The automobile dictionary meaning of this car engine P2688 Code is found online for free and you can use this meaning of the code for solving the car engine. The car engine code lets you know the real problem and location of the car engine when you know the actual meaning of the car engine code. The general meaning of the code is p for Powertrain Code Problem is related engine, transmission and emissions systems. 2 for MFG – Manufacturer Specific. 6 for Vehicle Speed Control And Idle Control System. 8 for Exhaust Gas Recirculation System Valve 1 and 8 for PCM Stack Overrun.