With the arrival of Euro 4, Euro 5, and Euro 6, the communication lines on the car have also changed. From the previous K, single set of can lines, to the current 2, 3, and even more than 4 sets of cans. . The increase in communication lines has brought great challenges and inconveniences to our car repair diagnosis. It takes a long time to check the pin map of the car information. Every day, we consult in the background on how to jumper the wire. The masters who find the pin map are countless. Today, the editor will give you an introduction, so you don’t have to worry about jumpers anymore!

First of all, let’s first understand what communication protocols the ECU has, why can’t it communicate, where is the diagnostic socket, and the computer board is abnormally powered?

一. OBD pin definition and communication protocol type

1. KWP2000 protocol: K-line communication

1. Judgment criteria: a signal line, the signal line voltage is generally 80% of the body voltage, about 1V lower than the body voltage, for example, the body voltage is 24, the signal line voltage is about 23V.
2. Application examples: Bosch system National III series; Delphi system; part of Denso system; Motorola system, etc.
3. Wiring method of diagnostic connector: power supply, ground wire, signal wire, please pay attention to the difference between signal and power supply.

2 Standard J1939 protocol: CAN.BUS communication

1. Judgment criteria: CAN.bus communication uses two lines: CAN-H high-end and CAN-L low-end.
CAN-H high end: voltage higher than 2.5V (usually 2.6V)
CAN-L low end: the voltage is lower than 2.5V (usually 2.4V)
Resistance: Turn off the key to measure the resistance between the signal lines (CAN_H and CAN_L) is 120 ohms, if there are other Can networks on the vehicle, it may be 60 ohms; please make sure that the signal line can communicate normally before testing.
2. Application examples: all Cummins series are CAN.BUS communication; Nanyue unit pump series are basically all; Yuchai Delphi unit pump series; some Japanese Denso systems, etc.

3. RS232 protocol: RS232 protocol communication

1. Judgment criteria: use two-wire communication
RS232-RD receiving terminal: The voltage of this line is between -9V and -5V. Note that the red test lead is connected to the signal line, and the black test lead is ironed.
RS232-TD transmitter: The line voltage is 0.1V, which is basically the same as the ground line voltage, so pay attention to the distinction from the ground line. The two lines are close together on the diagnostic socket.
2. Application example: Chengdu Wittur system full range (Note: Yuchai independently researched and developed Wittur unit pump system
Use CAN communication); Weichai OH1 natural gas system; some construction machinery vehicles use this kind of communication.

4. 485 protocol: J1708 protocol

1. Judgment criteria: use two-wire communication
J1708-A transmitting terminal: the line voltage is 4.8V
J1708-B receiving terminal: The voltage of this line is 0.1V, pay attention to the distinction from the ground line.
2. Application example: Weichai OH2 natural gas engine

5. K-line and L-line protocol: KL communication

1. Judgment criteria: K line voltage is about 4.8V, L line voltage is about 4.3.
2. Application example: Yuchai ECI natural gas series engine

二. The location of the diagnostic socket

1. Dongfeng Tianlong round 16-pin diagnostic socket is located in the fuse box on the right side of the center console
2. Dongfeng Cummins original power 3-pin diagnostic socket is located next to the ECU on the left side of the engine
3. Foton Auman standard OBD diagnostic seat is located behind the shift lever

4. Liuqi Balong round 16-pin diagnostic seat is located at the bottom left of the driver’s seat
5. Jiefang Sailong 3 round 16-pin diagnostic socket is located on the left of the steering wheel on the left side of the dashboard
6. Jiefang Sailong 2 round 16-pin diagnostic socket is located under the blower on the right side of the dashboard
7. Dongfeng Xiaobawang round 16-pin is located above the clutch pedal on the lower left side of the dashboard
8. Huatai Santa Fe standard trapezoidal 16-pin is located above the clutch pedal on the lower left side of the dashboard
9. Korean Ssangyong standard trapezoidal 16-pin is located above the clutch pedal on the lower left side of the dashboard
10. Great Wall Haval Standard Trapezoidal 16-pin is located above the clutch pedal on the lower left side of the dashboard
11. JMC Transit Standard trapezoidal 16-pin, above the clutch pedal at the bottom left of the steering wheel
12. A Volkswagen Bora standard trapezoidal 16-pin above the clutch pedal on the lower left side of the center console
13. Dongfeng Dolica round 16-pin on the panel on the lower left side of the steering wheel
14. Dongfeng Fashion/Super Dragon three plug small plugs have three positions
1>, is the lower left side of the steering wheel
2>, next to the ECU under the cover in the middle of the center console
3>, under the cover in front of the passenger seat
15. Shaolin box cargo Three small plugs under the cover in the middle of the center console
16. FAW New Dawei round plug on the lower right side of the steering wheel console
17. Yutong bus standard trapezoidal 16-pin inside the central distributor box behind the driver
18. Wuyue crane standard trapezoidal 16-pin inside the central power distribution box behind the co-pilot
19. XCMG crane standard trapezoidal 16-pin, lower left side of the steering wheel

20. Zoomlion Crane Standard Trapezoid 16-pin Inside the cover in front of the cab
21. SINOTRUK HOWO engineering vehicle standard trapezoidal 16-pin on the console on the left side of the steering wheel
22. Xiamen Golden Dragon China Bus Three-plug small plug, inside the cover in front of the co-pilot, next to the computer board
23. Foton Auman ETX round 16-pin (Yuchi 6J Bosch system) on the console on the lower right side of the steering wheel;
24. Dongfeng Tianjin:

1> Cummins/Aeolus Euro III, round 16-pin, on the upper right corner bracket inside the front cover of the co-pilot
2>, Cummins Euro IV standard OBD clutch pedal inside the left cover

25. Jiangling Classic Transit Standard OBD Central Relay Box in the small and medium lid,

三. ECU power on and jumper

To understand the OBD pin definition and communication protocol, we will take EDC17C55 as an example to interpret the ECU power-on and jumper:
1. EDC17C55 is powered on and controlled by the main relay. When the key switch is not moving (that is, the key switch is in the LOCK position), the red line indicates that there is a 12V voltage, of which the 12V voltage of line 50 is the slave relay 85 (86) Brought over
2. When the key switch is turned to the “ON” position, the T15 line is connected, and pin 71 receives the 12V voltage from the power supply, telling the computer version that I need to power on;
3. When the ECU detects that the No. 71 pin has a 12V voltage, it receives the power-on signal and will control the No. 50 pin to pull down the signal (equivalent to internal grounding), and the control circuit of the main relay is turned on;
4. After the control circuit of the main relay is turned on, the main relay is closed, the power supply circuit of the ECU is turned on, and the ECU is powered on.
It can be understood from the above that the 12V voltage of pin 71 is to lower the signal voltage of pin 50, and the voltage of pin 50 is to pull in the main relay to supply power to pins 4 and 6. Then I directly supply 12V to the 4th and 6th pins, and the 1st and 2nd pins are grounded. Will the ECU be powered on?
At this time, the ECU is not powered on, because the ECU not only detects the voltage of the 4th and 6th pins, but also detects whether the 71st pin has a 12V voltage (some models also detect whether the main relay is closed). If there is no 12V voltage on the 71st pin, even if the 4th and 6th pins are connected to the 12V voltage, the ECU will be dead.
If you want to power on the board separately, you need to connect 04/06 to the 12V power supply, and 01/02 to the negative power supply. Only connecting these two is not enough. You also need to connect the T15 line to a 12V power supply.
Through the above explanation, everyone should have a certain understanding of the ECU communication protocol and jumpers