I have a 2005 Hyundai Elantra we are getting code P0420 Catalyst system efficiency below threshold bank 1, do you have any idea on what we should check or change first on this car?

Asked by May 24, 2017 at 08:22 AM about the 2005 Hyundai Elantra

Question type: Maintenance & Repair

3 Answers

73,125

Possible causes: Three way catalyst converter Bank 1, Exhaust tube, Intake air leaks, Fuel injectors may be faulty, Fuel injector leaks, Spark plugs may be faulty, Improper ignition timing, Engine Control Module (ECM)....If there is a problem with the engine missing, it would cause the catalytic converters to go bad. Make sure the engine is running correctly. As the code description implies the P0420 code means that the vehicle's control module has detected that the three-way catalytic converter is not working properly (is not as efficient as the factory is expecting). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases the catalytic convert needs to be replaced to fix the problem. If the P0420 code is combined with other codes, try fixing the other codes first.

1 of 1 people found this helpful.

When we bought the car we were told that they just replaced whole exhaust including the catalytic converter, I am guessing they used an after market one. We would have to change that to a Hyundai one? This is the only code that we are getting the last code was for an evap leak and we changed the evap canister in the manifold that code went away and now we are getting this one.

73,125

Try clearing the code out of the computer. Maybe the code was not reset after the exhaust was put on, the computer would store a poxxx code until it is cleared.

Your Answer

Elantra

Looking for a Used Elantra in your area?

CarGurus has 3,508 nationwide Elantra listings starting at $2,490.

Postal Code:

Hyundai Elantra Experts

  • #1
    pittgirl
    Reputation
    1,990
  • #2
    Carrie Shelton
    Reputation
    1,370
  • #3
    tenspeed
    Reputation
    1,110
View All

Related Models For Sale

Used Hyundai Sonata
42 Great Deals out of 1,281 listings starting at $1,781
Used Honda Civic
309 Great Deals out of 4,018 listings starting at $1,411
Used Toyota Corolla
200 Great Deals out of 3,449 listings starting at $1,949
Used Honda Accord
54 Great Deals out of 1,096 listings starting at $1,200
Used Toyota Camry
36 Great Deals out of 1,601 listings starting at $2,400
Used Hyundai Accent
61 Great Deals out of 1,469 listings starting at $1,288
Used Nissan Altima
73 Great Deals out of 1,291 listings starting at $2,750
Used Ford Focus
147 Great Deals out of 2,514 listings starting at $750
Used Mazda MAZDA3
177 Great Deals out of 2,549 listings starting at $1,500
Used Kia Optima
43 Great Deals out of 762 listings starting at $1,239
Used Ford Fusion
162 Great Deals out of 2,048 listings starting at $995
Used Nissan Sentra
171 Great Deals out of 1,718 listings starting at $2,999

Used Cars For Sale

2018 Hyundai Elantra For Sale
500 listings starting at $18,499
2017 Hyundai Elantra For Sale
14 Great Deals out of 1,185 listings starting at $14,990
2016 Hyundai Elantra For Sale
24 Great Deals out of 368 listings starting at $8,950
2015 Hyundai Elantra For Sale
24 Great Deals out of 253 listings starting at $8,485
2014 Hyundai Elantra For Sale
13 Great Deals out of 139 listings starting at $8,888

Content submitted by Users is not endorsed by CarGurus, does not express the opinions of CarGurus, and should not be considered reviewed, screened, or approved by CarGurus. Please refer to CarGurus Terms of Use.