With the continuous strengthening of social awareness of environmental protection and the increasingly strict national laws and regulations, the new update speed of today’s vehicle models and post-treatment systems is also faster and faster, and the way of experience maintenance is more and more difficult to adapt to the development of the industry. This paper introduces a maintenance case of Bosch 6.5 urea pump that cannot be repaired according to previous experience of urea pump.
Model: JAC Junling h330
Configuration information: equipped with Bosch edc17c81 Bosch 6.5 urea pump
Fault phenomenon: no urea burning, engine torque limit
Fault code: see the figure below of urea pump
The current fault affecting urea burning is p20a0, which belongs to the fault related to urea pump circuit during the self inspection of SCR system. Before the self inspection, the SCR system stops working and reports a fault. Engine torque limit activated and 4th fault reported of urea pump.
1. According to Bosch 6.5 urea pump pin definition, measure the power supply and PWM signal voltage of urea pump harness 5 and 6-pin reflux pump. There is no voltage at the pin. It is suspected that there is a problem with the harness.
2. However, an abnormal phenomenon was found during the measurement, and there was no power supply to the pump motor. Open and close the key door once, and then measure the 12V voltage, but then the voltage disappears.
According to our maintenance experience, the power supply of the urea pump is in a long-term state after the ECU is powered on. Why is there sometimes no power supply for the pump of this car. After checking the circuit diagram, it is found that Bosch edc17c81 is different from our frequently repaired edc17cv44 in the harness part of the pump.
It can be seen from the figure that after the ECU relay is pulled in, the SCR main relay is controlled to pull in, and the pump motor and reflux pump are powered.
Turn on the key ECU to monitor whether the power supply is normal through the PWM control end of the pump. After completing the self-test, the SCR main relay is disconnected. It is normal to measure the power supply of pump motor first and then whether it is available. However, the power supply of the reflux pump has not been, and it is judged that it is a circuit fault.
3. Test the function with the actuator, keep the SCR main relay closed, measure that the power supply of the pump motor is normal, and measure that the power supply of the return pump is not.
4. Quickly verify the fault point, cut the original vehicle harness and directly fly the wire to the power supply end of the reflux pump. When the self-test is completed, the fault code p20a0 becomes a historical fault.
5. After the driver completes three driving cycles, the SCR system works normally and the torque limit is released.
It can be seen from this case that the power supply of the urea pump is usually in the long-term power state after the ECU is powered on, and the power supply of the SCR system of this vehicle is controlled by the ECU by monitoring whether the power supply at the PWM control end of the pump is normal. Therefore, according to the previous maintenance experience, it may take a detour. It also needs a strong foundation of the circuit and professional diagnostic equipment to be invincible.
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