There are thousands of roads, safety first. If the exhaust gas does not meet the standard, the driver takes out his wallet. With the continuous development of society, everyone’s awareness of environmental protection is gradually strengthened. With the frequent introduction of environmental protection policies and the national focus on environmental protection, diesel vehicles, as a major polluter, are the focus of motor vehicle emission control. When there are problems with vehicles, they must be repaired in time. The next step is to bring you post-processing related cases!
Model: Foton GTL
Engine: Cummins isge4-400
Post processing: Cummins Ecofit
Fault phenomenon: the instrument fault light is on and the engine power drops. The owner also found that the urea solution is not consumed since the fault light is on.
Fault analysis:
We read two fault codes through the decoder (handyman C80):
4239 aftertreatment 1 SCR injection air auxiliary absolute pressure – data valid but above normal operating range – moderately severe.
4177 aftertreatment 1 SCR injection air auxiliary valve – voltage below normal or short circuit to low voltage power supply.
Check that the definitions of the two fault codes all point to the post-processing air solenoid valve. The literal meaning of the fault code “4239” is understood as that the air pressure is effective but exceeds the maximum upper limit. Most of this problem is the failure of the pressure stabilization of the air solenoid valve. The fault code “4177” air auxiliary valve voltage is lower than the normal value or short circuit to low-voltage power supply is a historical fault, which will not be handled temporarily.
1. Through the previous analysis, give priority to the current fault code “4239”, and use the decoder to perform the override test (post-processing injection test or test with the lathe maker B80 urea pump test bench). During the test, it is found that the pressure of the mixing chamber reaches about 700KPA, significantly exceeding the maximum upper limit of spraying urea.
2. Replace the air solenoid valve and clean the urea pipeline. Then continue to use the detector to perform the override test. The pressure of the mixing chamber returns to normal 362kpa. Repeat the test for three times and the pressure of the mixing chamber has been in the normal range of spraying urea.
3. Use the decoder to clear the fault, and there is one historical fault that cannot be cleared: “4177 air auxiliary valve voltage is lower than normal value or short circuit to low-voltage power supply”. Although it is a historical fault, it will affect the post-processing system. Next, measure the open circuit voltage of the air solenoid valve to be 24V and 0V respectively. After measuring, check the circuit diagram (online query by the lathe maker) and find that the open circuit voltage of the normal control line should be about 12V of spraying urea.
4. Check the harness from the control end of the air solenoid valve to K13. In order to quickly diagnose the fault, find the harness of K13 pin from the ECM plug and cut it. It is found that the ECM outputs 12V voltage at both ends, but the other end is connected with the body iron. The fault point is confirmed. The control harness of the air solenoid valve is short circuited with the negative pole. Directly from the K13 flying wire of the computer board to the control end of the post-treatment air solenoid valve for troubleshooting.
When diagnosing faults, we should have clear troubleshooting ideas and understand the working principle of components.
For example, the working principle of Cummins Ecofit post-processing:
Under normal conditions, the metering pump has the following four working stages: initialization – pre injection stage (pressure building after emptying) – metering stage (pre injection and injection) – emptying stage.
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