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P0424 – 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.


Heated Catalyst Temperature Below Threshold (Bank 1)


P0424, Catalyst System Efficiency Below Threshold (Bank 1), indicates that the PCM has detected a condition where the engine is not operating properly or there are some problems with the Catalytic Converter. Usually, this code is accompanied by P0420 (catalyst system efficiency below the threshold for bank 2). 

This particular check engine light usually comes on suddenly, which may mean there is some sort of an issue with one of the fittings on the exhaust system or something similar. The more likely case is that there are several small issues building up, causing small amounts of damage over time, until they finally make enough problems to trigger this error.


P0424 codes are stored by the PCM because of these causes.  Among them are:

  • Stuck/blocked venturi in the high-pressure fuel pump 
  • Fuel leak at high-pressure fuel pump or low fuel pressure regulator connection 
  • Fuel injectors harness is open or shorted 
  • Wiring issue between PCM and Relay Control Module (RCM) or Powertrain Control Module (PCM) relay faulty 
  • Powertrain Control Module (PCM) has failed.


  • Engine Light ON (or Service Engine Soon Warning Light)
  • Possible Excessive Emissions and Poor Fuel Economy


To diagnose P0424 OBD code your vehicle needs to be scanned with a factory scan tool or equivalent. 

The first step should be to address any codes related to engine misfires, oxygen sensors, or fuel trim. A P0424 error code could result from one of these causes. The mechanic will then test the oxygen sensor and check for air leaks after ruling out one of these codes. Replacing the catalytic converter is the only option if the code is still present on retests.

Common mistakes

In diagnosing a P0424 error code, the most common mistake is failure to resolve other codes first. Catalytic converter failure can also be caused by these other codes, such as a repeated failure of a catalytic converter. By not addressing them first, costly mistakes may be made and the vehicle may suffer even more damage.

How serious is this?

A P0424 code may not cause noticeable changes in your car’s behavior, but it can cause serious problems when it comes time to pass the OBD-II emissions test. Failure of a catalytic converter not only increases the vehicle’s emissions, but if the code remains unresolved, the Check Engine light will continue to illuminate, and the vehicle will not pass emission tests.

What repairs can fix the code?

Typically, after any other codes have been resolved, the catalytic converter must be replaced to resolve the code. Even so, there may be other ways to solve this issue, including:

  • Removing and replacing the oxygen sensor
  • Preventing a catalytic converter air leak
  • Replacement of the PCM (rare)

How much does it cost to fix the P0309 code?

The expert mechanic will test for air leaks and test the oxygen sensor. Replacing a catalytic converter can cost around $800, depending on where you go.


The P0424 code is a common OBD-II trouble code that can be triggered by many different things. It’s important to know the cause of your specific problem so you can diagnose and fix it, but in general, it may mean there’s either an issue with the catalytic converter or oxygen sensor downstream from the catalyst. If you’re getting this error, we recommend taking your car for a tuneup before going further down any rabbit holes! Let us assist you with diagnosing and fixing any issues with your vehicle.

P0424 – What Does It Mean and How To Fix It