Fault-Code Library · Oxygen sensing
P0135: Oxygen sensor heater circuit, bank 1 sensor 1
The upstream oxygen sensor heater circuit is not operating as expected.
Common symptoms
- •Engine warning light
- •Poor cold-start emissions
- •Delayed closed-loop fueling
- •Fuel economy change
Likely causes
- •Failed oxygen sensor heater
- •Blown fuse
- •Wiring near exhaust damaged
- •ECU heater-control fault
First checks
- •Check heater fuse and power supply
- •Inspect wiring close to the exhaust
- •Measure heater resistance and command behavior
Important
Heater faults can be wiring or fuse issues; do not assume the sensor is the only failed part.
A fault code identifies a detected condition, not a failed part. Confirm manufacturer-specific subcodes and live data.
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