Skip the auto shop - Our mechanics make house calls

Q: Po420 bank1

asked by on

My van runs great when I started I get a knock which gets better as it warms up, my fuel trims seem to be high.ltft. I clear the code but after about 40 miles it comes on again. Thx tom

My car has 125000 miles.
My car has an automatic transmission.

A: Hello Tom. P0420 is the Catalyst System Eff...

Hello Tom. P0420 is the Catalyst System Efficiency Below Threshold (Bank 1) code. While there are a multitude of components that can cause this code, the general concept is that your catalytic converter is not working properly. If you suspect the catalytic converter is not to blame, then the oxygen sensor after the catalytic converter may not be working correctly. The only option at that point is to replace the sensor. You will also want to visually inspect the exhaust system. Check for any cracks, holes, discoloration, and even tap on the catalytic converter to see if there is a rattle inside. A hole, crack, or dent would restrict the flow of exhaust and give false readings to your sensors. As well as stress the engine, as it will try and compensate for the changes. When tapping on the catalytic converter, you are listening for a rattle or indication that the converter has failed and come apart on the inside. Again, check for any signs of damage, and start by replacing the oxygen sensor if needed. Turn to the catalytic converter next if the issue continues.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Save up to 30%

Get a quote

What others are asking

Q: Coolant compatibility in f350.

Hello. I am not sure why they put Dexcool into your cooling system. Your truck requires the specific Ford coolant due to the design of the engine. There really is no reason why Dexcool should have been used, and if...

Q: What tips and steps should I follow to care for the CD player?

While your car’s CD player is designed to be largely maintenance free, there are a few things that you’ll need to know about care and maintenance. Follow the tips below: Don’t insert discs with damaged or peeling labels. Don’t...

Q: fuel volume regulstorcontrol circuit /open

Hi there. The fuel pressure volume regulator control circuit/open requires circuit test be performed. A scanner would help for monitoring the parameter. The fuel pump could be at fault, with little or no fuel pressure, the PCM (powertrain control module)...

Related articles

How to Renew Your Car Registration in Oklahoma(DELETED)
Having your car registered with the Oklahoma Tax Commission is an important part of driving legally in this state. You will need to do this within 30 days of moving to Oklahoma...
P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the P0052 code means This code is seen when the Engine Control Module (ECM) tries to control the...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...