P0091 Diagnostic Trouble Code


P0091 is a kind of OBD-II Diagnostic P-Powertrain 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 P0091 diagnostic trouble code may include:
  • Fuel pressure too high
  • Diminished fuel efficiency
  • Rich or lean exhaust
  • Engine surge
Place of P0091 in engine

Possible Causes :

  • Rusty exhaust systems, cracked exhaust manifolds or damaged or missing gaskets or donuts will cause air leaks.
  • An air leak forward of the DPF will change the sensor readings resulting in the code
  • Faulty IMRC actuator relay (if equipped)

Repair Processes :

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. Look for rubbing, scraping, bare wires, worn spots or melted plastic connectors. Pull the connectors apart and carefully look at the terminals (the metal parts) inside the connectors. Look for damage to the tank indicating impact that may have damaged the fuel pump or sender.

Process Tips

Diagnostic trouble code P0091 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 P0091.

Fortunately, P0091 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

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