The exhaust particulate filter (EPF) captures diesel exhaust gas particulates, preventing their release into the atmosphere. This is accomplished by forcing particulate-laden exhaust (1) through a filter substrate of porous cells, which removes the particulates from the exhaust gas. The exhaust gas enters the filter, but because every other cell of the filter is capped at the opposite end, the exhaust particulates cannot exit the cell. Instead, the exhaust gas passes through the porous walls of the cell leaving the particulates trapped on the cell wall. The cleaned exhaust gas exits the filter through the adjacent cell. The EPF is capable of reducing more than 90 percent of particulate matter (PM).

The diesel oxidation catalyst (DOC) (3) has two functions. One function is to reduce emissions of non methane hydro-carbons (NMHC) and carbon monoxide (CO), from the exhaust gases. The other function is to help start a regeneration event by converting the fuel-rich exhaust gases to heat. The engine control module (ECM) monitors the functionally of the DOC by determining if the exhaust gas temperature (EGT) sensor 1 (6) reaches a predetermined temperature during a regeneration event. The DOC and the exhaust particulate filter (EPF) (4) are downstream of the turbocharger, and are two separate components bolted together under the vehicle.

The differential pressure sensor (DPS) (2) measures the pressure difference between the inlet and outlet of the exhaust particulate filter (EPF). When pressure difference has increased above a calibrated threshold, a high particulate loading condition is indicated. The ECM will command a regeneration event in order to restore the filter. If the pressure differential continues to increase across the exhaust filter without a regeneration event, the ECM will illuminate an EPF lamp or send a message to the driver information center (DIC) referring the customer to clean the exhaust filter. To clean the exhaust filter the vehicle must be driven under the conditions necessary for a regeneration to take place. If these lamps and messages are ignored, the ECM will eventually illuminate the malfunction indicator lamp (MIL) and revert to Reduced Engine Power which will require the vehicle to be serviced.

The DPS sensor provides a voltage signal to the ECM on a signal circuit relative to the pressure differential changes in the EPF. The ECM converts the signal voltage input to a pressure value.

The DPS pressure lines (5) are connected before and after the EPF. To provide the pressure sensor with accurate back pressure measurements, the DPS pressure lines should have a continuous downward gradient, without any sharp bends or kinks.

The ECM uses two exhaust gas temperature (EGT) sensors to measure the temperature of the exhaust gases at the inlet and outlet of the diesel oxidation catalyst (DOC). The EGT sensors are variable resistors, when the EGT sensors are cold, the sensor resistance is high, and as the temperature increases, the sensor resistance increases. When sensor resistance is low, the ECM detects a high voltage on the signal circuit. When sensor resistance is low, the ECM detects a lower voltage on the signal circuit. Proper EGTs at the inlet and outlet of the DOC are crucial for proper operation and for initiating the regeneration process. A temperature that is too high in the EPF will cause the DOC substrate to melt or crack. The ECM monitors the temperatures at the DOC inlet and outlet to regulate EPF temperatures.

The intake air (IA) flow valve is a throttle body assembly bolted to the intake manifold that is normally in the open position. The ECM commands the valve to close in order to precisely control combustion temperature control during exhaust particulate filter (EPF) regeneration. The IA flow valve will ensure the temperature of the exhaust gas remains in an efficient range under all operating conditions. The IA flow valve system uses a position sensor located within the valve assembly to monitor the position of the valve. The IA flow valve uses a motor to move the valve to a closed position and spring tension returns it to the open position. The motor is operated through Motor Control 1 and 2 circuits.

The exhaust brake is a throttle plate located in the exhaust system upstream of the diesel oxidation converter (DOC) and the exhaust particulate filter (EPF). The ECM commands the exhaust brake closed anytime during an EPF regeneration or engine warm-up event in addition to being used to reduce vehicle speed during a deceleration. The ECM commands the plate closed in order to precisely control combustion temperatures during EPF regeneration. The exhaust brake in conjunction with the IA flow valve will ensure the temperature of the exhaust gas remains in an efficient range under all operating conditions during the regeneration. The exhaust brake is controlled by a vacuum operated valve. The vacuum supplied to the valve is controlled by the exhaust brake solenoid, which in turn is controlled by the ECM. The operation of the exhaust brake is monitored electrically on the solenoid circuit as well as functionally by detecting mass airflow changes when the solenoid is commanded ON and OFF.

The exhaust system has been designed to reduce exhaust gas temperatures during regeneration. The exhaust cooler at the end of the tailpipe draws in cooler air as exhaust gases flow through its openings. The cooler air mixes with the warmer exhaust gas, reducing exhaust gas temperatures at the tailpipe outlet.

Regeneration is the process of removing the captured particulates through incineration within the exhaust particulate filer (EPF). Elevated temperatures are created in the diesel oxidation catalyst (DOC) through a calibrated strategy in the engine control system.

Regeneration occurs when the ECM calculates that the particulate level in the filter has reached a calibrated threshold using a number of different factors, including engine run time, distance traveled, fuel used since the last regeneration, and the exhaust differential pressure. In general, the vehicle will need to be operate continuously at speeds above 48 km/h (30 mph) for approximately 20-30 minutes for a full and effective regeneration to complete. During regeneration the exhaust gases reach temperatures above 427°C (800°F). If a regeneration event is interrupted for any reason, it will continue where it left off, including the next key cycle, when the conditions are met for regeneration. Normal regeneration is transparent to the customer.

Caution: Tailpipe outlet exhaust temperature will be greater than 300°C (572°F) during service regeneration. To help prevent personal injury or property damage from fire or burns, perform the following:

1. Do not connect any shop exhaust removal hoses to the vehicle's tailpipe.
2. Park the vehicle outdoors and keep people, other vehicles, and combustible material away during service regeneration.
3. Do not leave the vehicle unattended.

Caution: To avoid extremely elevated exhaust temperatures, inspect and remove any debris or mud build up at the exhaust cooler located at the tailpipe.

Notice:  Due to the elevated engine temperatures created while performing this procedure it is imperative to keep the front of vehicle in an open environment, with the hood open, away from any walls or buildings. This will ensure proper airflow across the radiator.

Important: Once the scan tool initiates service regeneration, the process cannot be stopped with the scan tool.

A scan tool is an essential tool that is required for this service regeneration. Commanding a service regeneration, normal or slow regeneration, is accomplished using the output control function. The vehicle will need to be parked outside the facility and away from nearby objects, such as other vehicles and buildings, due to the elevated exhaust gas temperature at the tail pipe during regeneration. The service regeneration can be terminated by applying the brake pedal, depressing the accelerator pedal or shifting out of Park or Neutral.

Using the EPF Regeneration Switch

A manual regeneration can also be accomplished by pressing the EPF regeneration switch.

The EPF regeneration switch only functions if the engine is running.

The EPF regeneration switch is a momentary ground input to the IPC. When the switch is depressed for 3 seconds, the IPC sends a message to the ECM requesting regeneration. The IPC also illuminates the LED in the switch by grounding the LED output control circuit. If a regeneration is not required at this time, the LED will turn OFF after 2-3 seconds. If a regeneration is needed at this time, thee LED will stay illuminated. A second activation of the switch under this condition will illuminate the yellow DPF light on the IPC and start regeneration.

A number of engine components are required to function together for the regeneration process to be performed. These components are the fuel injectors, turbocharger, IA flow valve, exhaust brake, and fuel pressure control.

The regeneration process consists of several stages:

Warming up the diesel oxidation catalyst (DOC) to 350°C (662°F) by performing the following:

Ash is a non-combustible by product from normal oil consumption. Low Ash content engine oil (CJ-4 API) is required for vehicles with the exhaust particulate filter (EPF) system. Ash accumulation in the EPF will eventually cause a restriction in particulate filter. Regeneration will not burn off the ash, only particulate matter is burned off. An ash loaded EPF will need to be removed from the vehicle and cleaned or replaced.