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

Our certified mechanics come to you · Get a fair and transparent estimate upfront

Red-stars EXCELLENT RATING ON

Cost of diagnosing the P0423 code

P0423 is a diagnostic trouble code (DTC) for "Heated Catalyst Efficiency Below Threshold (Bank l)". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic for $114.99 . Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.0 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.

Cars Estimate Credit towards follow-up repair Earliest Availability
Ford $114.99 $20.0
Toyota $114.99 $20.0
BMW $124.99 $20.0
SCHEDULE P0423 DIAGNOSTIC Get a fair and transparent estimate upfront

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.

Check Engine Light
trouble codes
P0423

No more waiting rooms! Our mechanics will come to you to diagnose and fix the P0423 code.

SCHEDULE P0423 DIAGNOSTIC
Get a $20 credit for the follow-up repair

Recent Check Engine Light is on Inspection reviews

Excellent Rating

(7400)

Rating Summary
6879
249
58
41
173
6879
249
58
41
173
 at YourMechanic

David

13 years of experience
393 reviews
David
13 years of experience
Chevrolet Malibu L4-2.4L - Check Engine Light is on Inspection - Marietta, Georgia
He explained everything to me in detail on what I needed to know about my car. Definitely recommend him for getting the job done.
 at YourMechanic

Raymond

37 years of experience
402 reviews
Raymond
37 years of experience
Toyota Camry L4-2.2L - Check Engine Light is on - Las Vegas, Nevada
Raymond did a great job however I was charged for two hours labor and he was only here less than 45 minutes. should I expect this on future appointments with your mechanic ?
 at YourMechanic

Shane

17 years of experience
217 reviews
Shane
17 years of experience
Volkswagen EuroVan V6-2.8L - Check Engine Light is on Inspection - Austin, Texas
Arrived on time. Explained the issues he found and how he will fix it. I have parts on order and will schedule an appointment to have Shane install the parts when they arrive.
 at YourMechanic

Kanstantsin

19 years of experience
51 reviews
Kanstantsin
19 years of experience
Ford F-150 V8-4.6L - Check Engine Light is on Inspection - Littleton, Colorado
Kanstantsin arrived early. Was very courteous and professional. Will highly recommend to anyone. Thank you Kanstantsin.


More related articles

P2234 OBD-II Trouble Code: O2 Sensor Signal Circuit Shorted to Heater Circuit Bank 2 Sensor 1
P2234 P2234 code definition O2 Sensor Signal Circuit Shorted to Heater Circuit Bank 2 Sensor 1 What the P2234 code means Code P2234 is an OBD-II generic code for the Engine Control Module (ECM) detecting the O2 sensor signal wire...
P0487 OBD-II Trouble Code: Exhaust Gas Recirculation Throttle Control Circuit A
P0487 code means that the car’s computer did not register the correct amount of air pressure in the manifold due to malfunction.
P0659 OBD-II Trouble Code: Actuator Supply Voltage "A" Circuit High
P0659 means there is an issue or malfunction with the actuator supply voltage "A", which may be caused by faulty wiring or control module issues.

Related questions

Car won't let me accelerate.
Hello there, A continued oxygen sensor and voltage code is a sign there is still a problem with your 2002 Pontiac Firebird. You did not say if you replaced the oxygen sensor in question or not. I am going to...
My Pontiac G6 won't crank and wont start
I believe your "no crank" issue is the passlock security system has locked things down because of what it perceived as a "battery swap". If the car restarted after the jump as you indicate, the ECM is probably OK. The...
P2006 code is present in the computer.
Hi there. With having the code P2006 (https://www.yourmechanic.com/article/p2006-obd-ii-trouble-code-intake-manifold-runner-control-stuck-closed-bank-1-by-spencer-clayton) present, check the intake wiring to the runner control and see if there is a good connection. Also, the runners in the intake could be clogged and needs cleaned out. A leaking...

How can we help?

Our service team is available 7 days a week, Monday - Friday from 6 AM to 5 PM PST, Saturday - Sunday 7 AM - 4 PM PST.

1 (855) 347-2779 · hi@yourmechanic.com