U0139 is a kind of OBD-II Diagnostic U-Network 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 U0139 diagnostic trouble code may include:
Cherry red hot catalytic converter
The light may stay on or light intermittently as the DPF regenerates. The engine will be sluggish on acceleration.
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 :
Defective ECU strategies or components will prevent proper regeneration
The Mass Airflow sensor is a hot wire that senses the volume of air entering the intake manifold. The computer uses this information to control fuel mixture.
An air leak forward of the DPF will change the sensor readings resulting in the code
Repair Processes :
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.
If you find a related TSB, the information will often help in diagnosing the code in question as TSBs are crested from many thousands of repairs.
Look at the plug wires to make sure they are not burnt or laying on the exhaust.
Diagnostic trouble code U0139 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 U0139.
Fortunately, U0139 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.