P1939 Diagnostic Trouble Code

P1939 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

Symptoms of a P1939 diagnostic trouble code may include:

Faulty PCM
The light may stay on or light intermittently as the DPF regenerates. The engine will be sluggish on acceleration.
Poor acceleration
Diminished fuel efficiency

Possible Causes :

Faulty IMRC actuator/sensor
A large vacuum leak would cause a massive amount of un-metered air to enter the intake manifold resulting in an overly lean mixture.
A large air leak at or near the number one oxygen sensor would also cause a lean mixture.

Repair Processes :

It should be pretty close to battery voltage (12 volts). If not, then this is the circuit that has the problem. Look for damage to the tank indicating impact that may have damaged the fuel pump or sender.

Process Tips

Diagnostic trouble code P1939 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 P1939.

Fortunately, P1939 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

P1939 Trouble Code For Specific Cars

P1939 Maserati Ghibli Transmission Fluid Pressure Sensor/Switch D Circuit High
P1939 Bmw M3 Clutch Pedal Switch A Circuit High
P1939 Mercedes E 430 Accelerometer Front Circuit Failure
P1939 Shanghai Sedan Insufficient Engine Speed Increase During Self Test
P1939 Subaru Stx Lockup Solenoid System
P1939 Mercedes-benz F Class Air Suspension Disable Switch Circuit Open
P1939 Maserati Quatroporte Transmission Fluid Temperature Sensor Circuit High Input