Call of Juarez: The Cartel
51 Achievements
17-21h
Chain reaction
Kill at least 20 enemies by exploding nearby vehicles.
37.3%
How to unlock the Chain reaction achievement in Call of Juarez: The Cartel - Definitive Guide
There are also sections where reinforcements roll up in a car. Shoot it until it is on fire, wait for them to get out (I waited for the doors to close after they got out) then blow it up for 2-4 easy kills.
An excellent spot for 6-8 kills instantly is on the last level when chasing Alvarez, he runs through a small garage with a few cars and a bunch of guys. Blowing up one car almost always causes a chain reaction with the others and wipes out almost everyone in the room.
The earliest this can be unlocked is in Chapter 2. Please note that NOT all cars can explode in the campaign. When you are inside the house with all the ammo and defending your position from the waves of enemies you must shoot the cars near the enemies. A second place in that chapter is a little later during the gun fight in the parking lot with all the vehicles. Do not kill any of the enemies by shooting them directly but just shoot the vehicles and make them explode. If done correctly you will get a blue icon on the bottom right corner of the screen showing “Chain reaction x/20”, which will tell you of your progress.
Shooting an enemy vehicle will cause it to explode and consequently will kill any nearby enemies. There are many sections in the game that this can be obtained. The first good spot to grind if desired, would be on Chapter 2 after exiting the house and making your way back to the parking lot where you started the level. When entering this area, there will be a good amount of enemies near cars, making this an ideal location. If desired reload checkpoint and repeat.
Simply, during the chase, shoot at cars with enemies inside.
5-6 cars and the achievement will open.