Number P0135: O2 Sensor Heater Circuit Bank 1 Sensor 1
The upstream oxygen sensor on bank 1 (sensor 1) has an electric heater so that it reaches its working temperature of about 300 °C soon after a cold start. The control module switches the heater on the ground side and checks driver voltage and heater current: GM fails it outside 0.3–2.5 A (or 3.1 A)
Can you drive with P0135?
Severity: Plan the repair. Yes — this is an emissions-system fault. The car will generally drive normally, but it will fail an emissions inspection with the light on.
If you ignore it: Fuel economy and emissions creep up, and some faults in this family (rich/lean running) stress the catalyst over time.
This is the #5 most common code in our top-150 library, in the oxygen & exhaust sensors family (Powertrain system). Severity is Number Nest's editorial triage — if the light is flashing or the car feels unsafe, stop driving it whatever any page says.
What P0135 means
The upstream oxygen sensor on bank 1 (sensor 1) has an electric heater so that it reaches its working temperature of about 300 °C soon after a cold start. The control module switches the heater on the ground side and checks driver voltage and heater current: GM fails it outside 0.3–2.5 A (or 3.1 A) and calls it 'heater performance', Ford outside roughly 0.22–0.465 A minimum to 3 A, Saab Trionic outside 0.5–2.3 A for 5 s. Manufacturers split heater faults differently between P0030–P0032, P0053 and P0135. With the heater dead, closed-loop control starts late after a cold start. If P0135 and P0141 appear together, check the shared fuse.
Systems involved: oxygen sensor heater bank1 sensor1, oxygen sensor heater circuit, fuses.
Causes, ranked by likelihood
| # | Cause | Likelihood |
|---|---|---|
| 1 | Heater element of the sensor burnt out (sensor must be replaced) | most likely |
| 2 | Fuse or relay of the heater supply faulty | possible |
| 3 | Heater wiring or connector open, corroded or shorted | possible |
| 4 | Unsuitable replacement sensor (different heater resistance) | less common |
| 5 | Heater driver in the control module faulty | less common |
Check them in order — the list is ranked so the likely, cheaper causes come before the expensive part.
Symptoms you may notice
- Check engine light on
- Longer cold-start phase without mixture control, more fuel and emissions
- Follow-up codes P0133/P0134 possible (cold sensor)
Misdiagnosis traps
- A blown heater fuse or a chafed heater wire sets this code on a healthy sensor — check the fuse and circuit before the part.
- On some cars the heater driver lives in the PCM; a shorted sensor heater can take the driver with it. Test, don't assume.
How a good shop confirms it
- Test heater resistance and power/ground at the connector; inspect the harness where it passes near the exhaust.
Repair options & costs
| Repair | Shop total (parts + labor) | DIY (parts only) | Difficulty |
|---|---|---|---|
| Oxygen sensor — upstream (pre-cat) | $143 – $390 | $80 – $240 (parts only) | 2/5 |
National ranges from Number Nest's cost model (midsize car, independent shop, US-average labor). Published cross-check — Oxygen sensor — upstream (pre-cat): CarMD 2026 national average $287.
OBDex repair data for this code rates the job difficulty easy with a typical labor time in the 0.2–1.5 hour range and DIY possible: yes.
Price this repair in your state
Estimated total: — (midsize car, independent shop)
Check the federal emissions warranty first
Before you pay: federal law (the Clean Air Act emissions warranty) requires the manufacturer to cover the catalytic converter and the engine computer (PCM) for 8 years or 80,000 miles on 1995-and-newer cars, whichever comes first. California-emissions (CARB) states cover a longer list of parts for 7 years/70,000 miles, and PZEV-rated vehicles sold in CARB states carry 15-year/150,000-mile emissions coverage on many components. Check your warranty booklet or a dealer lookup before authorizing this repair out of pocket.
Frequently asked questions
Does the heater circuit affect how the car runs?
Mainly the first minutes: an unheated sensor delays closed-loop fueling, costing a little fuel and emissions on cold starts. The sensor itself usually still works once exhaust heat takes over.
How much does it cost to fix P0135?
The fix most associated with this code — oxygen sensor — upstream (pre-cat) — runs $143 – $390 at an independent shop for a midsize car in our cost model (parts + labor, US average). The code names a system, not a part, so confirm the cause before spending: the ranked causes above are ordered by likelihood.
Can I drive with P0135?
See the can-you-drive verdict above — it is based on the system involved and the cascading-damage risk, and it is our editorial triage, not a manufacturer instruction. If the light is flashing or the car feels unsafe, stop driving it regardless of any code.
Will P0135 clear itself?
If the fault was a one-off (a loose cap, a cold-start glitch), the light can go out after several clean trips and the code ages into history. A fault that is still present re-sets the code as soon as the car runs that self-test again — monitors run under specific conditions, which is why "it hasn't come back in two days" is not proof of a fix.
Will my car fail inspection with P0135?
In states with OBD-based emissions inspection, yes — an illuminated check-engine light or an incomplete readiness monitor fails the test regardless of what the tailpipe would show. C-codes (ABS) fall under safety inspection instead in states that have one.
What should I check first for P0135?
The first item on the ranked-causes list above — it is ranked likelihood-first for exactly this reason — plus the free checks: recent work in the area (connectors left loose are a classic), fluid levels, and the battery and grounds on electrical codes.
Where this data comes from
Code facts, causes and symptoms come from OBDex — an open dataset of independently authored descriptions of the standardized generic OBD-II codes (CC0 1.0, public domain; github.com/foerbsnavi/OBDex). The SAE J2012 document itself is copyrighted and is not reproduced here. Cost ranges are Number Nest's own US planning model: national parts and labor ranges cross-checked against the CarMD Vehicle Health Index 2026 published averages, with labor adjustable by the BLS OEWS May 2025 state wage index for auto technicians (occupation 49-3023) — a wage index, not a surveyed shop rate. Severity and can-you-drive notes are our editorial triage, not a manufacturer instruction.