P1155
Air/Fuel Sensor Heater Circuit Response – Bank 2, Sensor 1
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The P1155 code on Toyota vehicles is the Bank 2 equivalent of P1135. It indicates that the heater circuit in the air/fuel ratio sensor on Bank 2, Sensor 1 is not functioning properly. The heater's job is to bring the sensor up to its operating temperature (around 1,200°F) as quickly as possible after a cold start so the ECM can switch from open-loop to closed-loop fuel control.
When this heater fails, the sensor relies on exhaust heat alone to warm up, which takes significantly longer. During this extended warm-up period, the engine runs on preset fuel maps that tend to be richer than optimal, wasting fuel and increasing emissions. This is why the impact is most noticeable on short trips where the engine may never fully reach operating temperature.
P1155 often appears alongside P1135, since the same fuse or conditions can affect both banks' sensor heaters. If you see both codes, check the shared heater fuse first — it's a $2 fix. If the fuse is fine, plan to replace the sensor. The Bank 2 sensor can sometimes be harder to access than Bank 1, but it's still a manageable DIY job with basic tools and a sensor socket.
Severity
Symptoms
- •Check Engine Light illuminated
- •Reduced fuel economy on short drives
- •Rough cold start idle
- •Engine takes longer to warm up and run smoothly
- •Mild hesitation during the first few minutes of driving
- •Possible increase in exhaust emissions
Likely Causes
The internal heater in the Bank 2, Sensor 1 A/F sensor has burned out, preventing the sensor from reaching its operating temperature quickly after engine start.
The complete sensor unit on Bank 2 has worn out from extended heat cycling and mileage, affecting both the sensing element and heater.
The wiring harness near the exhaust manifold on Bank 2 is prone to heat damage, and connectors can corrode over time, interrupting the heater circuit.
A failed fuse supplying power to the oxygen sensor heater circuits can disable the heater. This fuse often powers both Bank 1 and Bank 2 heaters.
Rarely, the ECM's driver circuit for the heater relay may fail, though this is the least likely cause.
Estimated Cost
Professional Repair
Includes parts + labor
Common Fixes
- Replace the Bank 2 Sensor 1 air/fuel ratio sensor
- Repair or replace heat-damaged wiring near the exhaust manifold
- Check and replace the oxygen sensor heater fuse
- Clean corroded sensor connector pins