Understanding the control logic of ECU and the correct use of detection equipment are very helpful for rapid maintenance. The following case is a car failure caused by a small fault. Let’s understand the control logic of ECU on the starting system of J6.
Model: FAW Jiefang J6
Engine: Xichai ca6dl2-35e3
Emission: Guosan
Computer board: Bosch edc7uc31
Fault phenomenon: the headlight doesn’t light up and the heater doesn’t turn. After inspection, it is a white main line. The power line is broken and normal after repair; The starter doesn’t work in a taxi. It is suspected that the line repaired just now broke the starting line of J6.
Troubleshooting steps:
1. Use a test lamp to measure that there is no power at the control end of the starting relay.
Fault analysis: according to the circuit diagram, when the starter is not working, there is no working voltage at the control terminal. When it needs to work, ECU controls the high-end output of 24V, and the high / low-end forms a voltage difference to pull in the relay. When starting the test, there are three possibilities that the test light does not light up of J6.
1) Yes, the starting conditions are not met, and the ECU does not output the high-end control.
2) The harness at the control end of the start relay is faulty.
3) ECU is damaged.
The vehicle starts normally when it comes, and the ECU damage may be very small. Give priority to checking the harness fault at the control end.
2. Check the harness. The harness is normal without short circuit and open circuit.
3. Check the neutral switch and forcibly start the key for ten seconds without response. Connect neutral switch signal line 1.85 and public high-end 1.04 together, and there is still no response when starting.
4. Check T50 signal and disconnect ECU plug 1. Use the test lamp to measure No. 1.61, start the test, there is power, and T50 signal is normal of J6.
5. Connect the two wires 1.37 and 1.51 at the control end of the starting relay to the starting relay. Connect the relay control end to the test lamp to start the test, and the test lamp is on.
6. Connect the start relay and there is no response at the start. The fault point is confirmed in the starting relay, and the fault is eliminated after replacing the relay of J6.
Fault summary: why is there power at the end of the computer board and no power at the end of the relay?
Check that the control end of the relay is short circuited to the tower iron state. When ECU controls the operation of actuator, it will conduct self inspection on the status of actuator. When the line at the control end fails, a fault code will be reported, and the actuator will no longer be controlled. It is suggested that when the starting relay fails to supply power, the masters should first open the relay circuit and use the test lamp instead to detect the circuit of J6.
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