Affected Component: Air/Fuel Sensor Heater Circuit Bank 2 Sensor 1
System: Engine / Emissions / Control
Severity: Moderate – May affect drivability or emissions
🔍 What Does Toyota Error Code P1155 Mean?
P1155 – Air/Fuel Sensor Heater Circuit Bank 2 Sensor 1 occurs when the ECM detects an abnormal current or response from the A/F sensor heater circuit on bank 2. This sensor is critical for maintaining the correct air-fuel ratio, especially during cold starts.
📍 When and Why It Appears
- The heater circuit resistance is out of range
- The A/F sensor is faulty or slow to respond
- The wiring or connector to the sensor is open or shorted
- ECM detects improper voltage to the heater circuit
⚠️ Common Symptoms of P1155
- Check Engine Light ON
- Increased fuel consumption
- Hesitation or poor throttle response
- Failed emissions test
🔎 Possible Causes
- Failed A/F sensor (Bank 2 Sensor 1)
- Open or short in sensor wiring harness
- ECM malfunction (rare)
- Contaminated sensor tip (fuel additives, silicone)
🧰 How to Diagnose P1155
- Scan for DTCs and review freeze frame data
- Measure resistance across sensor heater terminals
- Check voltage supply to heater circuit (should be around 12V)
- Inspect wiring for breaks or corrosion
- Compare A/F sensor response with Bank 1 (if available)
🔧 How to Fix Toyota Error Code P1155
- Replace the A/F sensor on Bank 2 Sensor 1 with OEM spec
- Repair damaged wiring or connector terminals
- Check ECM and fuses for power/ground integrity
- Clear codes and retest using live data for proper heater activation
💰 Estimated Repair Cost
- A/F Sensor Replacement: ₱2,500 – ₱6,000
- Wiring Repair: ₱800 – ₱2,000
- Diagnostics and Labor: ₱1,000 – ₱2,000
🧠 Expert Tips
- Only use Denso or OEM-specified A/F sensors
- After replacing, drive at various speeds to allow ECM relearning
- Don’t confuse O2 and A/F sensors — they function differently