I received an email from my dealer today regarding service for my '17 Volt. The maintenance it says it needs is "Check Engine, Electronics and Battery Pack Coolant and Check Sealant and Compressor Kit Expiration" Well....what in the world does 'Check Engine' entail? I can check the oil and battery pack coolant and I'm pretty sure all electronics work because, the car works! Do I need to do this service to stay under warranty??