Failed heater element inside the bank 1 sensor 2 air/fuel ratio sensor; Open or shorted wiring in the sensor heater circuit, often near the exhaust or connector; Corroded or damaged sensor connector pins causing high resistance; Blown fuse or faulty relay supplying power to the sensor heater circuit; Engine control module (ECM) driver circuit fault, though this is less common; Exhaust leaks or physical damage to the sensor body or wiring from road debris

DTC codes / Toyota codes / P1155

P1155 · ToyotaAir/Fuel Sensor Heater Circuit Bank 1 Sensor 2

Q: What does code P1155 mean?

Air/Fuel Sensor Heater Circuit Bank 1 Sensor 2. P1155 on Toyota vehicles means the engine computer has detected a problem with the heater circuit inside the bank 1 sensor 2 air/fuel ratio sensor, which is the downstream sensor mounted after the catalytic converter. The heater element is not drawing the current the computer expects, so the sensor cannot reach operating temperature quickly enough for accurate feedback.

P1155 on Toyota vehicles means the engine computer has detected a problem with the heater circuit inside the bank 1 sensor 2 air/fuel ratio sensor, which is the downstream sensor mounted after the catalytic converter. The heater element is not drawing the current the computer expects, so the sensor cannot reach operating temperature quickly enough for accurate feedback.

SystemPowertrain

Code typeToyota specific

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Check engine light illuminated, often with no other symptoms besides the warning light
Slightly higher fuel consumption because the sensor stays in open-loop longer than normal
A pending or stored P1155 code that returns after clearing
Occasional rough idle or hesitation when the engine is cold
In some cases, a related air/fuel sensor heater code for the same sensor may also set

Common causes, most likely first

Failed heater element inside the bank 1 sensor 2 air/fuel ratio sensor
Open or shorted wiring in the sensor heater circuit, often near the exhaust or connector
Corroded or damaged sensor connector pins causing high resistance
Blown fuse or faulty relay supplying power to the sensor heater circuit
Engine control module (ECM) driver circuit fault, though this is less common
Exhaust leaks or physical damage to the sensor body or wiring from road debris

How to diagnose and fix it

Inspect the bank 1 sensor 2 air/fuel sensor connector and wiring for corrosion, chafing, or damage, and repair as needed
Check the heater circuit fuse and relay, and replace any blown fuse or faulty relay
Measure the resistance of the sensor heater element with a multimeter and compare to Toyota specifications; replace the sensor if out of range
Check for battery voltage and ground at the sensor heater connector with the key on, and trace any open or short circuits
If wiring and sensor are good, test the heater control signal from the ECM and inspect for a faulty driver circuit
Clear the code and perform a test drive to confirm the heater circuit operates correctly and the code does not return

Downstream sensor heater faults on Toyotas

A P1155 code does not always mean the sensor itself has failed; a corroded connector or a rubbed-through wire near the exhaust is a frequent cause that technicians overlook.
Toyota air/fuel ratio sensors are heated to reach operating temperature quickly, and a weak heater can cause lazy response without setting a heater code until resistance drifts far enough out of range.
Replacing the sensor without checking the heater circuit fuse and relay can lead to a repeat failure if the root cause is electrical rather than the sensor element.
On some Toyota models, a P1155 may be stored alongside other air/fuel sensor codes, so diagnosing the entire circuit rather than just the sensor is essential.
The downstream sensor heater circuit is often powered through a fuse shared with other components, so a blown fuse may cause multiple codes and should be checked first.

Can I keep driving with P1155?

You can usually continue driving with P1155, but avoid long periods of idling or heavy load until the fault is repaired, because the sensor may not reach operating temperature and fuel economy can suffer. Have the circuit inspected soon to prevent catalytic converter damage from prolonged rich running.

Tools that help

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Guidance is general and written for Toyota vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.