P0135: O2 Sensor Heater Circuit (Bank 1, Sensor 1)

What does P0135 mean?

Oxygen sensors only give accurate readings when they are hot. A built in heater warms the sensor quickly after a cold start so the ECM can begin using its signal sooner.

The ECM monitors the heater circuit and how long the sensor takes to start working. When the heater circuit is open, shorted or too slow, it stores P0135.

Common symptoms

• Check engine light on
• Often no other noticeable symptom
• Possible decrease in fuel economy

Common causes

The causes below are the ones commonly seen with P0135. The actual cause can vary by vehicle, engine and mileage, so treat this list as a starting point, not a diagnosis.

• A failed heater element inside the oxygen sensor
• Wiring or connector problems in the heater circuit
• A blown fuse or power supply problem to the heater on some vehicles

What to check with a scanner

• Inspect the sensor wiring for melted insulation or damage near the exhaust.
• Check the related fuse in your service information.
• In Live data, watch how long bank 1 sensor 1 takes to start switching after a cold start.
• Clear the code after the repair and confirm it stays off after several cold starts.

How to read and clear P0135 with OBD Master Pro

1. Plug in your adapter. Connect a generic ELM327 (or ELM329) OBD2 adapter to the diagnostic port, usually under the dashboard on the driver's side. Bluetooth Classic, Bluetooth LE, Wi-Fi and USB OTG adapters are supported.
2. Switch the ignition on. Turn the key to ON or start the engine, depending on your car.
3. Connect in OBD Master Pro. Open the app, go to Connection and pick your adapter. Classic Bluetooth adapters connect from the Bluetooth tab, Bluetooth LE adapters from the BLE tab with no pairing needed. Use the generic OBD2 / EOBD profile or your car's brand profile.
4. Read the codes. Open the fault codes screen to see stored, pending and permanent codes. Confirm P0135 is listed and note any other codes, since they often explain the cause.
5. Check the details. Look at freeze frame data, Live data and, where your car supports it, Mode 06 test results (see the checks above).
6. Fix, then clear. After the repair, clear the codes to turn off the check engine light. Clearing also resets the emissions readiness monitors, so drive normally and check the readiness screen before any inspection. Permanent codes cannot be erased with a scan tool; they clear on their own once the car's self test passes.

Tip: you can also look up P0135 and other codes in the app's DTC search without connecting to a car. If your adapter will not connect, use Connection > Share connection log and email it to support. Many cheap ELM327 clones only handle basic engine OBD2, which is all you need for P0135.

When to see a mechanic

Get professional help if any of these apply:

• The wiring and fuse look fine but the code returns
• You need to measure heater resistance or supply voltage

If you are unsure, a qualified technician can confirm the cause with tests such as smoke testing, pressure testing or scope readings. Clearing a code does not repair the fault.

Related trouble codes

See all OBD2 trouble code guides

Related guides

Check engine light on: what to do · How to read an OBD2 code (P, B, C, U) · Stored, pending and permanent codes and freeze frame · OBD2 readiness monitors explained · OBD2 glossary · OBD2 by car brand