Check engine light P0137

OK, 1999 Cherokee Classic with 85k miles. All stock. Real nice shape but keeps posting a check engine with a P0137 on my OBD2 scanner. Replaced downstream O2 sensor. Checked vacuum lines. Checked O2 fuse. Checked both O2 sensor connections for corrosion. Reseated MAP sensor connector and cleaned out throttle body with carb cleaner and Seafoam. Jeep is all tuned up and runs fine. 18 mpg in mixed driving. Exhaust system is good. Very annoying. Anyone with ideas on this?

Thanks, FM

Inspect wiring very carefully for your downstream oxygen sensor.

Thanks, I will check wiring/connector again and report back. I guess there is always a chance the new O2 sensor is bad. I would think not likely though.

Maybe a need to pull the battery cable off to let it re-calibrate?

Inspect the wire harnesses for pinched/damaged wires or chafed/burned insulation. The O2 sensor use the same circuit as the TPS and the Fuel Injectors. Look carefully anywhere the wires can contact the exhaust manifold, the drive shaft, or any sharp sheet metal edges. Check your exhaust manifold for visible cracks at the welds.

If the computer can't see an O2 signal because of a wire issue, it gives the same code as a failed O2 sensor.

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