The trouble engine P0491 Code is very informative and if you have the right meaning of the code, you can solve the car engine properly. The engine code is found in the car engine and the same engine is found in many car engines what you need to study. The right meaning of the code is easy to find according to the brand of the car. is P for OBD-II Diagnostic Powertrain (P) Trouble Code For Engine. 0 for Intake Valve Control Solenoid Circuit Low. 4 for Engine Oil Temperature Sensor Malfunction. 9 for Cylinder 10 Contribution/balance Fault and 1 for Reverse Input Circuit.