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

What does P0135 mean?

This is a heater fault, not a signal fault. Each modern O2 sensor has a small built-in electric heater that brings it up to operating temperature quickly after a cold start. The computer has found the heater circuit for bank 1, sensor 1 (upstream) open, shorted, or drawing the wrong current.

Generic OBD-II definition: O2 Sensor Heater Circuit (Bank 1 Sensor 1). Confirm applicability in your vehicle service information.

Common causes

• Heater element inside the sensor burned out (very common; the sensor must be replaced)
• Blown fuse feeding the O2 heaters
• Broken power or ground wire to the heater
• Corroded connector

Symptoms

• Check engine light, usually with no drivability change
• Slightly higher emissions and fuel use during warm-up

Can I keep driving with P0135?

Severity: Low Usually safe to keep driving, but get it checked.

If the check engine light is flashing or the car runs badly, stop driving and have it checked.

Typical fixes

• Check the O2 heater fuse in the fuse box
• Measure the heater resistance across the sensor's heater pins (compare to the service spec)
• Verify the heater has battery voltage with the key on
• Replace the sensor if the heater element reads open