It is the sensor that is screwed into the exhaust manifold on the back of the engine.
If it is saying that the heater circuit has failed then this O2 sensor has failed. The o2 sensors have tip heaters in them. These are irreplaceable. Replace the whole sensor. This particular sensor is located on the driver's side exhaust in front of the Catalytic Convertor.
Trouble code P0135 means:O2 sensor heater circuit malfunction (Bank 1 Sensor 1)
heater sensor circuit Chevy astro 2000
9 time out of 10, the heater circuit internal to the sensor has failed. Replace the sensor.
Oxygen (A/F) Sensor Heater Control Circuit High (Bank 1 Sensor 1)symptomsOther than the MIL light illuminating you may not notice any performance issues.causeA short in the O2 sensor heater circuit or the sensor itselfA faulty O2 sensor heaterWiring or connectors are broken or frayed to the sensor or relayBad PCM or ECMThe fixCorrect wiring short or loose connector found in inspection.and/orReplace the bank 1 sensor 2, O2 sensor
Oxygen (A/F) Sensor Heater Control Circuit High (Bank 1 Sensor 1)symptomsOther than the MIL light illuminating you may not notice any performance issues.causeA short in the O2 sensor heater circuit or the sensor itselfA faulty O2 sensor heaterWiring or connectors are broken or frayed to the sensor or relayBad PCM or ECMThe fixCorrect wiring short or loose connector found in inspection.and/orReplace the bank 1 sensor 2, O2 sensor
left side of the engine after the cat
Oxygen (A/F) Sensor Heater Control Circuit High (Bank 1 Sensor 1)symptomsOther than the MIL light illuminating you may not notice any performance issues.causeA short in the O2 sensor heater circuit or the sensor itselfA faulty O2 sensor heaterWiring or connectors are broken or frayed to the sensor or relayBad PCM or ECMThe fixCorrect wiring short or loose connector found in inspection.and/orReplace the bank 1 sensor 2, O2 sensor
Heated oxygen sensor heater circuit malfunction (bank 1, sensor 1): Open or short in heated oxygen sensor heater circuit Heated oxygen sensor heater malfunction (Haynes Repair Manual)
Oxygen (A/F) Sensor Heater Control Circuit High (Bank 1 Sensor 1)symptomsOther than the MIL light illuminating you may not notice any performance issues.causeA short in the O2 sensor heater circuit or the sensor itselfA faulty O2 sensor heaterWiring or connectors are broken or frayed to the sensor or relayBad PCM or ECMThe fixCorrect wiring short or loose connector found in inspection.and/orReplace the bank 1 sensor 2, O2 sensor
O2 sensor Heater Bank 1 Sensor 1
is located in the exhaust manifold .every time is to much better change the 2 sensor atone time