DIY job or brace for shop bill?... p1135 computer readout

Car seems to be running great but got p1135 readout. A)what is the problem? guessing something with the o2 sensors…b)I’ve got basic diy skills (brakes, oil change, plugs, ignition coils etc)…is this a diy job for me or should I brace myself for a shop bill?

Make model and year please. Number of miles would also be a good idea.

Should be:

P1135 for an OBD 2 Toyota is:

P1135 Air/Fuel Sensor Heater Circuit Response. (Bank 1 Sensor 1)

This is your O2 sensor. I would have the sensor tested before replacement. You will need to get a repair manual for your year of car to get testing procedure. It’s simple to change out if it is needed.
Repair manual will also tell you which sensor it is if it has more than one.