The P0421 fault code indicates that the catalytic convert is not heating. The catalytic convert closest to the engine is referred to as Bank 1. This fault code is not found in most vehicles. The most common Mazda and Mitsubishi models have this code. This is usually between five and ten minutes following the initial start of the vehicle.
The ECM/PCM compares two values using data from oxygen sensors upstream and downstream. The engine fault light will come on if both values are very close or the same. The P0421 code is recorded if this problem only occurs when the vehicle first starts up and warms up.
The catalytic convert is mounted within the exhaust system, and it resembles an ordinary silencer. In two-row engines there are more than one catalytic convertor. When the converter works properly, it converts the pollutants from the engine into water vapour and CO2.
Table of Contents
What are the causes of fault code P0421?
- Faulty catalytic converter, Bank 1
- Faulty oxygen sensors
- Problems with the oxygen sensor, such as broken wires or bad connections
- Exhaust leak
- ECM/PCM Faulty
What are the symptoms of fault code P0421?
- The engine fault light will illuminate (in some cases, no other fault indication may be visible)
- The engine will not start
- Engine performance drops or a hesitation in acceleration
- Odours coming from exhaust
How to Fix Fault Code P0421?
The mechanic should visually inspect the exhaust system if the P0421 is the only code in the system. The mechanic should perform a road test and smell the exhaust fumes. They should also check the catalytic convert to see if it is glowing. The PCM and oxygen sensors can be tested if the vehicle passes the tests. The customer should request that the oxygen sensor be replaced if it is defective. The biggest mistake in diagnosing the code P0421 is replacing the catalytic convert without doing all the tests. The P0421 code is not caused by this. All possibilities should be considered.
- Replacement of the catalytic converter
- Replace the oxygen sensor if it is faulty
- Repair or replace cables that are associated with the oxygen sensors
- Replacement the powertrain module
How serious is fault code P0421?
The severity of the fault code P0421 depends on the circumstances. When the engine or catalytic convertor is malfunctioning, driving the vehicle can result in serious engine damage. For an engine to function properly, it needs to be able to breathe. The engine won’t run properly if the catalytic convertor’s internal parts have melted, or clogged up with carbon deposits.
