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P0139 OBD2 Code Recurring in 2002 Hyundai Elantra GLS (Auto, 99K Miles)

Model: 2002 Hyundai Elantra GLS Fault Code: P0139 Posted: 2011-07-26 16:14

I recently encountered the P0139 diagnostic trouble code on my 2002 Hyundai Elantra GLS with automatic transmission and 99,000 miles. The code is commonly associated with a rear oxygen sensor issue. I replaced both the front and rear O2 sensors with NTK parts, as they were the original factory-installed sensors at that mileage. During the initial service, the shop inspected the exhaust flex pipe and confirmed no damage or leaks in the emission system. After resetting the ECU via OBD-II, the code disappeared—but returned approximately 200 miles later. I'm now wondering if there's another underlying cause beyond sensor failure. Any insights from owners of similar models with this exact code?

Related fault codes

P0139

Comments (4)

Anonymous 2011-07-26 20:16

Are you certain that NTK is the original factory brand for your vehicle's oxygen sensors? Some OEM parts are specific to model years and trim levels.

Anonymous 2011-07-27 08:05

I don't remember the exact brand of the original sensors, but I'm confident that the NTK units I installed are compatible with my 2002 Hyundai Elantra GLS. Before investing further in sensor replacements or repairs, I plan to try resetting the ECU by disconnecting the battery for a short period and monitor whether the P0139 code reappears.

Anonymous 2011-08-20 22:18

I currently have a P0455 code on my 2002 Hyundai Elantra—could be related to evaporative system issues, but different from your O2 sensor problem.

Anonymous 2011-08-21 07:41

Resetting the ECU by removing fuses 10 and 25 (for a brief period) appears to have resolved the issue. I've driven over 300 miles since, and the check engine light for P0139 has not come back.