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P1135 Toyota — A/F Sensor Heater Circuit Malfunction — Bank 1 Sensor 1

Moderate

Quick answer

P1135 means the heater circuit inside the upstream air/fuel ratio sensor on bank 1 has failed — a Toyota/Lexus-specific code, classic on the Camry, Avalon, Sienna, RAV4 and RX of the late-90s/2000s. The sensor itself is the usual fix, but check the heater fuse and connector first; a genuine Denso replacement matters here.

What it means

Toyota’s air/fuel ratio (A/F) sensor is a wideband evolution of the oxygen sensor: instead of just rich/lean, it reports exactly how rich or lean the exhaust is, and the computer trims fuel from its signal continuously. To read accurately it must be hot — far hotter than exhaust alone provides at idle or right after start-up — so a heater element lives inside the sensor and the ECM drives it. P1135 sets when the ECM sees the wrong current through that heater circuit on bank 1 — the side of the engine containing cylinder 1, usually the rear (firewall) bank on Toyota’s transverse V6s, or simply the only bank on a four-cylinder. Sensor 1 is the upstream sensor, before the catalytic converter.

This is one of the most familiar Toyota-specific codes in existence: the heater element simply burns out with age, and entire generations of Camrys, Siennas, Highlanders and Lexus RX 300s have logged it. The failure is almost always inside the sensor, but the circuit includes a fuse and a connector, and those are free to check — which is why they come first.

One useful tell: if P1135 and P1155 set together on a V6, two sensors almost certainly didn’t die the same day — suspect the shared fuse or a wiring problem feeding both heaters instead.

P1135 symptoms: what you'll notice

  • Often nothing but the check engine light — with the heater dead the sensor still works once exhaust heat warms it, so the engine usually drives normally.
  • Slightly worse fuel economy, because the computer runs a conservative fixed fuel map until the sensor reports ready — longest on short trips and cold mornings.
  • A failed emissions/smog inspection: the code keeps the oxygen-sensor readiness monitor from completing.
  • Occasionally slightly rough running for the first minutes after a cold start.

Common causes

Ordered from most to least likely.

  1. 1.

    Burned-out heater element inside the A/F sensor

    The overwhelmingly common cause — heaters fail from age and heat cycles.

  2. 2.

    Blown heater fuse (often labeled A/F or EFI in the engine-bay box)

    Free to check, and the prime suspect when both banks set heater codes together.

  3. 3.

    Damaged connector or wiring to the sensor

    The harness lives near hot exhaust — look for chafed or heat-hardened insulation and green-crusted pins.

  4. 4.

    Failed ECM heater driver

    Rare — only on the table after the sensor, fuse, and wiring all measure good.

How to fix it: diagnosis, step by step

Cheapest and most likely checks first.

  1. 1 Check the fuses first

    Find the fuse box diagram (lid or owner’s manual) and check the fuse feeding the A/F sensor heaters. A blown fuse with heater codes on both banks is practically a diagnosis in itself — but ask why it blew before just replacing it.

  2. 2 Inspect the sensor connector

    Unplug the bank 1 upstream sensor and look for melted plastic, corrosion, or pins pushed out of the housing. The connector usually clips to a bracket above the exhaust — heat damage is common real estate here.

  3. 3 Measure the heater resistance

    With the sensor unplugged, measure resistance across the heater pins (your model’s manual identifies them; on most Toyota A/F sensors spec is in the low single-digit ohms at room temperature). Open circuit (infinite reading) confirms the heater is burned out — replace the sensor.

  4. 4 Verify power and ground at the harness

    If the heater measures fine, check the harness side: battery voltage on the supply pin with the key on, and a good ECM-side ground path. Voltage present + good sensor = chase the wiring between connector and ECM.

  5. 5 Replace with the right part

    Buy a Denso sensor (Toyota’s original supplier) for your exact model and engine. Universal or bargain A/F sensors are a famous source of comeback codes on Toyotas — this is the wrong place to save twenty dollars. Anti-seize on the threads, and snug — not gorilla — torque.

Parts & tools you may need

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Related codes

Frequently asked questions

What does code P1135 mean?
P1135 means the heater circuit inside the upstream air/fuel ratio sensor on bank 1 has failed — a Toyota/Lexus-specific code, classic on the Camry, Avalon, Sienna, RAV4 and RX of the late-90s/2000s. It’s moderately serious — you can usually keep driving gently, but diagnose it soon.
Can I drive with P1135?
Yes — the engine runs fine on the warmed-up sensor and the conservative cold map. The real costs are a little fuel economy, an emissions test you can’t pass, and a check engine light that will mask any new problem that appears behind it. Fix it soon, not frantically.
Is the A/F sensor the same as an oxygen sensor?
It’s the same job done with more precision: a wideband sensor that reports exactly how rich or lean the mixture is rather than just which side of ideal it’s on. It looks like an O2 sensor and lives in the same place, but it costs more and is not interchangeable with a conventional sensor — order by your exact model.
Why do P1135 and P1155 appear together?
Because both heaters share a fuse and supply circuit on Toyota’s V6s. Two sensors rarely fail simultaneously; one fuse does it all the time. Check the fuse box before pricing two sensors.
Why does the brand of replacement sensor matter so much?
Toyota ECMs are calibrated around Denso’s sensor characteristics. Bargain and universal sensors frequently read slightly off or fail the heater monitor again within months — the forums are full of twice-bought sensors. Denso first time is the cheap path.
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