U2821 Diagnostic Trouble Code

U2821 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 U2821 diagnostic trouble code may include:

Possible spark knock (detonation / pre-ignition)
Poor fuel economy
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
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.
Defective ECU strategies or components will prevent proper regeneration

Repair Processes :

Look for damage to the tank indicating impact that may have damaged the fuel pump or sender. 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. You might continue by connecting the scanner to the vehicle diagnostic connector and retrieving all stored codes and freeze frame data.

Process Tips

Diagnostic trouble code U2821 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 U2821.

Fortunately, U2821 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

U2821 Trouble Code For Specific Cars

U2821 Daewoo Brougham Fuel Trim Malfunction (Bank 2)
U2821 Alvis Firebird Air Bag Tone Warning Indicator Circuit Failure
U2821 Pontiac Sv Four Wheel Drive (4WD) Switch Circuit High
U2821 Volvo S60 Ii
U2821 Dixi 6 IAT Sensor (D/C) Open/Short
U2821 Ambassador Custom Air Suspension Front Compressor Relay Circuit Short To Ground
U2821 Mazda Montrose Turbocharger Boost Sensor B Circuit Range/Performance