XCOM 2
87 Achievements
GOG
Car Wrecked
Cause an enemy to die in a vehicle explosion
49.9%
How to unlock the Car Wrecked achievement in XCOM 2 - Definitive Guide
From my experience it takes 2 normal grenades to make a vehicle blow up.
When an enemy is taking cover behind a vehicle use a grenade/launcher. The result will be the vehicle starting to catch fire. Now use your second grenade to destroy the vehicle.
If an enemy has full health you may need to weaken it so that the car explosion can do enough damage to get the kill. In this case simply position your first explosive so that it covers both the enemy and the car.
When an enemy is taking cover behind a vehicle use a grenade/launcher. The result will be the vehicle starting to catch fire. Now use your second grenade to destroy the vehicle.
If an enemy has full health you may need to weaken it so that the car explosion can do enough damage to get the kill. In this case simply position your first explosive so that it covers both the enemy and the car.
Throw grenades at an enemy near a vehicle so they take some damage and the vehicle lights on fire, but don't kill them with the grenades. Then throw grenades so they hit the vehicle without hitting the enemy so that its the vehicle's explosion that kills them.