C1939 Diagnostic Trouble Code

C1939 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 C1939 diagnostic trouble code may include:

Fuel pressure too high
Diminished fuel efficiency
Rich or lean exhaust
The light may stay on or light intermittently as the DPF regenerates. The engine will be sluggish on acceleration.

Possible Causes :

Low fuel pressure caused by a clogged filter, failing fuel pump, failed fuel pressure regulator or clogged or leaking injectors.
Low fuel pressure caused by a clogged filter, failing fuel pump, failed fuel pressure regulator or clogged or leaking injectors.
Faulty IMRC actuator relay (if equipped)

Repair Processes :

Look for damage to the tank indicating impact that may have damaged the fuel pump or sender. 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. If the scan tool has that capability, and the scan tool can operate the IMRC valves, then the problem is either resolved and a simple code clearing is all that's left or a new PCM would be called for.

Process Tips

Diagnostic trouble code C1939 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 C1939.

Fortunately, C1939 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

C1939 Trouble Code For Specific Cars

C1939 Vaillante Grand Defi Power Window LR Motor Circuit Short To Battery
C1939 Bmw Concept Climate Control Temperature Differential Circuit Failure
C1939 Aston Martin Ulster Air Suspension Vent Solenoid Output Circuit Short To Ground
C1939 Osca S Door Unlock Disarm Output Circuit Short To Ground
C1939 Mercedes B 200 ABS Hydraulic Pump Motor Circuit Failure
C1939 Dodge R-ft Ignition Run/Start Circuit Short To Battery
C1939 Mercedes Vaneo Air Bag Driver Circuit Resistance Low or Shorted Together