Case 1
Failure phenomenon: a 2005 annual Beijing Hyundai Sonata sedan 2.0 L, users often repair the engine radiator fan switch.
Check Analysis: First, verification failure phenomenon, as long as the ignition switch is turned to the low speed often turn radiator fan, engine start switch is also often low. Found radiator fan to provide a control circuit diagram of the original, you can see the fan harness connector is shown a circuit diagram of the line 4, and line 2 is the actual vehicle. Found yilante fan control circuit diagram (FIG. 1), the control principle and the plug was found the number of lines agree with the actual vehicle, but the position of the stitch lines do not match the color of the actual vehicle.
FIG 1
car radiator fan control procedure is as follows: a current B + rarr; rarr radiator fan relay; radiator fan motor, another way radiator fan relay separated rarr; high-speed condenser fan control relay, the condenser fan motor in series and then to ground the low speed circuit configuration. Symptom is now radiator fan motor and condenser fan motor with a low speed, possible points of failure includes a radiator fan relay is damaged, the radiator fan relay control circuit has a problem (in series to ground), damage to the coolant temperature sensor line .
FIG. 2
measured, and found no radiator fan relay control circuit in question, relays are not damaged. See data stream coolant temperature value and the temperature values shown in the same table. Find maintenance staff temporarily lost direction, much deliberation, will be the engine control unit controls the fan speed rotation of it? See fault diagnostic use GIT engine system stream, and found the engine control unit receives a signal of the air conditioner switch (FIG. 2), and the control of the radiator fan relay, resulting in a low speed rotation of the fan after the ignition switch is opened. See air conditioner switch is not pressed, the air conditioner switch suspected engine control unit to the line problems. See a circuit diagram of the air conditioning system (FIG. 3), the air conditioner switch can be seen alignments, air conditioner switch JM09 through C11 to pin A11 of the foot JC02 then the engine control unit. First find JM09 the C11, exit plug pins, turn the ignition switchAfter low-speed rotation or off radiator fan, air conditioner switch and status display data stream is still ON, the air conditioner switch described thus far there is no problem JM09 line. Then exit A11 plug pin JC02, the ignition switch is turned found fan does not turn, and the air-conditioner switch signal indicates OFF, then the locking point of failure is the engine compartment relay box internal short circuit, causing erroneous air conditioning switch signal to the engine control unit, whereupon the engine The control unit controls the fan speed rotation.
Figure 3
Solution: Replace the engine compartment relay box, test troubleshooting.
reviewed: at the start of maintenance, maintenance personnel think the problem is simple, the fan works poorly thought, there is no data stream full use of the engine, resulting in repair work a few detours.
Case 2
Failure phenomenon: a 2009 annual China FRV 1.6 L sedan, say users, after the vehicle is started, open the instrument when the turn signal is not sent ldquo; tick rdquo; Tips sound.
Check Analysis: First, verification failure phenomenon, found the case of opening an ignition switch (not starting the engine), the turn signal when the instrument has opened ldquo; tick, tick rdquo; tone, after starting to open as long as the steering light, there is no beep, the engine tachometer and stopped at bit 0 does not move, do not move during acceleration, the fuel gauge bit 0 also stops.
Based on the above symptoms, the author analyzes the failure like a power meter (30) power is lost or instrument failure. In order to accurately determine the fault, with reference to a circuit diagram of the instrument are often the ignition switch power supply to check the power supply voltage is normal, without disconnection or short circuit, grounding the meter check is normal. Then replace the instrument, the results are disappointing, the fault does not change anything. See again the circuit diagram, seen from the circuit diagram of the steering signal to the steering switch rarr; BCMrarr; bulbs steering instrument, after the start, turn signals the external work, so I suspect by the BCM output signal line branching out to the meter signal line may there is a problem, but why the instrument of a turn signal is also normal, but no beep? With questions I remove the instrument, turn the steeringLight meter to check the signal line, a signal may be supplied normally.
While tachometer failure did not respond, but the power to ground are normal. Users at this time and reflects the vehicle accelerates bad, I feel bad, like spark plugs, so I replaced the spark plugs.
troubleshooting: After replacing the spark plug, all faults have disappeared vehicles.
Review Summary: For the entire repair process, while checking the line has found no problems, replace the component can not solve the problem, you should consider the source of interference caused by signal distortion on whether the vehicle. The main reason is the idea of technicians rather narrow, not enough for a comprehensive analysis of the problem. After the spark plug is damaged, breakdown resistance becomes larger, resulting in an increase in the primary current of the ignition coil, the field coil becomes strong, produced over shield limits interference of the vehicle, causing the vehicle breakdown phenomenon occurs more.
(Li Xin)