U1791 Diagnostic Trouble Code

U1791 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

Symptoms of a U1791 diagnostic trouble code may include:

Reduction in engine performance, especially at low RPM levels
Vacuum leak on the engine
Diminished fuel efficiency
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.
Dirty air cleaner element Damaged DPF

Repair Processes :

Find out what kind of system you have and verify that voltage to the fuel level sensor is present at the fuel pump wiring harness. If all testing has passed so far yet you still have the same code, check your scan tool and see if it can open and close the IMRC valve.

Process Tips

Diagnostic trouble code U1791 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 U1791.

Fortunately, U1791 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

U1791 Trouble Code For Specific Cars

U1791 Saab 9-2x Ignition Start Circuit Failure
U1791 Talbot Sunbeam Mirror Passenger Right Circuit Failure
U1791 Atalanta V12 Air Temperature Internal Sensor Circuit Open
U1791 Dodge 1500 Ignition Coil A Secondary Circuit Malfunction
U1791 Renault 8 Gear Lever Y Position Circuit Intermittent
U1791 Volkswagen Pointer RightRear Sensor Circuit Short to Vbat
U1791 Lada 1300 Shift Malfunction