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The Post-Treatment Does Not Burn Urea, So It Is Easy To Solve The Problem, Okay

Bosch 2.2 post treatment system, urea pump, urea pipe and urea tank need heating. At present, the commonly used schemes are electric heating of urea pump and urea pipe and cooling water heating of urea tank of burn urea.

Case Sharing Of Burn Urea

One Jiefang J6 is equipped with Bosch 2.2 post-processing system, the fault light is on, and the read fault code is as follows of burn urea.:

All faults are post-treatment heating faults, and they are open circuit faults. The troubleshooting steps are as follows:

Unplug each relay, measure the harness voltage of control line pins 85 and 86, one 24V and one 3.5V are normal; Measure one 24V and one 0V of the controlled pins of the main relay, and the other 87 and 30 pins of the relay are 0V, and the voltage is normal.

Check and replace the heating relay, and the fault remains;

Measure the resistance of urea pipeline, and the resistance between pins 5 and 6 (heating) of urea pump is normal;

Check that the urea pump connector and each connector connector are normal.

Finally, it was found that the negative grounding fuse of post-treatment heating had poor contact. After repair, replace the fuse, and the system was normal of burn urea..

Heating Logic

We know that the standard urea solution will freeze at – 11 ℃, and the volume will increase by about 7% after freezing. In order to prevent the parts from cracking due to freezing, it is necessary to pump the urea back into the urea tank after shutdown; In winter, the temperature in the northern region is very low, – 11 ° C is an easy temperature to reach. The SCR system cannot work normally when it is frozen, so it needs to heat the ice.

Water heating is also used for urea pumps of some systems. For example, Hino engine adopts water heating urea pumps. We focus on the electric heating system of burn urea..

Urea Tank Heating

The urea tank is heated by water, and the coolant solenoid valve controls whether the engine coolant flows for heating. When the temperature sensor in the urea tank detects that the temperature is lower than a certain limit, start heating. When the temperature is higher than a certain limit, stop heating. Generally, when the temperature is lower than 0 ℃, ECU opens the solenoid valve to heat the urea solution to 5 ℃, and closes the solenoid valve (different items) of burn urea.

The resistance of coolant solenoid valve is generally about tens of ohms to 100 ohms, and the resistance of common coolant solenoid valve is about 40 ohms.

In addition, when replacing the coolant solenoid valve, pay attention to:

The model of coolant solenoid valve must be selected correctly. It is basically normally closed and cannot be mistakenly selected as normally open. Mistakenly selecting normally open will cause excessive heating of urea and some chain reactions.

When installing the coolant solenoid valve, there is a direction. There is an arrow on it. Do not install it upside down.

Urea Tank Heatingurea Pipe Heating

The urea pipe is electrically heated. The urea pipe is wrapped with resistance wire, which generates heat when powered on, just like the household electric blanket. Judge whether heating is required according to the ambient temperature and control it through the heating relay. The resistance generally ranges from tens of ohms to hundreds of ohms of burn urea.

Urea Pump Heating

The urea pump is electrically heated, and there is a heating resistance wire inside the pump, which is covered on the filter and flat plate. 2.2 pins 5 and 6 of urea pump are heating pins. The resistance of 24V system is about 6 ohms, and that of 12V system is about 1.5 ohms. Generally, judge whether heating is needed according to the temperature in the pump (temperature signal is transmitted through the speed control line of the pump motor), and control it through the relay of burn urea.

In order to prevent overheating, there are two protective resistors on the heating circuit of the pump. When the temperature is higher than 110 ℃, the resistance becomes infinite of burn urea.

Heating Circuit

To understand heating related faults, first understand the heating circuit diagram. The following figure is the schematic diagram of the heating circuit. The post-treatment heating circuit has five relays in total, one main relay, and the live wire controlling the heating of urea pipe and urea pump of burn urea.

Four auxiliary relays, namely pressure pipe heating relay, return pipe heating relay, inlet pipe heating relay and urea pump heating relay, control the corresponding pipeline and the negative pole of urea pump heating. Simply understand that the main relay controls the heating live wire and the auxiliary relay controls the grounding of burn urea.

The following figure shows the post-treatment heating relay of Jiefang J6, which is located on the left side of the passenger’s safety box in the cab. Compare it with the above figure of burn urea.

The working principle of the relay will not be repeated. Just remember one sentence: the condition for the pull-in of the relay is that there is a voltage difference between the two control lines. Simply put, the relay is pulled in when there are two pins 85 and 86, one is 24V and the other is 0V of burn urea.

So How Does Ecu Control Pipeline Heating?

The main relay has two control pins, one connected to K90 and the other connected to K94. K90 is the 24V power output from the ECU. When K94 outputs a low battery, a voltage difference is formed at both ends, the relay is pulled in, and the heating end of the pressure tube is powered;
When the pressure tube needs to be heated, K92 outputs a low battery, a voltage difference is formed between the two control pins of the pressure tube heating relay, the relay is pulled in, and the heating end of the pressure tube is grounded;
The heating end of the pressure pipe has 24V power, one end is grounded and connected, and the heating resistance wire is heated.
You may have questions. What is the feedback line K58 for? Imagine that if the ground wire is broken, the tube heating cannot be carried out normally, but the ECU does not know. This wire is used as an “informant” to tell the ECU whether there is a problem with the harness, relay and heating pipe. If there is a problem, the ECU reports a fault and lights up the fault light.
Knowing the principle of the above fault, the troubleshooting is very simple. Now review the fault case just now, and you can understand why the open circuit fault is reported!
In the future, if you encounter heating faults, it is recommended to check them from simple to complex. Give priority to checking all relays and fuses, then check the resistance of each heating element, and finally check the line. Step by step, you can always solve the problem.