Hybrid powertrains rely on liquid coolant to remove heat from the electric motors, batteries and inverters, which are often hidden behind the rear seats, under the floor or in the trunk area, and rely on carefully managed airflow combined with special coolant and radiators. I remember a Honda Insight that lost this coolant due to a rock striking the grille area, setting a check engine light on the dash. The owner ignored the warning and kept driving the car, until forced to stop on the side of the road. That tiny pebble caused the hybrid power system to overheat and take out some other components - several thousand dollars in repairs. Hybrid batteries use the car’s engine to turn an alternator or an electric motor to charge them, maintaining a complex balance of power to provide brisk acceleration or electric-only driving, then burning fuel to recharge the battery bank and extend driving range. These cars and trucks are designed to be driven, and they do great when used in a daily commute and as taxis and delivery vehicles, but they aren’t so happy when you only make short trips or leave the car unused for long periods. We’re seeing a few more of these cars coming to us for diagnosis of starting and drivability problems.