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P1491 – What Does It Mean and How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.


P1491 is an OBD-II Code that refers to Exhaust Gas Recirculation Valve Insufficient Lift (Acura, Honda, Isuzu)


A P1491 code is a manufacturer specific diagnostic trouble code related to Acura, Honda, Isuzu vehicles that occurs when the PCM/ECM detects a problem with the exhaust gas recirculation (EGR) valve. The EGR system recirculates a small amount of the exhaust gases back into the engine through the intake manifold. This reduces the amount of NOx emissions from the engine.


The P1491 code will be set when the PCM/ECM detects an issue with the EGR valve not opening far enough or at all.


Common causes for this code include:

  • Bad Exhaust Gas Recirculation Valve
  • Exhaust Gas Recirculation Valve harness is open or shorted
  • Exhaust Gas Recirculation Valve circuit poor electrical connection
  • Exhaust Gas Recirculation Valve clogged
  • Exhaust gas leaks


To diagnose a P1491 DTC code, a technician would:

  1. Scan for codes in the ECM and look at the freeze frame data for failure.
  2. Visually inspect the EGR valve for any signs of damage or debris.
  3. Check the EGR valve operation with a digital volt-ohm meter (DVOM).
  4. Check the EGR system for any blockages or leaks.
  5. Repair or replace any damaged parts as necessary.
  6. Clear the codes and complete a road test to verify repair.

Common mistakes

The following are some of the most common mistakes that a technician may make when diagnosing a P1491 code:

  • Not thoroughly inspecting all the wiring and connectors for damage.
  • Not checking for blockages in the EGR system.
  • Replacing the EGR valve without first checking the electrical circuit.
  • Not properly testing all the components in the system.

How serious is this?

A P1491 code is a moderate problem in terms of severity and should be repaired as soon as possible. If the EGR valve is not functioning properly, it can cause engine starting problems and a loss of power at lower speeds. Additionally, it can lead to decreased fuel efficiency and an increase in emissions.

What repairs can fix the code?

The following are solutions that may fix this problem:

  • Cleaning or replacing the EGR valve
  • Repairing or replacing damaged wiring and connectors
  • Clearing any blockages in the EGR system

Related codes

A P1491 is related to and may be accompanied by the following codes:

P0401 – Exhaust Gas Recirculation System Flow Insufficient

P0402 – Exhaust Gas Recirculation System Flow Excessive

P0403 – Exhaust Gas Recirculation Circuit Malfunction

P0404 – Exhaust Gas Recirculation Position Sensor/Switch Circuit Range/Performance


In conclusion, the P1491 code is a diagnostic trouble code that refers to a problem with the exhaust gas recirculation valve in Acura, Honda, Isuzu vehicles. This code will be set when the PCM/ECM detects an issue with the EGR valve not opening far enough or at all. The most common cause for this code is a bad EGR valve, but it can also be caused by damaged wiring and connectors, or a blockage in the EGR system.