What P0135 means
Oxygen sensors only read accurately hot, so each contains an electric heater to reach operating temperature in seconds rather than minutes. P0135 means the upstream Bank 1 sensor's heater circuit has failed — the sensor still works once exhaust heat warms it, but every cold start runs blind for a while.
What you’ll notice
- Check engine light
- Slightly worse economy on short trips
- No other symptoms in most cases
Likely causes and repair cost
Broad US independent-shop bands, parts and labour.
Can you drive with P0135?
Yes — the practical penalty is a few minutes of imprecise fuelling after each cold start. Short-trip city drivers pay the most; fix it before your emissions test regardless.
The misdiagnosis to avoid
Skipping the fuse. Heater circuits are fused, sensor replacement is a few hundred dollars, and the fuse is under a dollar — yet the sensor routinely gets replaced first. Thirty seconds at the fuse box is the correct opening move on any heater-circuit code.
Describe what it’s doing in your own words and the symptom checker gives you a safe-to-drive verdict, ranked causes with costs, and notes to take to the shop — free, no sign-up.
Read the code yourself
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Check price on AmazonQuestions people ask
Why does the heater matter if exhaust heat works too?
Time. Exhaust heat takes minutes; the heater takes seconds — and those minutes are exactly when the engine runs its richest, dirtiest mixture. Regulations required fast closed-loop control, hence the heater. Its failure mostly costs you on short trips that end before free heat arrives.
Same code came back after a new sensor — why?
Then the sensor was never the fault: the heater's supply is dead — fuse, relay, or wiring. The new sensor's heater is sitting unpowered just like the old one's. This is the textbook case for testing the circuit before (or at least after) the first parts swap.