The after treatment system is a set of components designed to work in conjunction with a engine that is working properly.
 

This means if the engine has any issues, smoking, skipping, low power, or drive ability, it will cause after treatment issues.

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Eighty percent of regeneration issues are due to a failure on behalf of the engine.

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The Diesel Oxidation Catalyst (DOC) creates the heat needed doing the regeneration, it contains ceramic material with other precious metal coatings which reacts to diesel fuel when introduced into the DOC by the dosing valve. The DOC is a pass through filter. If there is a upstream issue that produces a lot of soot, it will cover up the precious metals and the DOC will no longer produce the heat needed for the regeneration process.

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Every vehicle has a targeted temperature in which it starts to introduce diesel into the DOC. If the vehicle does not reach its targeted temperature (The temperature needed to began the dosing process) you should check for a issue on the engine side.

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If the exhaust system never reaches the temperature to begin the dosing process, check for codes in the engine, check for turbo VGT actuator issues, command vs actual, EGR command vs actual, intake throttle, command vs actual and check for exhaust leaks.

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When there is no issues with the vehicle's engine or exhaust system the vehicle will always perform regenerations when needed. A forced regeneration is mainly for the purpose of diagnosing. A forced regeneration allows the tech to be able to see if the vehicle is able to reach the targeted temperature, and to check the after treatment injector efficiency, to check to see if the DOC is efficient.

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With the key on and engine off, the differential pressure should be near 0, the voltage to the differential switch should be less than 1 volt. When the vehicle is started, the voltage should go up slightly. Hold the throttle open and you should see the voltage increase rapidly if the DPF is restricted. If it is not restricted, you should see little change in voltage signal to the differential sensor. (2 to 3 volts).

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If you find that the filter is restricted, run a regeneration and recheck the voltage to the differential sensor. If you see a voltage drop of 1 volt or more then the regeneration was helpful. You should see a pressure drop at the pressure sensor also. (It should drop to about half of what it started out at).

If while doing a regeneration, the DPF outlet temperature exceeds the DOC outlet / DPF inlet temperature and remains that ways for the duration of the regeneration, the DOC is plugged, or has lost its precious metals. If it is plugged, it will need to be cleaned.

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Snap acceleration test: This test allows for you to see if there is an upstream issue with the vehicle. To perform this test, first disconnect the exhaust from the front of the DOC, accelerate the engine about four to five times, holding the accelerator down for two to three seconds at a time. If you see a lite puff of smoke that clears up, that is normal. If the smoke does not clear up, there is a upstream issue, failed injectors, intake throttle valve, worn pistons / rings, turbo, exhaust brakes, EGR, coolant assumption, over filled engine oil, etc. These issues will quickly plug your DPF.

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Checking your temperature sensors: With the key on, engine off, the temperature reading on all of the sensors should be within 20 degrees of atmospheric temperature. (Plus or minus)

 

These are just a few quick tests that can help you to troubleshoot the after treatment system. When it comes to the after treatment system, it is our goal to help you to keep your vehicle running trouble free.

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