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?
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