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How to use the decoder to read the fault code?

Views:35     Author:Site Editor     Publish Time: 2020-09-16      Origin:Site

How to use the decoder to read the fault code?


The fault code is P1014

The flow rate in the  fuel pressure relief valve exceeds the threshold value during reverse driving; 


The fault code is P0504

The signals of the brake main and auxiliary switches are not credible; P2299: The throttle and brake signals are not credible.


According to the fault code, there are two faults related to the brake and accelerator. 

First, troubleshoot the fault. If you removed the brake switch and found that the contacts burned out a lot of black carbon powder, resulting in poor contact, so the computer version reported a brake-related failure after receiving the wrong brake signal. Replace the brake switch with a new one, and solve the fault code about the brake.


However, it is found that the speed limit problem will still occur. At this time, only the "P1014" fault code is left. Reverse drag means that the speed of the vehicle is higher than the engine speed. The vehicle is reversed and drags the engine to run, and the engine is in a passive drag State, this time does not need fuel injection to meet the needs of vehicle operation, so in this working condition, the fuel injector is not fuel injection. Generally, the failure point of "P1014" is the fuel injector, fuel pump, and metering unit. First, use a multimeter to measure the resistance between the two pins of the measuring unit, and the measured value is 2.9Ω (the Bosch measuring unit should normally be between 2.6 and 3.15Ω), and the resistance is normal.


Then use the shift fork to check the oil metering unit, there is no wear, jam, rust, etc.


Check whether there is a slight leakage at the high-pressure oil circuit connection pipeline, the appearance is normal, and there is no leakage.


After removing the test bench on the fuel injector, it was found after testing that the fuel return of three of the six fuel injectors exceeded the standard.

After replacing the fuel injector, test the car again, everything is normal and the fault is solved.


If there is no professional test bench, or the conditions do not allow, I will teach you a trick to determine whether the injector has high pressure leakage: measuring cup or measuring cylinder to measure the amount of fuel returned by the injector, and do not step on the idle speed. In the case of the throttle, the fuel return volume of each cylinder of the injector does not exceed 15ml (this is an empirical value and cannot be absolute. With the use of the injector, there will be wear on the valve seat of the needle valve. The oil return volume will become larger and slightly larger. If there is a high pressure leak and the valve seat is worn, the oil return volume will be large)


Use the decoder to read the fault code. The fault code is P01E8.

the rail pressure is lower than the first limit in the case of a small opening of the metering unit. Since the report is a failure of the metering unit, of course, check the metering unit first.


Check the fuel metering unit and wiring harness. Unplug the fuel metering unit wire, the measured resistance of A04 and A05 is 3 ohms; the key door is at NO, the voltage of A04 terminal is 25V, the voltage of A05 terminal is 3V; after the wiring harness is connected, the voltage of terminal A04 is measured as the wiring harness 25V, A05 terminal voltage is 24V. Through inspection, the voltage and resistance of the fuel metering unit are normal. And check the fuel metering unit, and found that there is no sticking, wear, etc.!


Since there is no problem with the fuel pressure relief valve, it should be a fault with low rail pressure. Therefore, a decoder is used to read the data stream of rail pressure. When the data stream shows a taxi, the actual rail pressure can only reach 170 bar, and the rail pressure is unstable, and the engine can only reach 200. Then there is no doubt that it is a fault with low rail pressure.


Apply direct current to the low-pressure oil circuit, disconnect the oil-water separator and diesel filter, use a transparent tube to direct both the inlet and return of the low-pressure oil circuit, start the engine, the engine still does not start. Check the fuel return volume of the fuel injector and the fuel return volume of the vehicle. The fuel return volume of the fuel injector is 0. The fuel return volume of the fuel pump is very large.


It is suspected that the overflow valve of the oil pump is damaged. Check the fuel injection pump. The oil pump has very little oil. The oil return of the oil pump is blocked and the engine can start. It is considered that the overflow valve is damaged. Replace the overflow valve and the problem is solved.


When the car is being repaired, although there is a fuel metering unit in the fault code, it actually refers to rail pressure. Although it is also necessary to check the metering unit, what is actually checked is the failure of rail pressure. You should directly check the data flow to see if there is a problem with the oil circuit. Therefore, we must analyze the fault code carefully, and consider it for ourselves to save a lot of effort.


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