The Diesel Exhaust System and DPF Soot Accumulation

The diesel exhaust system on 2017-2018 Silverado and Sierra models and 2019-2020 Silverado 2500/3500 and Sierra 2500/3500 models equipped with the 6.6L Duramax diesel engine (RPO L5P) (Fig. 1) requires an occasional Diesel Particulate Filter (DPF) cleaning. Under normal driving conditions, the DPF cleaning occurs without any driving involvement. However, there may be circumstances that require a service regeneration to be performed.

Fig. 1

DPF Soot Level

Beginning with 2017 Silverado and Sierra models, the DPF Soot Accumulation is measured in percent instead of grams in GDS 2. The ECM will not try to perform a regeneration until the DPF Soot Accumulation increases to approximately 100%. If the DPF Soot Accumulation increases to 115% and the system has not been able to regenerate, the “Continue Driving” message will display on the Driver Information Center (DIC). If the DPF Soot Accumulation increases to 140%, DTC P2463 (DPF Soot Accumulation) will set and a service regeneration will be required to clean the DPF.

There are two soot level readings in GDS2. One uses the differential pressure sensor to calculate the soot in the DPF and the other uses other engine data. If either of these reaches the threshold, a regeneration will be performed.

 

Service Regeneration

A Service Regeneration is designed to lower the soot accumulation in the DPF in a very controlled way. It is not as effective at lowering the soot accumulated in the DPF as a Regeneration Enable followed by a drive.

Only perform a service regeneration if instructed in the appropriate Service Information. If there is a concern about the DPF Soot Accumulation, perform a regeneration enable and return the vehicle to the customer.

 

Vehicle Idling

Some vehicles may spend a lot of time idling. Use the following steps to aid in determining the equivalent mileage (kilometers):

  1. Record the total engine hours indicated on the DIC.
  2. Multiply the engine hours by 33 miles or 53 km. This represents an average speed of 33 MPH or 53 KM/H.
  3. The result should be close to or lower than the mileage on the odometer.

For example, if a vehicle has 1812.3 engine hours and 60,837 miles (97,908 km) on the odometer, the engine run time would equate to about 59,806 miles (96,052 km) (1812.3 X 33 = 59,806) (1812.3 X 53 = 96,052).

Since the calculated mileage is less than the actual mileage, the vehicle does not spend an excessive amount of time idling.

If the calculated mileage is more than the actual mileage, the vehicle would be considered a vehicle that idles a lot and this information may be useful in diagnosing any issues.

TIP: The engine hours formula should be used to aid in engine diagnosis only. It should not be used to determine any warranty claims.

 

How Regeneration Should Occur

The DPF traps the soot generated as a part of the normal operation of a diesel engine so that it is not sent into the environment. The process of regeneration enables the vehicle to clean the filter so it can trap more soot. Factors that determine when the ECM will try to perform a regeneration include:

    • After approximately 36 gallons (136 L) of fuel used since the last regeneration.
    • A maximum distance of 800 miles (1287 km) have been traveled since the last regeneration.
    • A pre-determined number of engine hours since the last regeneration.
    • A calculated or measured soot mass of 100% in the particulate filter.

When any of the above criteria are met, the ECM will perform a regeneration as soon as all the correct conditions are met. If the ECM cannot perform a regeneration, the ECM will only look at the soot mass to determine to display the Continue Driving DIC message or to set DTC P2463.

 

The ECM uses the following criteria to perform a regeneration:

    • Vehicle in Drive
    • BARO sensor 1 is more than 51 kPa (7.4 PSI)
    • Engine speed between 500 and 4000 RPM
    • Exhaust Gas Temperature Sensor 1 between 100 and 725 C
    • Exhaust Gas Temperature Sensor 2 between 95 and 750 C
    • Exhaust Gas Temperature Sensor 3 between 0 and 750 C
    • Exhaust Gas Temperature Sensor 4 between 60 and 750 C
    • Exhaust Gas Temperature Sensor 4 between 60 and 850 C
    • Engine Coolant Temperature between 50 and 140 C
    • Intake air temperature between -70 and 250 C
    • Fueling from -1 to 165mm3
    • Vehicle speed from -1 to 160 km/hr
    • No active DTC related to EGR, Indirect injector, or Throttle (boost)

The vehicle does not have a soot level sensor to determine how much soot is in the DPF. It uses algorithms to calculate the soot mass.

 

DTC P2463

When DTC P2463 sets, the ECM will no longer try to perform a driving regeneration and the vehicle will require the more controlled service regeneration. There are a number of factors that can cause the code to set, including:

    • The driver ignoring the Continue Driving messages
    • Leaks from intake or exhaust system
    • Poor fueling in the engine
    • Contaminated or bad fuel
    • Externally damaged or worn components.
    • Loose or improperly installed components
    • Dirty components (air filter or TMAP sensor)
    • Driving style, such as binary driving (frequently on/off accelerator or brake)

 

High Soot Levels

Factors that contribute to generating high levels of soot include:

    • Charge air cooler (CAC) and Air induction system leaks.
    • A restricted air filter.
    • Exhaust system leaks that may cause inaccurate Exhaust Gas Temperature sensor or Exhaust Pressure Differential sensor values.
    • Failed, intermittent, improperly installed, incorrectly wired or loose Exhaust Gas Temperature sensors may cause inaccuracies in the soot model. Look at all temperature sensors when the vehicle is cold to verify that they read close to each other.
    • Improperly routed differential pressure lines. The exhaust differential pressure line should have a continuous downward gradient without any sharp bends or kinks from the sensor to the DPF.
    • Leaks or internal restrictions from the Exhaust Pressure Differential sensor lines.
    • A skewed or shifted Exhaust Pressure Differential sensor will cause inaccuracies in the soot model.
    • A cracked or damaged MAF sensor housing.
    • A skewed, stuck in range, or slow responding MAF sensor. Inspect the MAF sensor for contamination.
    • Indirect Fuel Injector leaking or restricted.
    • Externally damaged or worn components.
    • Loose or improperly installed components.
    • Water in fuel contamination.
    • Engine mechanical condition, such as low compression.
    • Vehicle Modifications

 

Reducing the Number of DPF Regenerations

If a customer asks what can be done to reduce the number of DPF regenerations needed. Explain that when the “Continue Driving“ message is displayed (Fig. 2), the vehicle should be driven safely at a steady speed as close to the posted speed limit as possible, until the message turns off, which can take up to 30 minutes.

Fig. 2

In addition, driving with cruise control when possible will help the engine perform more efficiently as well as help the engine burn cleaner, resulting in less regenerations.

Driving at a steady pace without aggressive throttle application also will reduce the amount of soot generated by the system.

When descending an incline, use Tow/Haul mode to help with the ability of the vehicle to perform a regeneration.

The use of the diesel exhaust brake on declines will also help adjust the gearing to allow the vehicle to perform a regeneration. Keep in mind that on 2020 models, the diesel exhaust brake may not be as noticeable as in prior model year vehicles.

– Thanks to Larry Yaw and Rob Ritz

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