o2 sensors

What brand sensor?

Look for one of these conditions:

A code P0137 may mean that one or more of the following has happened:

Faulty o2 sensor
Exhaust leak near the rear sensor
Plugged catalyst
Short to voltage on O2 signal circuit
High resistance or open on O2 signal circuit

Possible Solutions

Replace faulty sensor
Repair exhaust leak near the rear sensor
Check for restriction in catalyst and replace as necessary
Repair short, open, or high resistance on o2 signal circuit