Fault code P1155 – a step-by-step guide to diagnosing and fixing it

The meaning of error code P1155 – Alternative Fuel Controller

P1155: Causes, signs and repairs

Error code P1155 is displayed and the check engine light is on - what does this mean?

The OBD/EOBD system has detected a fault in the air/fuel ratio sensor (A/F sensor) of bank 2, sensor 1. This DTC P1155 occurs mainly in Toyota, Lexus and some other Asian manufacturers and indicates that the sensor is not responding properly to changes in the air-fuel mixture.

What can cause this error code?

Defective air-fuel ratio sensor bank 2, sensor 1
Damaged or corroded cable connections to the A/F sensor
Loose or dirty plug connections
Defective heating of the A/F sensor
Short circuit or interruption in the sensor wiring
Defective engine control unit (ECU)
Vacuum leak in the intake tract
Dirty or clogged air filter

What symptoms occur in parallel with fault code P1155?

Poor fuel efficiency: Increased fuel consumption due to incorrect air/fuel mixture
Unsteady idling: Engine runs irregularly at idle speed
Power loss: Reduced engine power, especially during acceleration
Exhaust problems: Increased emission values and exhaust odor
Starting problems: Difficulty starting the engine when cold
Check engine light: Permanent display of the check engine light

How can I fix the problem with fault code P1155?

Repairing fault code P1155 requires a systematic diagnosis and appropriate measures.
Replacing the defective A/F sensor: Replace the air/fuel ratio sensor bank 2, sensor 1 completely, as this is the most common cause of the trouble code
Repair the sensor wiring: Check all cables and plug connections to the A/F sensor, repair or replace damaged cables
Cleaning the plug connections: Remove corrosion and dirt from all electrical connections and treat with contact spray
Repairing vacuum leaks: Check intake tract for leaks and replace defective hoses or seals
Replacing the air filter: Replace clogged or dirty air filter to ensure proper air supply
ECU reset and reprogramming: Reset the engine control unit and carry out a software update if necessary

FAQ - Frequently asked questions about DTC P1155

Can I continue driving with error code P1155?

It is possible to drive for a short time, but you should have the problem rectified as soon as possible. The defective A/F sensor can lead to increased fuel consumption and engine damage.

How much does it cost to repair error code P1155?

The costs vary between 150-400 euros, depending on whether only the sensor or additional wiring needs to be replaced. In the case of workshop work, labor costs of 80-120 euros are added.

How do I recognize a defective A/F sensor with code P1155?

Typical signs are rough idling, increased fuel consumption and an illuminated engine control light. An OBD diagnosis clearly confirms the fault code.

Can I repair the P1155 error code myself?

Replacing the A/F sensor is feasible for experienced hobby mechanics, but a specialist workshop is recommended as the precise diagnosis requires special equipment.

How long does a new A/F sensor last after P1155 repair?

A high-quality air-fuel ratio sensor will normally last 100,000-150,000 kilometers, depending on driving style and maintenance.

Why does the EOBD code P1155 keep recurring?

Recurring P1155 codes usually indicate undetected wiring problems, vacuum leaks or a faulty engine control unit that require additional repair.

Vehicles in which fault code P1155 occurs most frequently

Error code P1155 is a manufacturer-specific DTC that occurs mainly in Toyota and Lexus vehicles and indicates problems with the air-fuel ratio sensor, but is most common in the following vehicles:

Toyota: Camry, Corolla, RAV4, Highlander, Sienna, Avalon (2001-2015)
Lexus: ES300, ES330, RX300, RX330, GS300, LS400 (2001-2012)
Scion: tC, xB, xA (2004-2010)
Mazda: Tribute, MPV (2001-2008)
Subaru: Legacy, Outback, Forester (2003-2009)
Mitsubishi: Outlander, Eclipse (2003-2012)

If the code P1155 occurs in your vehicle, you should first have a full OBD diagnosis carried out to identify the exact cause. As this trouble code mainly affects the A/F sensor, a prompt repair is important to prevent consequential damage to the engine and restore optimum fuel efficiency.

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