After Jiefang Jh6 Changes The Urea Nozzle, The Fault Light Is Still On. What Should I Do

Today, we use this case to learn how to use the can network analysis function to quickly diagnose JH6 the vehicle LAN. The rational use of the diagnostic instrument can quickly lock the fault point, improve the maintenance efficiency and save time and cost.
A national five JH6 is equipped with tin diesel engine and independent board. During normal driving, the driver suddenly turns on the fault light, the accelerator is weak, and the vehicle is weak. The nitrogen and oxygen sensor and urea nozzle are replaced at the service station. The fault light is always on, and the fault code cannot be cleared.

Since the fault light is on, it means that the vehicle ECU has detected that there is a fault code in the electronic control system.
Regardless of any fault phenomenon, the fault code shall be handled first, and the fault code diagnosed by the diagnostic instrument JH6 (coachman C90).

Use multimeter and power test lamp to detect JH6

Next, use multimeter and power test lamp (large bulb test lamp) to detect JH6 the grounding / power supply line of nitrogen and oxygen sensor:
the resistance between the grounding wire and the frame is 0.3 Ω
the power supply voltage is 24V, and the brightness of the test lamp can be measured by the test lamp;
measure the can harness voltage: the can high / low voltage is about 2.5V, which is also normal;
Using the nitrogen and oxygen sensor test function, I found that the nitrogen and oxygen sensor is also good. That’s strange. The circuit is normal and the nitrogen and oxygen sensor is normal. What’s wrong?
It’s not difficult to understand why the problem has not been solved after many repairs.
Suddenly think of the can analysis function of the diagnostic instrument, and test it with a try attitude.
Let’s look at the picture and talk!

The scan node found that there is a nitrogen and oxygen sensor in the can network of JH6. Why can’t the engine ECU recognize the nitrogen and oxygen sensor? The problem can’t be found in the static state. Only the road test can be carried out.
The vehicle can scan the can network again after driving for five minutes. At this time, the problem comes, but the nitrogen and oxygen sensor is not scanned this time!!!

When the vehicle is still running, it is found that the power supply voltage is only 7.6v by detecting the nitrogen and oxygen sensor circuit again.

Are you ignorant? Still have ideas? Let’s learn the working principle of nitrogen and oxygen sensor, and then discuss why the detection voltage is abnormal after the road test of JH6.

The power supply is inactive, that is, the sensor has entered the preparation state. In this state, only pre heating is required. When the vehicle is driving, the exhaust temperature rises. After receiving the ECU signal, the sensor continues to heat to 800 ° C.
The JH6 current required at 800 ° C is much greater than the pre heating. The active state of the sensor JH6 continues to consume power, and the virtual connection of the line causes the sensor to fail to work normally. This is also why we can scan the nitrogen of JH6 and oxygen sensor in static scanning, The reason why you can’t find it during the road test. After the flight line test, the fault light goes out and the fault is eliminated

Summary of JH6

The diagnostic instrument has many functions. Only by being familiar with the functions of the diagnostic instrument can we solve the problem faster and more conveniently. Make rational use of the instrument to find the fault point. If you can use the diagnostic instrument, you will repair the diesel electronic control system. While tapping the potential of the diagnostic instrument, increase your personal business ability and earn more RMB! (text / truck house special author: coachman online)
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