P0423 Code - Heated Catalyst Efficiency Below Threshold Bank 1

What Does P0423 Mean?

The Engine Control Module (ECM) monitors the switching frequency ratio of heated oxygen sensors 1 (front O2 sensor) and heated oxygen sensors 2 (rear O2 sensor).

A three way catalyst converter (Manifold) with high oxygen storage capacity will indicate a low switching frequency of heated oxygen sensor 2. As oxygen storage capacity decreases, the heated oxygen sensor 2 switching frequency will increase.

When the frequency ratio of heated oxygen sensors 1 and 2 approaches a specified limit value, the three way catalyst malfunction is diagnosed.

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What are the common causes of P0423 ?

The most common cause of this code is due to a faulty catalytic converter. Bad oxygen sensors are also a possibility but if this is the case an oxygen sensor code will usually accompany the catalytic converter code. Always diagnose and repair oxygen sensor codes before attempting to diagnose catalytic converter codes. Since the catalytic converter is not designed to wear out, its failure is normally associated with some contributing malfunction. Contributing factors in catalytic converter failure may include incorrect fuel usage, excessive fuel being dumped into the exhaust system due to a faulty coolant temperature sensor, mass air flow sensor, manifold air pressure sensor, fuel pressure regulator, or fuel injection component, an ignition misfire, retarded spark timing, or oil contamination. Leaks from an exhaust manifold, down pipe, flex hose, or other exhaust component that is upstream from the catalytic converter can also appear to the PCM as catalytic converter failure.



How do you troubleshoot P0423 ?

If the engine displays a miss and there wasn't a code, determine which cylinder is misfiring. If the exhaust manifold is visible, spay or pour a small amount of water on each cylinder exhaust port. Water will evaporate immediately on good cylinders and slowly on the missing cylinder. If this can't be accomplished pull the plugs and check the condition. If all testing has passed so far yet you still have the same code, check your scan tool and see if it can open and close the IMRC valve. Look for damage to the tank indicating impact that may have damaged the fuel pump or sender.

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