C0121 Diagnostic Trouble Code

C0121 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

Symptoms of a C0121 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
The light may stay on or light intermittently as the DPF regenerates. The engine will be sluggish on acceleration.

Possible Causes :

An air leak forward of the DPF will change the sensor readings resulting in the code
Rusty exhaust systems, cracked exhaust manifolds or damaged or missing gaskets or donuts will cause air leaks.
Defective ECU strategies or components will prevent proper regeneration

Repair Processes :

It should be pretty close to battery voltage (12 volts). If not, then this is the circuit that has the problem. 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. Look at the plug wires to make sure they are not burnt or laying on the exhaust.

Process Tips

Diagnostic trouble code C0121 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 C0121.

Fortunately, C0121 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

C0121 Trouble Code For Specific Cars

C0121 Mazda Miata Turbocharger Boost Sensor B Circuit High
C0121 Lexus Gs TCM Power Input Signal Range/Performance
C0121 Suzuki Sx4 Mirror Driver Switch Assembly Circuit Open
C0121 Porsche Cayenne Fuel Pulse In Range But Lower Than Expected
C0121 Willys-overland Whippet SCP (J1850) Invalid or Missing Data for Seat Motion / Control
C0121 Hyundai Hcd
C0121 Gaz 32 O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)