P0135: O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)
The heater inside the front oxygen sensor on bank 1 is not working.
Severity: 1 of 4
Generally safe to drive. You may notice worse fuel economy after cold starts. Fix it soon to keep emissions and fuel control normal.
Estimate range covers the repairs listed below; see the cost breakdown. A flashing check engine light, a hot temperature gauge, or brakes that feel different mean stop driving and get help.
What P0135 means
Oxygen sensors only work when hot. They contain a small electric heater so they start reporting quickly after a cold start. P0135 means the computer sees a problem in that heater circuit for the upstream sensor on bank 1.
Sensor 1 is the sensor before the catalytic converter.
Common causes (cheapest likely first)
- Failed heater in the oxygen sensor. The most common cause.
- Blown fuse for the heater circuit. Check the fuse first; it is cheap.
- Damaged wiring or connector. Exhaust heat can melt wiring.
Symptoms
- Check engine light
- Slightly worse fuel economy
- Possible failed emissions test
DIY difficulty: Easy to moderate
Front sensors are often reachable from the top of the engine. A seized sensor may need heat and a proper socket.
Tools: OBD-II scanner, Oxygen sensor socket, Multimeter, Anti seize
Estimated repair cost
This is an estimate, built from typical parts price ranges plus labor hours times an assumed shop rate of $110 to $190 per hour. Actual prices vary by vehicle, region, and shop. Diagnosis fees are often extra.
| Repair | Parts | Labor | Estimate (low / high) |
|---|---|---|---|
| Front oxygen sensor | $40 to $160 | 0.3 to 1.0 h | $40 + 0.3 × $110 = $73 $160 + 1.0 × $190 = $350 |
| Wiring repair | $5 to $40 | 0.5 to 1.5 h | $5 + 0.5 × $110 = $60 $40 + 1.5 × $190 = $325 |
Watch a repair video
Search YouTube for “P0135 fix” videos. Pick a recent video that matches your engine, and confirm the diagnosis before buying parts.
By make
This code works the same way on every make. See brand notes.
Repair manuals
Step-by-step service manuals with torque specs and wiring diagrams:
Haynes manuals Chilton manuals
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Related codes
Check for recalls
Before paying for a repair, enter your VIN in the NHTSA recall lookup. Emissions parts may also be covered by a federal emissions warranty; check your warranty booklet.
FAQ
Do I need the brand name sensor?
A quality sensor matching your part number is fine. Very cheap sensors sometimes cause new codes.
Can I test the heater myself?
Yes, with a multimeter you can measure heater resistance and compare to the service manual specification.