Diesel Aftertreatment Validation
DIESEL AFTERTREATMENT VALIDATION - 6.7L
Aftertreatment System:
OVERVIEW
When trying to understand the functionality of the exhaust and aftertreatment system, (more precisely the effects on the Diesel Particulate Filter DPF)) you must think in terms of standard plumbing principals. Everything flows downstream. Systems and components along the path are affected by the soot in the exhaust, and these components can also contribute to the soot levels (cause and effect).
This overview will attempt to elaborate on the causes and effects of the Soot flowing downstream in the system. The soot originates in the combustion chamber as by-product of the combustion process. This is the beginning of the stream. All soot generated in the combustion chamber flows downstream. Excessive amounts of soot can be caused by faulty inputs to the engine controller, air handling system leaks or restrictions, fuel contamination, or fuel injectors. Some soot will always be generated. Under proper operating conditions, soot levels will be low and very manageable.
The next component downstream is the EGR. The EGR can be affected by soot coming from the combustion process. The soot can cause the EGR to stick open or closed, or become restricted. If the EGR malfunctions, it can cause soot generation which is then added to system.
The next component downstream is the Turbocharger. The Turbocharger can be affected by soot coming from the combustion process and/or the EGR. If the Turbocharger malfunctions (sticks, or leaks oil or coolant internally), it can cause soot generation which is then added to system.
The next components found downstream are the O2 sensors. The O2 sensors can be affected by soot coming from the combustion process, the EGR, and/or the Turbocharger. If an O2 sensor malfunctions, it can cause (to a much lesser extent) soot generation which is added to system. O2 sensor codes can be caused by excessive soot.
ALL of the soot generated upstream will land in the DPF. If a vehicle sets a DPF DTC, such as P1451 or P242F, which are related to the calculated amount of soot currently caught in the DPF this means the engine controller has calculated that the DPF is getting full. This number is and estimation, hence the name, "Estimated Soot Load Based on Delta" (ESL/D) and is measured in grams. Sometimes soot levels will be estimated high and set faults and there is little soot in the DPF.
When a DPF fault sets, it is important to root cause the reason the soot landed in the filter and could not be removed through a normal regeneration. Is fuel contamination the issue causing injectors to stick and over fuel? Is the EGR or Turbocharger sticking causing excess soot? Or is it a combination of these?
A DPF should NEVER be replaced without first determining if there is another root cause of the source of the high "Estimated Soot Load Based on Delta" and repairing this issue also. A DPF should also not be replaced without performing the Aftertreatment Inspection Guideline procedure. This will visually show you with examples how to determine if replacement of an aftertreatment component is necessary.
1. HIGH PRESSURE FUEL SYSTEM TEST
1. Before starting the validation, confirm on the scan tool that the engine is still at an operating temperature of 180F (82C).
2. Using the scan tool, navigate to System Tests and perform the High Pressure Fuel System diagnostic procedure.
NOTE: The High Pressure Fuel System test is a comprehensive fuel system test that operates the engine and fuel system under several diagnostic operating conditions. When the test is complete, the engine will stall. In MOST cases, this test can determine IF there are any fuel system issues, and if so, whether diagnostics should begin at the LOW pressure side or the HIGH pressure side of the system. Based on the results of the test routine, you will be directed to either start testing at the low pressure side (step 5) of the system or go directly into the high pressure side of the system in order to shortcut the diagnostic time. However, if the test routine fails and you are directed to the high pressure side of the system and do not find an issue at the completion of the test, it is recommended that you go back to test step 5 and continue with the rest of the fuel system testing. This test routine should also be used to validate that the system is operating properly after the fuel system has been diagnosed and repairs are completed.
Did the High Pressure Fuel System Test PASS?
Yes
- Record the results into step 9 of section 4D "After Treatment Validation Test"
- Go To 2
No
- Vehicle is NOT repaired. Perform the CHECKING THE FUEL DELIVERY SYSTEM test procedure to diagnose and repair the vehicle. Component Tests and General Diagnostics
2. FUEL SYSTEM RUN UP TEST
1. Before starting the validation, confirm on the scan tool that the engine is still at an operating temperature of 180F (82C).
2. Using the scan tool, navigate to System Tests and perform the Fuel System Run Up diagnostic procedure.
NOTE: This test will take approximately 270 seconds to complete. The ECM will cut out each individual Fuel injector three times and calculate the delta RPM change. Based on the delta RPM change, the test will indicate a bad cylinder based on the limits that have been set. When the test is complete, the engine will return to idle. This test routine should also be used to validate that the system is operating properly after the repairs are completed.
Do the results indicate that a cylinder is out of spec?
Yes
- Vehicle is NOT repaired. Perform the CHECKING ENGINE MISFIRE/RUNS ROUGH/PERFORMANCE test procedure and continue troubleshooting the faulty cylinder condition starting at test step 9.
No
- Record the results into step 10 of section 4D "After Treatment Validation Test"