U0021 Diagnostic Trouble Code


U0021 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 U0021 diagnostic trouble code may include:
  • Misfire
  • Misfire
  • The light may stay on or light intermittently as the DPF regenerates. The engine will be sluggish on acceleration.
  • Rich or lean exhaust
Place of U0021 in engine

Possible Causes :

  • The Mass Airflow sensor will also cause this problem. Mass Airflow circuit malfunction.
  • Fuel with a large percentage of sulfur will clog the DPF quickly
  • An air leak forward of the DPF will change the sensor readings resulting in the code

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. Use the DVOM to test resistance and continuity on all system circuits if actuator and sensor resistance levels are in compliance with manufacturer's specifications.

Process Tips

Diagnostic trouble code U0021 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 U0021.

Fortunately, U0021 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

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