C0312 is a kind of OBD-II Diagnostic C-Chassis Diagnostic Trouble Code.
It is considered generic because it applies to all makes and models of vehicles, although specific repair steps may be different depending on your car model.
Symptoms of a C0312 diagnostic trouble code may include:
Fuel pressure too high
Diminished fuel efficiency
Rich or lean exhaust
The engine oil will exhibit dilution from the ECUs attempts to increase engine temperature. Some vehicles advance the fuel injection timing slightly after top center to afterburn a small amount of fuel to increase exhaust temperatures. Some of this fuel enters the crankcase. When the ECU determines the necessity to regenerate the DPF, the service life of the oil be shortened significantly
Possible Causes :
A large vacuum leak would cause a massive amount of un-metered air to enter the intake manifold resulting in an overly lean mixture.
Faulty IMRC actuator/sensor
Faulty IMRC actuator relay (if equipped)
Repair Processes :
Once located, visually inspect the connectors and wiring. Look for rubbing, scraping, bare wires, worn spots or melted plastic connectors. Look for damage to the tank indicating impact that may have damaged the fuel pump or sender.
Diagnostic trouble code C0312 is not difficult to diagnose and repair. Thus, it always pays to have a qualified technician to look after your vehicle should this error code arise.
Diagnosing this code requires the engine to be in good running shape, without unmetered air entering the engine. If other codes that relates to misfiring condition, lean running or air entering the engine is present, then you must first fix those error codes before C0312.
Fortunately, C0312 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.