P1135
Air/Fuel Sensor Heater Circuit Response – Bank 1, Sensor 1
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The P1135 code on Toyota vehicles indicates that the heater circuit inside the air/fuel ratio sensor on Bank 1, Sensor 1 is not responding correctly. Every modern oxygen or A/F sensor has a built-in electric heater that brings the sensor up to operating temperature quickly after a cold start. When this heater fails, the sensor takes much longer to start providing accurate readings, causing the engine to run in open-loop mode longer than intended.
During open-loop operation, the engine uses pre-programmed fuel maps instead of real-time sensor feedback, which typically results in a richer fuel mixture. This means worse fuel economy and higher emissions, especially on short trips where the engine never fully warms up. The heater element is the most commonly failed component, though wiring damage from exhaust heat is also common.
This code should be addressed within a week. The fix is usually straightforward — replacing the A/F sensor resolves both the heater issue and any sensor degradation. Before replacing the sensor, check the heater fuse and inspect the wiring connector for heat damage or corrosion, as these are quick, low-cost checks that might save you money.
Severity
Symptoms
- •Check Engine Light illuminated
- •Poor fuel economy, especially on short trips
- •Engine runs rough during cold starts
- •Longer warm-up period before engine runs smoothly
- •Slight hesitation during initial acceleration
- •May notice a sulfur or rotten egg smell from the exhaust
Likely Causes
The internal heater element inside the Bank 1 Sensor 1 A/F sensor burns out over time, preventing the sensor from reaching operating temperature quickly. This is the most common cause.
The entire sensor unit can fail, including the heater circuit. Sensors degrade from heat cycling and contamination over 80,000–120,000 miles.
Broken, corroded, or melted wiring to the sensor heater element can interrupt the circuit. The high-heat environment near the exhaust manifold accelerates wire degradation.
The fuse or relay that powers the oxygen sensor heaters can blow, cutting power to the heater element. This is a quick and inexpensive check.
In rare cases, the ECM itself may fail to supply the proper control signal to the heater circuit, though this is uncommon.
Estimated Cost
Professional Repair
Includes parts + labor
Common Fixes
- Replace the Bank 1 Sensor 1 air/fuel ratio sensor
- Inspect and repair wiring and connectors at the A/F sensor
- Check and replace the oxygen sensor heater fuse
- Clean sensor connector terminals of corrosion