My 307cc pug mark 2 55 plate P0135....O2 Sensor Heater Circuit (Bank 1 Sensor 1)

SOURCE: diagnostic code p0135

What engine is in this vehicle? I assume the avalon would be a 3.0L or similar V6 engine. Bank 1 sensor one indicates one of the primary O 2 sensor controlling a/f ratio. Sensor one bank one would be the sensor located in the Front manifold, closest to the engine. Hope this solves your issue. I would first check the conector at this sensor for corrison before buying a new sensor.

SOURCE: 1999 dodge dakota p1762 code

dont know lots about this witout engine size but some have 1 coil per cylender possible coil is bad or plug 02 sensor will cause some problems but a miss fire will cause it to run like trash

SOURCE: more 99 cougar problems

there is a fuse for the o2 heaters if one of the sensors blew the fuse they will all be out

SOURCE: P0155 & P0135

O2 sensors are tricky. sometimes like anything else they fail. many times though the exhaust mixture they encounter is out of their range and that shows up as a failure.since you seem to have no other problems , I would go ahead and change them, but don't be disappointed if the code shows up again (at least you know it's not the sensors.) I don't like using the process of elimination when doing repairs but sometimes you must.

SOURCE: obd code P0135 on a lexus ls400

usually your first sensor is located on the exhaust manifold