Getting 2 engine codes; PO134 & PO135. What do these codes mean. on 2004 Chevrolet Tahoe

Getting 2 engine codes; PO134 & PO135. What do these codes mean. And what's the estimate cost to repair?

Asked by for the 2004 Chevrolet Tahoe
OX SENSOR HEATER CIRCUIT ISSUES. COULD BE SENSORS OR WIRING ISSUES.SEEK COMPLETE DIAG AS TO NOT WASTE MONEY
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Codes are for the heater circuits on 2 separate oxygen sensors. Suspisious that you 2 go at same time. Could be te sensors themselves. But posssible causes are: Oxygen (O2) Sensor Wiring, Oxygen Sensors, or Powertrain Control Module (PCM)
I cannot help you with cost....need to pin down whats wrong first.u