What does it mean?
P1271 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: A/F Sensor-11 (Bank 1 Sensor 1) Circuit Malfunction .
Symptoms
- The MIL is on with the fuel system running in open loop
- Higher fuel consumption and a sulphur or fuel smell from the exhaust
- Rough idle, hesitation and reduced power
- Slow warm up of the sensor so the fault sets shortly after every start
- Failed emissions test and possible black smoke
- The sensor readings on live data stay flat or read a fixed value
Likely causes
- Blown fuse or failed relay supplying the sensor heater circuit
- Open, shorted or chafed sensor wiring where it runs close to the exhaust
- Corroded or melted connector at the sensor pigtail
- Sensor heater element open or drawing excessive current
- Internal failure of the air fuel ratio sensor element after long service or silicone contamination
- Exhaust leak upstream of the sensor cooling it and upsetting readings
- Module input circuit fault, considered last
How to fix it
- Look at the sensor signal on live data during warm up; a flat or fixed value supports a circuit fault
- Check the heater fuse and relay first, since a blown fuse is a common and cheap cause
- Inspect the sensor cable and connector for melting, chafing against the exhaust and corrosion
- Measure heater resistance across the heater pins and compare with specification
- Check for supply voltage and a good ground on the heater circuit with the ignition on
- Test the signal wires back to the module for continuity and shorts, and check for an exhaust leak ahead of the sensor
- Replace the air fuel ratio sensor when the wiring is proven good, then confirm the signal responds normally during a road test