P1133 Code: Air Fuel Ratio Sensor Circuit Slow Response (Toyota, Bank 1 Sensor 1)

What the P1133 code means

P1133 is a manufacturer-specific code: the 1 in the second position means each automaker defines what it stands for, not the generic standard. That is why the same number means different things depending on the vehicle, as the table below shows. This page covers the Toyota and Lexus meaning.

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 P1133 code when the A/F sensor reacts too slowly to mixture changes on bank 1. Exhaust leaks ahead of the sensor and aging sensors are the most common causes.

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.

P1133 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 P1133 code

1. Aged or contaminated A/F sensor, fouled by oil or coolant.
2. Exhaust leak ahead of the sensor. Outside air skews the reading.
3. A mixture that really is wrong, from vacuum leaks or injectors.
4. Connector or wiring damaged by exhaust heat.

How to diagnose the P1133 code step by step

1. Watch the sensor signal on the scan tool. It should change quickly when you accelerate (rich) and when you let off (lean).
2. Check the fuel trims to rule out a mixture that really is wrong.
3. Look for exhaust leaks ahead of the sensor.
4. Inspect the sensor. White or black deposits point to contamination.

How to fix the P1133 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 P1133 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 P1133