Skip the auto shop - Our mechanics make house calls

P0423 OBD-II Trouble Code: Heated Catalyst Efficiency Below Threshold (Bank l)

check engine light logo

P0423 code definition

Heated Catalyst Efficiency Below Threshold (Bank l)

What the P0423 code means

P0423 is an OBD-II generic code that the engine control module (ECM) got input from the heated catalyst efficiency sensor for bank 1 that the catalyst is below efficiency levels programmed in the ECM.

What causes the P0423 code?

  • The bank 1 catalyst has lost its efficiency or has broken apart inside and needs replaced.

  • The air injection system is not pumping the correct amount of air or too much air into the bank 1 catalyst due to a fault in the air injection system.

  • The O2 sensor post catalyst on bank 1 is not working to specifications.

What are the symptoms of the P0423 code?

  • The Check Engine Light will be illuminated and the code is set in ECM memory and freeze frame.

  • The engine may not have any drive symptoms except a check engine light is on unless the catalyst is damaged and clogging the exhaust. Then all the symptoms of a blocked exhaust will be encountered like loss of power and misfiring.

How does a mechanic diagnose the P0423 code?

  • Scans codes and documents the freeze frame data in order to verify the problem

  • Clears the engine codes and retests the air injection system for proper operation

  • Checks the catalyst and sensor for any signs of damage or leaking joints in the exhaust

  • Scans the O2 sensors to see if the pre and post sensors are reading the same indicating a catalyst is broken apart

  • Checks the air injection pump for proper operation to the bank 1 catalyst

  • Compares bank 1 and bank 2 pre and post catalyst to isolate a bad sensor

Common mistakes when diagnosing the P0423 code

  • Not checking for proper operation of the air injection pump before replacing the catalyst or post O2 sensor.

  • Not checking the exhaust system for leaks before the O2 sensors before replacing the O2 sensor.

How serious is the P0423 code?

  • The post O2 sensor gives an indication of a problem with the catalyst and this could lead to a blocked exhaust system or damaged engine components from excessive back pressures.

  • The Check Engine Light being on causes the vehicle to fail emission testing.

  • The emission output levels may be above legal limits.

What repairs can fix the P0423 code?

  • Replacing the post O2 sensor for bank 1
  • Replacing the catalyst on bank 1
  • Repairing the wiring to the O2 sensors if they got burnt on the exhaust

Additional comments for consideration regarding the P0423 code

Code P0423 is a problem with the catalyst for bank 1 and the most common failure is the post O2 sensor not responding or slow to respond to changes in the exhaust O2 levels.

Need help with a P0423 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

Post a question and get free advice from our certified mechanics.

ASK A QUESTION

More related articles

How to Renew Your Car Registration in Oklahoma(DELETED)
Having your car registered with the Oklahoma Tax Commission is an important part of driving legally in this state. You will need to do this within 30 days of moving to Oklahoma...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
Insurance Requirements for Car Registration in Kentucky
The Kentucky Transportation Cabinet requires that all drivers in Kentucky carry liability automotive insurance, or “financial responsibility” in order to operate a vehicle legally and maintain vehicle...


Related questions

Q: Check Engine Light with code P0740

There are a number of symptoms that may accompany a P0740 code, it may be that your car will stall at stop lights, or have trouble shifting, or you may not notice anything at all except your gas mileage is...

Q: Car in limp mode, check engine light on

In this case you should have an experienced technician look at the vehicle. Limp mode is usually a term used for a vehicle with an automatic transmission which stays in second gear when certain faults arises. A certified technician, like...

Q: Car cranks over but won't start - 2004 Nissan Sentra

If the fuel pump is not "whirring" momentarily when you turn the key "on", either the pump is not receiving power or it's non-functional. You might try probing the fuel pump harness for 12 volts at moment key is turned...