U3781 Diagnostic Trouble Code

U3781 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 U3781 diagnostic trouble code may include:

Poor acceleration
Cherry red hot catalytic converter
Possible spark knock (detonation / pre-ignition)
If the DPF is not cleared the ECU will revert to the "Limp Home Mode" until the situation is corrected

Possible Causes :

A large air leak at or near the number one oxygen sensor would also cause a lean mixture.
Faulty IMRC actuator relay (if equipped)
A faulty oxygen sensor. This will set a code in itself, however, a faulty oxygen sensor does not automatically condemn the sensor. The code just means that the sensor signal was not within specifications. An air leak or any of the above will cause an erroneous signal. There is a multitude of O2 codes relating to O2 performance which gives a clue to the problematic area.

Repair Processes :

You might continue by connecting the scanner to the vehicle diagnostic connector and retrieving all stored codes and freeze frame data. 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.

Process Tips

Diagnostic trouble code U3781 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 U3781.

Fortunately, U3781 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

U3781 Trouble Code For Specific Cars

U3781 Renault Torpedo HO2S Heater Control Circuit High (Bank 1 Sensor 1)
U3781 Morris Cowley Brake Pedal Input Circuit Ground Short
U3781 Gaz 11-73 O2 Sensor Circuit High Voltage (Bank 2 Sensor 3)
U3781 Alfa Romeo 2000 ABS Pump Switch Circuit Failure
U3781 Triumph 2500 Passengers Seat Belt Buckle Switch Circuit Short to Ground
U3781 Riley Mr Hydraulic Base Brake Failure
U3781 Triumph Mayflower PATS Received Incorrect Key-Code From Ignition Key Transponder