Question about Hyundai Motor 2004 Sonata
Code 121 is for a problem with the circuit for the sensor.
The computer is getting a signal that is out of range, too low or too high.
If you know for a fact the sensor is ok, you may have to check the circuit back to the computer. You would also need a scanner to read the sensor signal.
Posted on Jan 18, 2013
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Posted on Jan 02, 2017
The sensor is located on the left hand rear side of the block (near the bell housing). It is held in place by a 10mm bolt. It's to the right of the exhaust manifold (LH - radiator side) on the V6. Once you purchase the new sensor you'll be able to identify it on the engine. The connector to this sensor is located in the illustration.
A word to the wise... replace the O2 snsr as well.
Posted on Oct 04, 2009
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