A yellow wrench light on a car's dashboard generally means that there is a problem with the vehicle's engine. The light is usually accompanied by a message telling the driver to take the car to a mechanic. There are a number of different things that could be wrong with the engine, so it's important to get it checked out as soon as possible. Depending on the severity of the problem, the car may be safe to drive, but it's always best to err on the side of caution and get it checked out.