Failure phenomenon: a 2005 annual SDL 1.5 L CVT car, mileage 92000 km. The car can not be started due to engine maintenance into the plant. Say users, the front part of the vehicle who suffered more serious collision, the car was also seen before vain phenomenon, but after a while will be able to place a normal start. There is also a strange phenomenon: when the car is easy to stall by bumps, but sometimes bumpy can return to normal, start the car.
Analysis Check: After I pick, first routine examination, found that the vehicle instrument display properly, sufficient battery power. Is connected to the vehicle fault diagnostic apparatus for testing, we did not find any fault codes. I try to start the vehicle and found the starter is operating normally, but the engine can not be started.
have a preliminary understanding of the phenomenon after the failure, I decided to check the vehicle’s fuel supply system is normal. I disconnect pipe joints at the fuel filter, the fuel gauge connection, and then turn the ignition switch and observe the fuel gauge readings showed normal oil; starter is rotated so that rotation of the ignition switch, and continue to observe the fuel pressure gauge , oil pressure is always within the standard range. At this point the fault rule out the possibility of the presence of the fuel supply system.
The author then check the ignition system is started, the car independent ignition system. I first removing plug checked, no abnormalities were spark plugs of each cylinder; further flashover test, the cylinders can not be found to produce high voltage arc described ignition system fault does exist. I found in the inspection, installation of the car alarm, then suspect a problem is caused thereby, so the anti-theft device is disconnected, the result is still not the ignition spark plugs of each cylinder, it precludes the possibility of malfunction alarm installation.
FIG 1
my analysis, no ignition of each cylinder a high pressure, the possibility of failure of the ignition coil 4, while a very small, but in order to Just in case, the author or the ignition coil for each cylinder line were examined. According to the circuit diagram (FIG. 1), a first cylinder plug 3P disconnect the ignition coil, the ignition switch is opened, the multimeter found: pin No. 3 BLK / WHT (black / white) line battery voltage; No. 2 pin BLK (black) resistance between the line and the ground is less than 1 Omega ;; No. 1 WHT (white) line, i.e., fromThe engine control unit a signal line, measured voltage is about 2.3 V. Above measurement results were normal. The author then in turn measured ignition coil 3P for the other three cylinders, the cylinder 1 with the measurement result is substantially the same. I Disconnect A plug engine control unit, measuring resistor 1 are signal lines between each cylinder and an ignition coil plug engine control unit, results were normal.
The results demonstrate the above measurement line 4 of the ignition coil is no problem, my analysis, when the engine control unit itself is faulty, the fault phenomenon will cause the car. In order to quickly find the point of failure, the replacement of an author to determine the available engine control unit, and matching the scan tool, and then try to start the engine, the results of the fault persists, the interruption is not caused by the engine control unit.
In this case a deadlock maintenance, I carefully analyze the diagnostic process, each of the ignition coil line is normal, the engine control unit is normal, the ignition coil 4 can not fail simultaneously, then what reason can cause no high voltage ignition it? After careful consideration, I believe that there is a possibility of failure of the ignition coil and the engine control unit can be ruled out, the focus should be concentrated on the inspection line between the ignition coil and an engine control unit. Each cylinder ignition coil ground line and the signal line is not suspicious, No. 3 Is the power line voltage is previously measured ldquo; virtual rdquo; voltage? In order to verify their own judgment, the author with a wire is connected directly across the battery terminals with the positive terminal 3 of each cylinder of the ignition coil, and then start the engine, the car engine is started smoothly, the vehicle returns to normal. This proves that the voltage of each cylinder of the power supply line 3 is indeed ldquo; virtual rdquo; voltage, i.e., the normal voltage but the current is very small, of the element does not work. This indicates the cylinder number associated with each of the power supply line 3 there is certainly a large line resistance.
using the method of step I decided to find the faulty measurement point, the measurement steps of: a circuit diagram, measuring the resistance between the battery and the positive electrode of each cylinder ignition coil connector terminal 3 is about 9.8 kOmega ;, confirmed Analyzing author; 1 measuring cylinder ignition coil plug number 3 24P plug terminal and the resistance between the terminals 5, the result is less than 1 Omega ;, normal; 24P resistance between the terminal and plug connector 2P No. 5 No. 1 terminal of the measurement is less than 1 Omega ;,Also normal; measuring the resistance between the fuse / relay fuse box (15A, fuse ignition coil) 2P plug 14 at the No. 1 terminal and the instrument panel about 9.8 kOmega ;, which indicates that the point of failure in the plug 1 from 2P No. terminal 14 to fuse this line. Disconnect connector 21P, 2P measure the resistance between the terminals of the plug 21P and the No. 1 terminal of the plug connector 18, then the result is less than 1 Omega ;, measured with No. 18 terminal 14 of the fuse socket connector 21P resistance between, the result is less than 1 Omega ;, were normal.
why the big resistance disappeared out? To find out why, I cut open the engine compartment fuse box began to check the wiring harness connector from the 2P at this line, found no local corrosion damage found problems along this line has been checked 21P connector: the connector 18 corroded terminals. To be sure this point 21P connector present at the contact resistance, resulting in the ignition coil 3, the power supply line voltage becomes ldquo; virtual rdquo; voltage, causing the vehicle can not start normally. Re-plugged connector 21P measuring the resistance between its terminals 18 and the plug 14 from the rear surface of the fuse, the results of a large resistance of about 9.8 kOmega ;, indeed appeared before described since this disconnect connector 21P segmented measurements, so there is no real measured contact resistance.
Troubleshooting: cleaning 21P connector terminals 18, fuse box replace engine compartment harness, failure to completely eliminate.
reviewed: ldquo; virtual rdquo; very subtle voltage, I began to have some oversight, resulting in a complicated whole diagnostic process. Thus, maintenance personnel in the power measuring line not to be trusted multimeter voltage reading, be sure to check the leads, in order to prevent ldquo; virtual rdquo; the voltage occurs. Further, when the conductivity measuring wire is also necessary to measure the resistance, because there is a large resistance when the wires are conductive. All in all, the case of conducting resistance wire is the most convincing arguments.
(red Wang, Zhang)