P0135 — O2 Sensor Heater Circuit (Bank 1, Sensor 1)
Drive with caution — fix soon.
What P0135 means
P0135 means the heater circuit built into the upstream oxygen sensor on Bank 1 isn't drawing the expected current. Modern sensors have a small internal heater so they reach operating temperature quickly; when it fails, the sensor is slow to work at cold start. The fix is often a new sensor, but a blown fuse or bad wiring can also be to blame.
Common symptoms
- Check engine light on
- Poorer fuel economy right after cold starts
- Failed emissions test
- Possible rough running when the engine is cold
- Often no noticeable change once warmed up
Common causes
- Failed heater element inside the oxygen sensor
- Blown fuse for the sensor heater circuit
- Damaged or corroded wiring or connector
- Poor ground or open in the heater circuit
- Relay or power-supply fault feeding the heater
- Water or road salt intrusion at the connector
Typical repair cost
$150 – $450
Varies by vehicle and root cause.
Frequently asked questions
Can I drive with a P0135 code?
Yes, short-term driving is usually fine, especially once the engine warms up. Fix it soon so cold-start emissions and fuel economy return to normal.
How much does it cost to fix P0135?
Replacing the oxygen sensor typically costs $150-$450 with labor. If it's just a blown fuse or a wiring repair, it can be considerably cheaper.
Is P0135 serious?
It's moderate. The car still drives, but the sensor heater fault affects cold-start performance and will fail an emissions test.
What does the heater in an oxygen sensor actually do?
It quickly warms the sensor to operating temperature after start-up so it can read the exhaust accurately right away, rather than waiting for engine heat.