The front left tire of my car got a sidewall cut as shown in the picture (I am not sure when and how long ago it happened). I have already read this article (Can this tire sidewall damage be repaired or should I replace the tire?). But I am still not sure in my situation, should I replace the tire? If yes, should I replace all four tire or only the damaged tire? The car is a Honda CR-V 2014 AWD model, the millage is about 33,000. If yes and I do not replace the tire, what would happen? Just got a flat tire or tire will blast on the road? Thanks.
As @David said, absolutely, change the tire immediately. In view of the age of the tires, unless they were spectacular tires to begin with, they are probably all due for replacement. If you do not feel this is necessary, at least replace the other tire on the same axle.
The risk with a tire that is this damaged is that it will burst a huge hole while you are driving, unlike a normal car puncture which is small enough and slow enough that you have time to deal with it. Am I saying this will kill you? Possibly. A blown tire can send your car out of control and... fill in the blanks. Furthermore, even you succeed in bringing the car to a controlled stop, who knows where you will be stranded for how long.
Better replace it now, since you know the damage is there. Save lives; drive responsibly.
Yes, replace the tire immediately. I'd recommend replacing both tires on that axle, but not all four unless they are as bald as that one appears to be.
Despite what tire shops will tell you, it isn't necessary to replace all four tires at a time. However, if you have one old / low tread tire and one new tire paired up (both fronts or both rears) you can get slippage between the sides which will wear at the older tire even faster, and can cause traction and ride quality problems.
On a front-wheel drive car, I could see it accelerating transaxle wear, but that's just my instinct and not something I've researched.
While you're at it, make sure there aren't any similar cracks or tears in the other tires.
While I agree this is a deep cut, and I do not like seeing the structure of a tire from the outside, keep in mind this is on the sidewall. Ask a tire shop for their advice, I wouldn't be surprised if they tell you to use rubber glue and press the cut back together. The cut has smooth edges.
A cut like this on the rolling surface is an other story altogether. Cuts on sidewalls are usually more forgiving, although this one does look very deep. Go to a tire shop and have them look at it. If you need to replace the tire, then like everybody else, change the 2 on that axle if your other 2 tires are still in good shape.