← Back to list

2008 Elantra Sedan Fault Codes P0451 and P0420: Causes and Solutions

Model: 2008 Elantra sedan Fault Code: P0420 Posted: 2018-04-13 14:33

Hi everyone, I'm experiencing fault codes P0451 and P0420 on my 2008 Hyundai Elantra sedan. Previously, I had code P0139, which prompted me to replace the O2 sensor located at position 2 (after-treatment oxygen sensor). After installing the new sensor, the P0139 code disappeared, but a new fault code—P0420—appeared. I'm wondering why this occurred and what steps I can take to resolve it. Can anyone provide insight into how these codes relate to each other or suggest troubleshooting procedures for my 2008 Elantra?

Related fault codes
P0420
Comments (3)
Anonymous 2018-04-13 15:16

The P0139 code has resolved, and now you're seeing P0420 and P0451. Is that correct?

Anonymous 2018-05-10 18:00

Actually, I already had P0451 before. When the P0139 code appeared, I replaced the O2 sensor at position 2. After the replacement, the P0139 code cleared, but a new P0420 code emerged. I'm trying to understand why this specific code started appearing after the sensor change.

Anonymous 2018-05-10 22:34

The rear oxygen sensor monitors the catalytic converter's efficiency. After replacing it with a functional sensor, the vehicle’s ECU detects that the catalytic converter is not performing efficiently and triggers the P0420 code as a result. This suggests the converter may be failing or needs further inspection.