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P0139 O2 sensor circuit slow reponse (Bank 1/Sensor 2)

I have a 2003 Hyundai Elantra GLS sedan. Recently the check engine light came on. So, I went to autozone and got the code read - it read ‘P0139 O2 sensor circuit slow reponse (Bank 1/Sensor 2)’. It seemed like it wasn’t trivial to change it (I have only done minor things like changing light bulbs) so I figured that I’ll have to take it to the dealer to get the sensor replaced. The dealer ran his own diagnostics and said that it would cost me $820 to get it fixed…he said we’ll have to replace the sensor and there’s a leak in the rear (I think) exhaust manifold. This car is only worth like $3500 so I definitely don’t want to spend that much money to fix it. What do you suggest I do? Does it really cost that much to fix this sensor? Is it dangerous to drive with this problem?

Take your car to a good independent shop for a second opinion. I believe there is a problem with the O2 sensor because you were able to provide the code. And the shop will hook a scanner up to monitor the O2 sensor to see if it has indeed become lazy.

As far as the exhaust leak? Again, take it to an independent shop and get a second opinion.

Besides, there’s no reason to take a vehicle as old as yours to the dealer for this type of service.


No, it’s not dangerous to drive with this problem. A repair shop should charge you about $110 for a Bosch 13461 rear oxygen sensor. Then, add 1 hour(?) labor charge.
The exhaust might be repaired by welding. The dealer would only replace expensive parts.
Say, “Hello independent shop!”

My daughter had this same code on her Elantra. He husband replaced the rear O2 sensor and this fixed it. However, one of the possible causes for the P0139 code is an exhaust leak. So, it’s possible that a leak in the exhaust manifold could cause the same code. I would get a second opinion from a good independent shop to confirm if there really is an exhaust leak, and then fix the exhaust leak if there is one. I have my doubts, though. The rear O2 sensor is apparently a fairly common failure on the Elantras.

I would expect a leak at the manifold would affect both O2 sensors, not just one.