P1155 Code: Air Fuel Ratio Sensor Heater Circuit (Toyota, Bank 2 Sensor 1)

What the P1155 code means

P1155 is a manufacturer-specific code: the 1 in the second position means each automaker defines what it stands for, not the generic standard. The most widespread definition is the one used by Toyota and Lexus. If your vehicle is another brand, confirm the code text with a scan tool that supports that manufacturer.

Toyotas with an air fuel ratio sensor (A/F sensor) use it ahead of the catalytic converter in place of the classic oxygen sensor. It measures the mixture across the whole range, and the computer shows it as a current or as a lambda ratio. To work, it has to be very hot, which is why it has an internal heater.

The computer sets the P1155 code when the A/F sensor heater does not heat, or its circuit is open or shorted, on bank 2. The heater fails from age or from a blown fuse, and without it the sensor takes a long time to give a signal after startup.

Before you repair anything, confirm the make, model, year and engine. With manufacturer codes, the same number can change even between engines from the same brand.

P1155 code symptoms

• Check engine light on.
• Higher fuel use.
• Slightly rough idle after a cold start.
• A catalytic converter code (P0420) may show up over time.

Likely causes of the P1155 code

1. Open sensor heater. The most frequent cause.
2. Blown heater fuse (EFI or A/F HTR).
3. Sensor connector damaged by heat.
4. Heater relay on some models.

How to diagnose the P1155 code step by step

1. Measure the heater resistance at the sensor connector.
2. Check the fuse and the power supply. You should see 12 V with the ignition on.
3. Inspect the connector. It often burns from the heat.
4. Clear the code and check whether it returns after a cold start.

How to fix the P1155 code

• Replace the A/F sensor if it fails the tests, and use one to the original specification.
• Repair exhaust leaks or the wiring.
• Clear the P1155 code and complete a drive cycle to confirm the repair.

Technical reference data

• A/F sensor heater resistance: about 1.8 to 3.4 ohms at 20 °C (68 °F).
• Sensor voltage on the scan tool: close to 3.3 V at the ideal mixture on many models (higher means lean, lower means rich).
• P1xxx codes are manufacturer-specific: confirm the definition with a scan tool that supports your brand.
• Values are approximate: check the manufacturer data for your vehicle.

Brand-specific notes

Very common on high-mileage Corolla, Camry, RAV4, Highlander and Sienna models. Cheap generic sensors often cause trouble on these engines.

If your vehicle is another brand, check the table above for the meaning its manufacturer gives the code, and confirm it with a scan tool that supports that brand.

Frequently asked questions about P1155