Diesel Particulate Filter
The diesel particulate filter collects the soot and ash particles that are present in the exhaust gas of diesel engines. The diesel particulate filter assembly typically consists of active precious metals deposited on a substrate filter. The exhaust gas is forced to flow through the walls of the porous substrate and exit through the adjoining channels. The particulates that are larger than the pore size of the walls are trapped for regeneration. During regeneration the temperature in the diesel particulate filter increases to greater than 550°C (1,022°F). At this temperature the soot in the diesel particulate filter burns and becomes ash. The precious metal washcoat promotes the regeneration of the trapped particulates through the heat-generating reaction and catalyzes the untreated exhaust gas. The substrate filter is held in the metal shell by a ceramic fiber support system. The support system makes up the size differences that occur due to thermal expansion and maintains a uniform holding force on the substrate filter.
OPERATING CHARACTERISTICS
Diesel particulates in the exhaust are trapped by the DPF. Regeneration is the process by which exhaust temperatures are increased so the particulates are combusted.
The frequency and length of regeneration will fluctuate as both are determined by the drive cycle. For most drive conditions, regeneration frequency will vary from 100 - 600 miles (161 - 804 Km) between occurrence and last from 10 to 40 minutes. The first regeneration does not require 100 miles (161 Km) and may occur at any time. The length of regeneration is usually reduced if a constant speed above 30 MPH (48 Km/h) is maintained.
The following is a list of normal operation while the vehicle is in regeneration, and do not require repair. If you are not sure if the vehicle is in regeneration, IDS can be used to monitor the Diesel Particulate Filter (DPF) PID.
Engine idle speed can be 1100 to 1200 RPM in park/neutral with foot off brake.
High idle speed drops to within 50 RPM of normal idle when the brake pedal is touched, PRNDL is actuated, or clutch is actuated.
White smoke in cold ambients is normal and the amount will be increased during regeneration.
Powertrain power is limited to 325 horsepower (HP).
Engine responsiveness may be slightly different than normal operation.
During initiation of regeneration, exhaust smell may be noticed - especially on new vehicles.
Powertrain sound will be different including air induction noise (including flutter on deceleration or engine shut down), exhaust noise, and changes in engine radiated noise.
During regeneration, exhaust temperatures are elevated.
The Monitor
The powertrain control module (PCM) monitors the diesel particulate filter for leaks in the filter substrate. The diesel particulate filter requires preconditioning before the monitor is enabled. There are two tests that comprise the diesel particulate filter monitor. The first test is an efficiency
monitor that compares the restriction of the diesel particulate filter to restriction values, which are a function of exhaust flow. The second test is a differential pressure monitor that compares the measured differential pressure across the diesel particulate filter to threshold values, which are a function of exhaust flow.
The diesel particulate filter monitor is enabled and continuously runs after a preconditioning of 5,000 km (3,107 miles) when certain base engine conditions are first satisfied. The typical monitoring duration for this monitor is 2 minutes. Inputs from the crankshaft position (CKP), engine coolant temperature (ECT), exhaust gas temperature (EGT), and diesel particulate filter pressure sensors are required to enable the monitor. The monitor entry conditions include:
• diesel particulate filter regeneration is inactive
• one complete diesel particulate filter regeneration has occurred
• time from last diesel particulate filter regeneration is greater than 300 seconds
• exhaust flow between 400 - 2,000 m3/hour (14,125.9 - 70,629.3 ft3/hour)
• no fuel injector concerns
• preconditioning distance of 5,000 km (3,107 miles)
For the efficiency monitor test, the PCM determines a restriction threshold value for the amount of restriction that should be present in the filter for a certain exhaust flow rate. The PCM compares the measured restriction, which is based primarily on the diesel particulate filter pressure sensor measurement to the restriction threshold value. A fault filtering counter starts when the monitor begins to run. When the measured restriction is less than the restriction threshold, the counter increases. When the measured restriction is greater than the restriction threshold, the counter decreases. If the number of counts on the counter at the end of the monitor exceeds a calibrated
limit the diagnostic trouble code (DTC) P2002 is set and the malfunction indicator lamp (MIL) illuminates.
For the differential pressure monitor test, the PCM determines a differential pressure threshold for the amount of pressure that should be measured by the diesel particulate filter pressure sensor for a certain exhaust flow rate. The PCM compares the measured differential pressure value to the differential pressure threshold value. A fault filtering counter starts when the monitor begins to run.
When the measured differential pressure is less than the threshold value, the counter increases.When the measured differential pressure is greater than the threshold value, the counter decreases. If the number of counts on the counter at the end of the monitor exceeds a calibrated limit the DTC P244A is set and the MIL illuminates.