B0939 Diagnostic Trouble Code

B0939 is a kind of OBD-II Diagnostic B-Body 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 B0939 diagnostic trouble code may include:

Faulty or damaged wiring
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
Poor fuel economy
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.
A large vacuum leak would cause a massive amount of un-metered air to enter the intake manifold resulting in an overly lean mixture.

Repair Processes :

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 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. Oxygen sensors signal the engine management computer the amount of oxygen present in the exhaust, which is used in determining and controlling the fuel ratio.

Process Tips

Diagnostic trouble code B0939 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 B0939.

Fortunately, B0939 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

B0939 Trouble Code For Specific Cars

B0939 Toyota Lexcen Oil Temperature Sensor Circuit Failure
B0939 Lancia Dilambda Speed Wheel Sensor LR Input Short Circuit To Ground
B0939 Alfa Romeo 179 ABS Power Relay Output Open Circuit
B0939 Geely Bo O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 3)
B0939 Nissan Gt-r Clutch Position Sensor Circuit Range/Performance Malfunction
B0939 Bianchi S Brake Pedal Input Circuit Ground Short
B0939 Buick 2235 Cylinder 3 Contribution/Balance Fault