CEl on ,code PO138

99 XJ 4.0 5 speed. Runs very well. Check engine light just came on. My cheap scanner says P0138 high voltage bank 1 sensor 2
I assume this means the O2 sensor screwed into the cat convertor is faulty?
Better to ask experienced mechanics before replacing parts...

Typical O2 sensor service life is about 125-175,000 miles. They can be tested for proper function.

Inspect the exhaust manifold for cracks,

P0138 JEEP O2 sensor 1/2 Circuit High

Symptoms
- Check Engine Light ON
- High Fuel Consumption
- Excessive Smoke from Exhaust

Possible causes
- Faulty Rear Heated Oxygen Sensor Bank 1
- Rear Heated Oxygen Sensor Bank 1 harness is open or shorted
- Rear Heated Oxygen Sensor Bank 1 circuit poor electrical connection
- Intake air leaks
- Exhaust gas leaks
- Inappropriate fuel pressure
- Faulty fuel injectors

.

"Usually", this code is caused by a faulty downstream (after cat) oxygen sensor. I replaced mine at about 140k because of this code.

If you do replace it, I recommend that you replace both oxygen sensors. If one is failing, the other is not likely far behind. I recommend using NTK brand replacement sensors. Widely available and not that expensive.

I replaced both O2 sensors at about 110,000 miles. Now it has 150,000. I just replaced the rear one and the light stayed off after a 1/2 hour ride.

Will a defective catalytic convertor affect the 02 sensor function?