The car engine P1816 Code is available in many car engines but meanings of the code are not similar. You must find out the real cause and meaning what you find in the car engine manual. The automobile dictionary meaning of the code let you know about the problem. The automobile dictionary meaning of the code is p for Powertrain Code Problem is related engine, transmission and emissions systems. 1 for MFG – Manufacturer Specific. 8 for Ignition System Or Misfire. 1 for Low Coolant Circuit. 6 for Cruise Control System – Vehicle Accel Too High. Do not use false meaning of the code for fixing the car engine.