U3791 Diagnostic Trouble Code

U3791 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 U3791 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
Reduction in engine performance, especially at low RPM levels

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.
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 :

With the valve disconnected, the red voltmeter lead should be attached to the IMRC valve power wire and the black voltmeter lead connected to ground. You might continue by connecting the scanner to the vehicle diagnostic connector and retrieving all stored codes and freeze frame data. Replace the oxygen sensor that is downstream from the catalytic converter on the side of the engine that does not contain cylinder #1. Also, if a oxygen sensor code stating "heater circuit malfunction" the sensor has most probably failed.

Process Tips

Diagnostic trouble code U3791 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 U3791.

Fortunately, U3791 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

U3791 Trouble Code For Specific Cars

U3791 Lea-francis Lynx TCIL Circuit Malfunction
U3791 Vauxhall Zafira A Pressure Transducer Redundant / Secondary Signal Faulted
U3791 Tvr 2500 Port Air Circuit Malfunction/ (AIR) System Bank 2
U3791 Proton Tiara Fuel Tank Temperature Sensor Circuit Malfunction
U3791 Subaru R1 LF SIDE REPEATER LAMP OUTPUT Ckt Short to Battery
U3791 Austin 3-litre Autolamp Delay Circuit Open
U3791 Armstrong Siddeley Sapphire Air Suspension Rear Height Sensor High (SE) Signal Circuit Short To Battery