The DPF system has been applied in the fifth stage of China, but there must be some masters who know a little about it! Since July 1, 2019, the national six emission standard has been implemented in key areas, and DPF has been basically applied to every vehicle. If you don’t know DPF, you can’t make a little money.
Train of thought determination: in case of insufficient power during maintenance, the first step is to read the fault code. If the fault indicated by the fault code does lead to insufficient power, troubleshoot according to the fault code. If there is no fault code, it can only be analyzed through data flow.
01: read data stream
Use the diagnostic expert to read the fault code and display two current faults:
P2463: particle trap (DPF) adsorbed particle overload
P2463: the particle mass deviation (measured value analog value) of particle trap (DPF) exceeds the upper limit of level 2 monitoring
The fault code literally means that there are too many particles adsorbed by the DPF. In essence, the signal voltage fed back to the ECU by the differential pressure sensor is high. The possible reasons are the following aspects. We mainly consider these aspects when troubleshooting.
① Circuit problems
② DPF blocked
③ Differential pressure sensor failure
④ ECU fault (very few)
When the first fault is reported, the warning light will be turned on, and the ECU will call the torque limit function to limit the engine. I’m afraid this is the reason why the car has insufficient power. Now that the reason has been found, don’t talk more nonsense and start to solve the fault code.
Look up the circuit diagram and find that the open circuit voltage of the differential pressure sensor is 5V, 5V, 0V. Unplug the plug of the differential pressure sensor, measure the open circuit voltage with a multimeter to supply 5.74v, signal 5V and ground 0V. The voltage is normal. It is preliminarily judged that there is no problem with the circuit.
As there is just a new differential pressure sensor, replace the old differential pressure sensor directly. After power on, read the fault code and display the current fault, which proves that the fault has nothing to do with the differential pressure sensor.
Not familiar with DPF failure? The old driver told you how to repair it
Tip: since there are new parts of the differential pressure sensor during the troubleshooting, the replacement test is directly carried out, and the accuracy of the replacement test is higher than that of measuring the skin breaking voltage. Here is the standard value of the signal voltage of the differential pressure sensor at several speeds (broken skin), which is convenient for the masters without replacement test conditions.
Note:
① The above table shows the data of edc17c81, which may vary from project to project.
② Generally, the differential pressure sensor does not need to measure the resistance to judge whether it is good or bad. It can be tested directly by replacing parts or check the appearance.
05: DPF regeneration
Note:
① The above table shows the data of edc17c81, which may vary from project to project.
② Generally, the differential pressure sensor does not need to measure the resistance to judge whether it is good or bad. It can be tested directly by replacing parts or check the appearance.
Tip: DPF is divided into passive regeneration and active regeneration
① Passive regeneration has been continuously carried out. However, due to the influence of driving environment, slow speed, low DPF temperature, slow oxidation speed of carbon particles and low efficiency, DPF blockage is easy to occur. At this time, it needs to be solved by active regeneration.
② There are two types of active regeneration. The first is that the ECU controls the automatic regeneration during vehicle driving, that is, driving regeneration. The second is the active regeneration by manual operation when the vehicle is stationary, which is called in-situ regeneration or one click regeneration.
After DPF regeneration, an important step is missing, that is, DPF reset. DPF reset is to clear the carbon load of the system and let the ECU know that the DPF is not blocked.
After resetting the DPF, read the fault code again, the current fault becomes a historical fault, and the refueling door can be added.After the DPF was reset, the fault did not appear again for a period of time, and the fault was solved.
01: p2463 fault code is reported. Why is torque limited?
DPF is a particle trap, which usually cooperates with EGR exhaust gas recirculation device. If DPF related faults are reported, ECU thinks that the PM capture capacity of DPF is reduced or invalid. For exhaust emission related faults, the most common strategy is torque limiting. At the same time, DPF fault code will also lead to the shutdown of EGR system. A torque limiting curve of Bosch p1671v310 is selected below to explain how to limit torque.
Not familiar with DPF failure? The old driver told you how to repair it
The x-axis in the figure above shows the speed, from 1500rpm to 2700rpm. Z axis is torque, and each speed corresponds to a current torque limit. When p2463 fault code is reported, ECU calls this curve to limit the engine. For example, when the speed is 1500 rpm, the torque is limited to 300 n · M.
Tip: after some fault codes causing torque limit are reported, ECU will call the corresponding torque limit curve to limit the engine
02: what are the trigger conditions for DPF regeneration?
DPF regeneration generally has three trigger conditions, namely:
① Mileage trigger, generally regeneration once every 1000km
② DPF differential pressure sensor signal triggers regeneration
③ Carbon load triggered regeneration
Not familiar with DPF failure? The old driver told you how to repair it
As shown in the figure above:
① When the carbon load is less than 18, the DPF system adopts passive regeneration. At this time, the engine operates normally, and no relevant warning light is on in the instrument.
② When the carbon load is between 18 ~ 30, it is active regeneration. The engine operates normally, but the exhaust temperature is high, and the high exhaust temperature lamp is on.
Not familiar with DPF failure? The old driver told you how to repair it
③ When the carbon load is between 30 ~ 40, the driver shall be used for manual regeneration.
④ When the carbon load is between 40 ~ 45, the system will report the fault code related to DPF blockage, the engine is severely limited, the engine fault light is on, and the in-situ regeneration must be carried out immediately.
⑤ When the carbon load is greater than 45, the shutdown indicator is on. At this time, it is necessary to manually handle the DPF, remove the DPF, blow it out with an air gun or replace it with a new DPF.
Tips: ① water washing is not recommended for DPF. The coating may be washed off, resulting in DPF failure! It is recommended to clean with air gun or special tools, or replace them.
Not familiar with DPF failure? The old driver told you how to repair it
② After replacing the DPF, reset the DPF and let the ECU recognize that it is a new DPF.
03: definition and calculation of DPF
① Differential pressure: differential pressure is the pressure difference between the front and rear ends of DPF, also known as pressure drop, which is related to airspeed and exhaust temperature.
Where is pressure drop, DPF upstream pressure and DPF downstream pressure. When it exceeds a certain value, the fault of DPF blockage is reported, and it should be handled at this time. When it is close to 0, it is reported that the DPF is removed, which may be due to air leakage in the exhaust pipe at the front end of the DPF or burning through of the DPF.
The following figure shows the differential pressure sensor. It should be noted that the connector with larger inner diameter is connected to the upstream of DPF and the connector with smaller inner diameter is connected to the downstream of DPF. The pressure pipe should not be installed reversely.
Not familiar with DPF failure? The old driver told you how to repair it
As shown in the figure below, the relationship between DPF pressure difference and exhaust temperature is shown. X-axis is exhaust temperature and y-axis is pressure difference. It can be seen from the curve that when the exhaust flow is constant, the greater the exhaust temperature is, the greater the pressure difference is.
Not familiar with DPF failure? The old driver told you how to repair it
Correspondingly, as shown in the figure below, the relationship between DPF pressure difference and exhaust flow is shown. X-axis is exhaust flow and y-axis is pressure difference. It can be seen from the curve that when the exhaust temperature is constant, the greater the exhaust flow is, the greater the pressure difference is.
Not familiar with DPF failure? The old driver told you how to repair it
② Capture efficiency of PM particles: the capture efficiency of DPF particles can generally reach 80% ~ 95%, so DPF will have greater blocking risk than POC.
Not familiar with DPF failure? The old driver told you how to repair it
Not familiar with DPF failure? The old driver told you how to repair it
③ DPF carbon load: the ratio of particulate matter captured by DPF to carrier volume is the carbon load of DPF.
Not familiar with DPF failure? The old driver told you how to repair it
Not familiar with DPF failure? The old driver told you how to repair it
The maximum allowable carbon load of DPF carrier under various restrictions is called the maximum allowable carbon load required (m-sml).
04 why does the speed increase during regeneration?
Because DPF regeneration needs to have exhaust temperature conditions, in order to improve the exhaust temperature, the fuel injector carries out post injection and the ECU controls to increase the speed, which is generally increased by 1000-2500 R / min for about half an hour. When it returns to the idle state, it proves that the regeneration is completed.
Supplement: in the sixth national phase, the increase of DPF front-end temperature is divided into two stages;
Phase I: raise the temperature of DOC front end; When active regeneration is required, the temperature sensor detects the front-end temperature of doc. When the temperature is less than 350-400 ℃, the engine improves the exhaust temperature to about 350 ℃ through in cylinder measures (intake valve and adjustment of injection advance angle) to fully activate the conversion efficiency of doc.
Not familiar with DPF failure? The old driver told you how to repair it
The second stage: increase the exhaust gas temperature at the front end of DPF; When the exhaust temperature is detected to be higher than 350-400 ℃, the DPM system injects fuel upstream of doc. The injected fuel is fully mixed with the tail gas in the tail pipe to form a fully uniform distribution state. The mixed fuel is burned in the doc tail to heat the tail gas temperature to about 600 ℃, and the particles captured by DPF are burned and eliminated at high temperature.
