a 2009 annual Chery Cowin 1.5 L sedan, equipped with SQR477 engine, 5 500 km mileage. Users can not reflect the car engine flameout fault often, but every time maintenance personnel rushed to the scene when a failure occurs without, so maintenance staff has not seen a failure. Users say when a fault occurs even when the key is removed, the engine is still running and the vehicle can travel, but simply open the engine hatch or door switch, sometimes the engine will stall. Failure does not occur again within a period of time.
In general, the cause of the engine mdash only one still can not switch off the ignition flameout; mdash; 30 (B +) and the constant power supply 15 (IGN) power for short circuits. If the door switch or the case bonnet reflect true user, indicating that the resulting vibration of the short-circuit point is disconnected, the engine will naturally died.
as is the occasional failure, the author arrived at the scene after the vehicle but also the normal starting and stalling repeatedly test about half an hour, the fault has not appeared. Connection failure diagnostic system for testing the engine control, did not find any fault codes, only this time based on past experience with specific characteristics of the vehicle and an engine control system according to troubleshoot exclusion. The door is opened when the bonnet switch or failure of the user to reflect that the engine stall will, I believe that should be analyzed virtual access lines, it is suspected engine control unit, the presence of the main fuel pump relay and relay virtual connection and, therefore, they re-plug the 1. While I will be ready when the engine hatch shut checked once again, there has been a failure in the car after the ignition key is removed, the engine does still continue running smoothly. It also found that the relevant fault and the dashboard warning light indicators are on. If the power supply 30 and power supply 15 is shorted, the parking brake lamp on the instrument panel and the seat belt indicator remains lit. But now the relevant lights are off, indicating no short circuit between the power supply 30 and power supply 15. This situation makes failure more complex.
after
FIG 1
I decided to open the engine compartment cover inspection engine control system associated circuitry, but pulled a bonnet, failure vanished.After another failure no longer occurs, the operation appears to open the engine hatch is a breakthrough. So I carefully recalled operation when just open the engine hatch, but I was operating relatively light, how would suddenly change failure phenomenon? Thus the use of flashlight engine hatch pull handle carefully observed, as found in the engine compartment cover pull wire knob moves back and forth to change position, thereby opening the engine compartment cover. Outside the engine hatch cable sheath, so it feels not to interfere with any thing. Later, I also carefully observed around the engine hatch pull handle, found on the engine hatch pull handle above the meter harness grounding outlet has a connector (Figure 1) there is loosening, is it due to loose this Ground Line . To verify judgment, I decided to disconnect the connector and observe the reaction of the engine. When I disconnect the connector, and then closed again to start the engine, then the engine really surprisingly found not stall. When the grounding wire-bound back, the engine can stall the normal test. Trial several times, could not confirm the cause of the engine flameout of the connector is loose.
FIG. 2
Figure 3
is the ultimate cause of failure was unexpected car . After checking the correlation circuit diagram (FIG. 2) field measurements and field, the author determines that the vehicle body connector antitheft control unit (FIG. 3) of the main line to ground. Vehicle anti-theft control unit is a relatively simple one kind of anti-theft vehicle body, mainly to control a normally closed relay switch controlling the ignition power supply 15 feet off security features implemented by the antitheft control unit. When the ignition switch is turned in the armed state, the control unit controls the anti-theft relay is normally closed, normally closed relay case (FIG. 4) by a pin No. 30,87a state is turned ON pin numbers 30,87, and 87 feet foot air, the engine can not because there is no power ON start. When the engine is started, the current state defenseless condition is affirmative, then the control unit does not control the anti-theft relay is normally closed, the normally closed relay pin No. 30,87a is normally conducting state. While the ignition switch is ON, the regular power source 30 via the ignition switch in three simultaneous to 5 feet 86,30 and normally closed relay antitheft control unit, the vehicle must often other power closed relay output pin No. 87a. When the antitheft control unit good grounding, security controlPin No. 5 manufactured by means of the ignition switch is turned off after 0.04 mV; Remove the grounding line, off after the ignition switch approximately 2 V. But as long as the engine is started again after switching off the ignition, the control unit 5 feet immobilizer actually about 4 V to a voltage signal.
Figure 4
In sum the measurement result, because I believe that the presence of the antitheft control unit grounding line phenomenon virtual connection, the internal circuit can not be formed antitheft control unit, cause its foot high potential appears at No. 5. At this time, the high potential of about 4 V is present across the power line, the engine control unit receives the naturally voltage signal. To be noted, two power car engine control unit 30 provided by the regular power source, while the fuel pump relay, fuel injectors, ignition coils and the oxygen sensor heater element associated electric power supply by the main relay. Main relay by the engine control unit, engine control unit 13, the car ignition pin power supply as a position signal only, role is an ignition switch to the engine control unit. While the antitheft control unit does not cause the engine 4 V voltage signal generated by the control circuit unit recognizes the presence of the signal, it is determined that the ignition switch is still erroneous ON position, the engine can not stall. When the user opens the door switch and the engine cover, so that due to vibration and then a solid grounding line, the engine stall can be naturally. In fact, when the vehicle can not turn off, the remote controller can not be used, but because the user can not turn off the engine, naturally no longer use the remote lock, so that the fault most obvious feature is hidden. Depending on the circumstances of the car, the author should be determined that a failure related art flooring gum accidentally pull the harness decoration in the user, resulting in the virtual connection connector.
Finally, after the failure test connector insertion place excluded.
(Qin Zhigang)