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

74,725

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.

74,725

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 3,534 nationwide Elantra listings starting at $2,650.

Postal Code:

Hyundai Elantra Experts

  • #1
    pittgirl
    Reputation
    2,000
  • #2
    Carrie Shelton
    Reputation
    1,390
  • #3
    tenspeed
    Reputation
    1,130
View All

Related Models For Sale

Used Hyundai Sonata
46 Great Deals out of 1,394 listings starting at $1,490
Used Honda Civic
295 Great Deals out of 3,143 listings starting at $995
Used Toyota Corolla
253 Great Deals out of 4,072 listings starting at $1,840
Used Toyota Camry
94 Great Deals out of 2,281 listings starting at $1,781
Used Honda Accord
80 Great Deals out of 910 listings starting at $1,411
Used Hyundai Accent
76 Great Deals out of 1,518 listings starting at $1,495
Used Nissan Altima
89 Great Deals out of 1,414 listings starting at $1,785
Used Kia Optima
60 Great Deals out of 923 listings starting at $6,195
Used Ford Focus
87 Great Deals out of 2,605 listings starting at $999
Used Mazda MAZDA3
162 Great Deals out of 2,807 listings starting at $995
Used Nissan Sentra
200 Great Deals out of 1,778 listings starting at $1,995
Used Ford Fusion
182 Great Deals out of 2,067 listings starting at $995

Used Cars For Sale

2018 Hyundai Elantra For Sale
816 listings starting at $15,741
2017 Hyundai Elantra For Sale
26 Great Deals out of 802 listings starting at $11,995
2016 Hyundai Elantra For Sale
43 Great Deals out of 458 listings starting at $8,767
2015 Hyundai Elantra For Sale
17 Great Deals out of 264 listings starting at $9,395
2014 Hyundai Elantra For Sale
18 Great Deals out of 169 listings starting at $7,887

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.