P0157,P0161 - 2003 Kia Sorento

Both codes indicate a a low voltage on the post catalytic converter O2 sensor
Check the wiring to the sensor.
An exhaust leak could also cause these codes to set

Any of the following issues can cause the codes to set
Most likely is a bad connection or faulty O2 sensor

• Air leaks in exhaust in front of o2 sensor giving false reading
• Engine running excessively lean
• O2 sensor connector damaged/corroded
• O2 sensor signal circuit is shorted to ground
• O2 sensor ground circuit is open
• O2 sensor has failed (it may be contaminated with fuel or coolant)
• PCM has failed