Required if you are replacing a water pump on an Ecotec engine. DO NOT buy a sub tool, you will drop a bolt in the timing chain and regret it. Removing the timing cover is a pain. If you drop a bolt it can go all the way into the oil pan. If it hits the oil pan, you won't be able to reach it with a scope with a magnet attached. If it falls into the oil pan, it must not fall to the bottom of the pan. The frying pan has two tiers. I know that from experience.