P0120 is a kind of OBD-II Diagnostic P-Powertrain 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 P0120 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
Rich or lean exhaust
Possible Causes :
Faulty IMRC actuator relay (if equipped)
A large air leak at or near the number one oxygen sensor would also cause a lean mixture.
Defective ECU strategies or components will prevent proper regeneration
Repair Processes :
Now, clear the codes and test-drive the vehicle to see if the code is reset.
Look for missing ground strap or a rusty ground where the fuel tank is grounded to the frame. Check for damage to the wiring harness connector.
Diagnostic trouble code P0120 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 P0120.
Fortunately, P0120 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.