The automobile dictionary meaning of the car engine P1390 Code is p for Powertrain Code Problem is related engine, transmission and emissions systems. 1 for MFG – Manufacturer Specific. 3 for IC Module 4X Ref Circuit Intermittent, No Pulses. 9 for Crankshaft Position Sensor Circuit Performance. 0 for Transmission Engaged At High Throttle Angle. The engine P1390 code seems a kind of powertrain problem. While fuel economy was enlarged, acceleration was extremely negotiated, and the loss of engine vacuum led to a seriously unsafe loss of braking support when the engine P1390 code system was in four-cylinder mode. Fix the car engine following proper meaning of the car engine code.