P1491 - FAULT CODE - OBD2

POST UPDATED IN February, 2023

P1491 Code failures by brands

P1491 ACURA, HONDA, ISUZU: EXHAUST GAS RECIRCULATION VALVE INSUFFICIENT LIFT

Description of DTC code P1491

In many countries around the world, NOx emissions from diesel and gasoline vehicle engines are restricted. This is a harmful compound formed by the combustion chamber of the engines.

Manufacturers have implemented a NOx emission reduction system due to the reasons exposed above. This process is known as EGR (Exhaust Gas Recirculation). Its design achieves a proportional and controlled recirculation of engine exhaust gases into the intake air. Typically, a valve is used to control the passage of the gas, and the valve closes completely if possible.

The EGR valve includes a sensor that detects the amount of valve lift. The command value for lift is pre-stored in the PCM (Powertrain Control Module) so that gas recirculation can be optimized based on driving conditions. By comparing this command value with the output signal value of the EGR valve position sensor, the PCM adjusts the valve so that the actual lift amount equals the command value.

If the EGR Valve Position Sensor output signal value has wide differences from the commanded value in the PCM memory over a given period, it is interpreted as an EGR valve or position sensor fault, giving way to the P1491 OBDII fault code setting.

Symptoms of fault code P1491

  • Check Engine light on.
  • Difficult start of the engine.
  • Unstable idle speed.
  • Loss of motor power at low speeds.
  • Decreased fuel efficiency.

Causes of OBD2 P1491

The P1491 OBD2 DTC P1491 is stored by one or more of the following reasons:

  • The valve harness of the Exhaust Gas Recirculation system may be damaged causing a short or open circuit.
  • There may be exhaust leaks.
  • The EGR valve may be clogged or defective.

Possible solutions of the DTC code P1491

To resolve the P1491 OBDII diagnostic code, consider the following:

  • Consult Technical Service Bulletins.
  • Check the EGR valve wiring and check for damage such as wear, corrosion, or burns. Repair or, if necessary, replace the damaged components.
  • Make electrical checks on the valve circuit of the Exhaust Gas Recirculation If one of the circuit voltages differs from those specified, fix them.
  • Check the system for exhaust leaks. Adjust any connections or repair as necessary.
  • Check the EGR valve for proper operation. Follow the manufacturer's recommended diagnostic steps. If you determine that it is defective, replace it.

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