C0191 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 C0191 diagnostic trouble code may include:
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
Faulty or damaged wiring
Hesitation upon acceleration
If the DPF is not cleared the ECU will revert to the "Limp Home Mode" until the situation is corrected
Possible Causes :
A large air leak at or near the number one oxygen sensor would also cause a lean mixture.
Faulty IMRC actuator relay (if equipped)
Defective ECU strategies or components will prevent proper regeneration
Repair Processes :
Look for rubbing, scraping, bare wires, worn spots or melted plastic connectors. Pull the connectors apart and carefully look at the terminals (the metal parts) inside the connectors.
With the valve disconnected, the red voltmeter lead should be attached to the IMRC valve power wire and the black voltmeter lead connected to ground.
Diagnostic trouble code C0191 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 C0191.
Fortunately, C0191 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.