is paired with a failed or inactive DOC, then recurring DPF plugging and excessive backpressure is inevitable. By measuring the temperature rise across the catalyst and monitoring active regeneration frequency, the operator can properly trouble shoot whether to replace the DOC, DPF or both.