I have a 98 kia sportage. ck eng light said i needed o2 sensor. replaced the sensor. ck eng light returned after clearing codes with scanner. ck eng light is still on but no codes show on the scanner.

Code 038 means the computer is getting a high voltage return in the heater circuit from the O2 sensor mounted after the catalytic converter. The O2 sensors have an internal heater to make them work as soon as you start the engine.
You would need to test the circuit to and from the sensor to find the real problem.

The O2 sensor is most likely the issue. Also, try cleaning the Throttle Body Injector with cauberator cleaner or tbi injector. Build up within the TBI may be causing a gas deficiency which causes it to run lean. If that doesn't help, try running a higher octane fuel, about 93 octane minimum. This will causes ANY debree in the injectors to be cleared.

O2 or HO2S
that is the question
O2 sensors are after the cat converter/s where as HO2S sensors are in the exhaust manifold before the cat converter/s and report exhaust gas composition to the ECM so that the air /fuel mixture can be adjusted
May be you replace the wrong sensors

I called Kia about my check engine light and I told them my mechanic
read the computer and it says 02 sensor. She told me Kia does not sell out there codes to the computer in our cars and that I would have to take it to a Kia repair shop to get the correct reading form the computer

For oxygen sensor location diagram on kia sportage, click the link below:---

http://technoanswers.blogspot.com/2012/12/o2-sensor-located-in-2005-kia-sportage.html

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These will help.
Thanks.

Replace O2 sensor, this isnt expensive and generally solve the problem; if you note the code number, send it us.

Hi.

When the check engine lights comes on there are codes stored in the ECU module (car main computer.
To know what must be replaced you need to find out what codes are stored in the ECU.
Post 1995 codes adhere to OBDII standard (see here: Kia OBD-II Trouble Codes). The codes can be retrieved connecting the ECU to a code scanner (like this:Actron CP9575), and performing a scan.
If you live in the US, code scanning can be done for free at the nearest Autozone, otherwise you can have a code scanning done at your garage for a small fee.

Regarding the mechanic's suggestion of replacing the cat convertor and oxygen sensor, that is probably based on testing. If the mechanic has checked the emissions, and emissions are hight though the engine is OK, then it may time to replace the cat converter. The mechanic can also decide to replace the cat converter if the part is not in good shape.

If the decision is based on an O2 sensor OBDII code,before replacing the sensor better having a quick look at emission and engine.

The best way to proceed is generally determined by the code returned and by the checkup of state of the engine, O2 sensor, and exhaust system.

Regards.

Ginko.

o2 sensors are bad.will make it run rich

Yes. 1 is a bad O2 sensor and the other a mis-fire.

Best thing to do is a major tune up (replace plugs/wires/fuel filter/PCV valve/etc...) and also replace the Bad O2 sensor.

Running it like this can cause long term damage. Let alone you are losing gas milage as well.

Good luck.

Ok I think you meant code P0171, this means the fuel trim is always lean, you need to check for a engine vacum leak, maybe a cut or damaged PCV hose or any other hose that is in the vaccum system, I have read other Kia owners (Kia Forums, you should join one) reports of this same code, most found it not to be the O2 sensor but a vacuum leak.