Skip the auto shop - Our mechanics make house calls

Q: Check Engine Light P0420 trouble code

asked by on

i have 2011 nissan altima. About a month ago the CES light came on and was on for about two weeks. I just purchased a new transmission less than 5 months ago so I thought there may be an issue with it. It took it back to the dealership immediately. They ran a diagnostic check on it and informed me that the error code is PO420, and that I may be able to get it repaired cheaper at a muffler shop. However, I have not had the income to get it repaired yet. A week later the CES light went off by itself. Now, three weeks later it has come on again. Could something other than the catalytic converter be causing the CES light to come on?

My car has 138000 miles.
My car has an automatic transmission.

A: Hi there, thanks for writing in. Typically,...

Hi there, thanks for writing in. Typically, a P0420 code (catalyst efficiency insufficient) is the catalytic converter not properly functioning. Chances are, the Check Engine Light going off and then back on, it's still the P0420 code that is present. An exhaust leak(s) and rarely O2 sensor faults, can also cause this code to set. To avoid any unnecessary repairs, I recommend having your vehicle's P0420 trouble code be diagnosed and repaired by a certified technician, such as one from YourMechanic.

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: Bad catalytic converter

Hello. Typically using chemicals to solve a catalytic converter issue will only prolong the issues from getting worse. These products are not necessarily intended to be used as a fix, but as an additive to an engine that is working...

Q: How to find and stop cause of engine vibration?

Usually engine vibration is due to a misfiring cylinder, and a Check Engine Light will be usually be triggered. It may be possible that the vibration is caused by a low idle speed and by turning on the AC, it...

Q: My truck turns over but won't start.

When a truck won't start, it's usually going to be an ignition or fuel system-related malfunction. The fact that your gas gauge was "ticking" a bit may be an indicator that an electrical problem exists, causing the ignition system to...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...