Failure phenomenon: a 2009 models new Bora sedan, equipped with a 1.6 L BWH-type engine, mileage 21000 km. The car suddenly stalled in motion, and then there’s the fault can not be started with this trailer dragged into the service station for repair.
FIG 1
Check Analysis: I take the car, first, the vehicle routine inspection, the inspection found: the starter can operate normally, but the engine without any sign of starting; VAS5052 diagnostic connector into the list of gateways for diagnosis, the engine control unit detects ldquo; can not achieve rdquo; failure, and other related control means also stores an engine control unit and a fault code can not communicate. The engine control unit ldquo gateway display list; not reach rdquo; (FIG. 1), indicating that the engine control unit can not establish communication with the gateway J533, the author determines engine can not start the initial failure is thus caused.
I found that the service check, when the ignition switch is opened, the EPC (Electronic Power Control) warning light on the instrument is no indication. Since the EPC warning lamp is controlled by an engine control unit, thereby further confirms this failure and an engine control unit associated. Any control unit to operate properly, the first condition is to have a stable operating voltage and good grounding, so I first check fuse engine control unit. Now that a circuit diagram of the fuse SC24 25 A (FIG. 2) providing 12 V power to the engine control unit and the ignition coil. After examination, SC24 unblown fuse, the fuse is not a 12 V power lamp test measurements found.
FIG. 2
Figure 3
According to the circuit diagram (FIG. 3), the fuse SC24 J317 relay powered by an instrument panel lower left. Here it is necessary to first understand how J317 relay. J317 is the relay power supply relay terminal 30, which is an engine control unit, the ignition coil, and some sensors provide the engine control system 30 is positively charged (constant power). This relay is a relay pin 5, No. 1 of the relay terminal loadSupply terminal, a second terminal to an output terminal number of the relay, the relay coil terminal 3 to the ground terminal, the terminal No. 4 of the ignition switch to the engine control unit 15 to provide positively charged, the fifth terminal of the relay coil 15 provided by an ignition switch is positively charged. When the ignition switch is turned on, the relay coil is energized to produce a magnetic field, so that contact sticking, relay terminal No. 1 and the No. 2 terminal is turned on, the two power supply through a fuse SC24 power terminals, thereby forming an ignition coil and an engine control unit 15 positively charged.
understood that the above-described circuit control principle, this fault diagnosis will have a basic idea, no fuse SC24 12 V power supply, it is necessary to check the power status of the relay 458. I turn the ignition switch, you can hear the sound of the closing of the relay, whereby the relay is working properly described. When taking into account the internal relay contacts of the fuse will lead to poor contact SC24 no power supply, so I disconnect relay J317, using a wire jumper its terminals 1 and 2, and then measure the supply situation fuse SC24, still no voltage is 12 V, thereby demonstrating no fault relay J317.
Now the circuit diagram and carefully I, also known as a relay J317 SC21, SC22, SC23, SC25, SC26 and SC27 several power fuse, a fuse and a relay SC24 connecting line only the power supply output No. 2 a branch. It was measured, each of the 12 V power inputs are fuse, thereby demonstrating the presence of open failure of the line connected to the fuse SC24.
Figure 4
I remove the instrument panel on the left side of the fuse box, a fuse SC24 relevant inspection line, no obvious visual inspection alone circuit phenomenon, then shaking central wiring harness assembly, issued hear J317 relay ldquo; tick rdquo; pull-sound, the EPC warning lamp on the instrument flickering.
At this time, to identify the real cause of the failure finally: open circuit fault in the wire harness branch center line. I follow it along the line, found fracture of the welded end of the wire harness, the wire harness peel found a copper wire has been broken into two cut (FIG. 4). What causes the wire to break it? The inspection found that the car fitted with remote control door locks, the author analyzes due to the maintenance personnel to install remote controlled gatesWhen movable lock breaking force welded end of this wire harness, resulting in breakage of the internal copper wire.
Troubleshooting: Since a central fault line branch wire bundle, thus causing the entire wiring harness assembly, in particular for large current carrying electrical lines are unsafe, so I replaced the central wire bundle assembly. After replacing the test, the EPC warning light, smooth engine start, the fault is corrected.
(Wangguang Hong)