Catalytic converters reside near the end of your exhaust system and convert harmful
gasses to less harmful ones via chemical reactions, providing increased fuel
efficiency and performance benefits. A failed catalytic converter could lead to misfire
or engine stallage resulting in lower fuel economy or performance for your engine.
Check engine light codes can also illuminate, along with unwelcome rattle-like
noises from within.
P0420
P0420 indicates that your engine computer has identified an issue with your car’s
catalytic converter, which reduces pollution by converting carbon monoxide,
hydrocarbons and nitrous oxide into water, carbon dioxide and nitrogen.
The powertrain control module uses two oxygen sensors – one upstream and one
downstream – to assess catalytic converter performance. If both sensors provide
similar readings, then a check engine light is activated.
P0421
When your engine warms up, your powertrain control module (PCM) stores code
P0421 when it detects that Bank 1 of its warm-up catalyst system is malfunctioning
during engine warm-up conditions. Your PCM uses data from downstream oxygen
sensor and upstream oxygen sensor to gauge catalytic converter performance.
Typically, mechanics begin their evaluation by visually inspecting the exhaust
system before conducting additional tests like sniffing out fumes from the exhaust to
identify excess fuel or testing oxygen sensors while driving the car.
P0422
P0422 indicates that the main catalytic converter system is below its normal
threshold (Bank 1). To determine this catalyst capacity, the powertrain control
module uses temperature and exhaust data from both front and rear oxygen sensors.
A mechanic will start their inspection by checking all wires and connectors around
the catalytic converter to make sure they are undamaged or loose, before searching
for any engine leaks upstream of it.
P0423
This code indicates that the rear oxygen sensor cannot achieve a stable reading of
450mlv due to instabilities in its feed gases, typically caused by unburned fuel,
bypassed coolant or internal chemical mechanisms producing foul odors that cannot
be eliminated through normal combustion processes.
Inside a catalytic converter are precious metals which work to quickly break down
harmful exhaust chemicals, but if contaminated with carbon they become much less
effective at doing this job.
P0424
P0424 error codes occur when there is an abnormal change between oxygen sensor
input and outlet temperatures which falls below an acceptable threshold, prompting
MIL (Malfunction Indicator Light) illumination.
An improper catalytic converter will restrict exhaust flow and make it harder for
engines to receive fresh air in an timely fashion, leading to power-loss issues and
other difficulties during driving.
P0425
This error code indicates that your catalytic converter may be malfunctioning and
driving with this code could pose significant risk to both your engine and exhaust system.
Start by checking for exhaust leaks. A leaking catalytic converter could cause your
car to run lean, throwing off its proper air/fuel ratio and leading to poor fuel economy
and unpleasant smell. Clear the code and drive for about 15 minutes; wait to see if
the code reappears.
P0426
The P0426 code indicates that your powertrain control module has received an
incorrect signal from your catalytic converter temperature sensor, used to assess
engine operating conditions and provide feedback. These sensors are located near
oxygen sensors.
Check your air/fuel mixture, ignition and compression settings are in perfect working
order to avoid fuel and exhaust gases overheating and leading to your catalytic
converter becoming dismantled or blocked up.
P0427
Code P0427 indicates the engine computer has detected poor catalytic converter
efficiency. Before replacing one, ensure a technician inspects oxygen (O2) sensor
readings as well as any physical leakage in your exhaust system – particularly from
manifold and head pipe areas.
Long-term driving with a defective catalytic converter doesn’t pose any direct threat
to drivers; however, it can wreak havoc on engine components. A clogged converter
restricts exhaust flow and forces engines to burn more fuel for acceleration issues
that could impede growth.
P0428
Clogged catalytic converters can cause an unsettling rattle under the car and emit
an unpleasant rotten egg smell in its exhaust system, necessitating further
investigation to ascertain why. Diagnostic tests should be run on both front and rear
oxygen sensors in order to locate what caused their obstruction.
An engine suffering from backpressure due to a blocked catalytic converter can
create backpressure that leads to misfire or even stall. Furthermore, a check engine
light could even illuminate.
P0429
If your vehicle displays the code P0429, it is highly likely that an oxygen sensor or
circuit in the exhaust system has failed. Other possible culprits could include worn
spark plugs, incorrect engine timing or even a catalytic converter with a honeycomb
that has become blocked and melting away honeycomb deposits.
Clogged catalytic converters will restrict exhaust flow and severely limit engine
performance, throwing off air/fuel ratio and leading to misfires or even engine
stalling.