A Zhongtong LCK6125 bus was equipped with a Weichai WP10.360 diesel engine. The throttle failed during driving, the idle speed was increased to 1100r/min, and it entered the Limphome state.
When the idling speed is 1100r/min, most of the faults are caused by the electronic throttle or the throttle circuit. Connect the diagnostic instrument to read the fault code. The current fault is that the voltage of the accelerator pedal 1 is higher than the upper threshold. Because the car is 12 meters long, the wiring harness of the throttle position sensor is also more than ten meters, and the wiring harness is fixed in the frame, which is difficult to find. So first measure the resistance characteristic of the throttle position sensor and it is within the normal range. To ensure accuracy, connect the throttle position sensor to a vehicle of the same model and work normally, remove the sensor failure.
Disconnect the original wiring harness of the throttle position sensor from the connector, and reconnect the wires to test according to the ECU wiring diagram, that is, make a new wiring harness connecting the throttle position sensor and the diesel engine. After the new connection, everything is normal, so that it can be concluded that the original car’s throttle position sensor harness has malfunctioned. The next step is to find the faulty part of the wiring harness.
Diesel engine wiring harnesses are generally bundled and bundled together, and they are not prone to failure unless they are affected by external forces, such as pulling, squeezing, friction, and baking, which cause the insulation to crack or the wire to break. Although a “flying wire” method can be used to reconnect the line fault, if the faulty part is not found, the external force of the faulty part will always act on the fault point of the harness, causing more line faults. If you encounter conditions such as water ingress, it may cause a short circuit and burn the entire vehicle circuit or ECU computer.
When checking the line of the car to the diesel engine, it was found that a wiring harness was attached to the exhaust pipe of the diesel engine, and the corrugated pipe was damaged. When the corrugated pipe was peeled off, two wires were found to be damaged, as shown in Figure 2. One of them is the throttle signal line. After the line is connected, the fault is resolved.
At present, the domestic electronically controlled common rail diesel engine mainly adopts the second-generation common rail system. Its technology has been quite mature after more than ten years of development abroad, so the failure rate of the system itself is very low. As domestic diesel is not up to standard, it has caused the failure of the high pressure common rail system oil circuit and injector; the layout of the body line is mainly the responsibility of the OEM, so it is also a high-prone component; the throttle position sensor is generally purchased by the OEM. , Not included in the system, its failure rate is much higher than that of the diesel engine’s own sensor