What does it mean?
P1155 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: HO2S Heater Circuit Current Malfunction .
Symptoms
- Malfunction indicator lamp on within a few minutes of a cold start
- Extended open loop operation and poor fuel economy while the engine warms
- Slightly rough running until the sensor comes up to temperature
- Sensor heater fuse showing signs of heat or failing occasionally
- Emissions readiness monitors staying incomplete
Likely causes
- Failing relay or a heater supply that drops out under load
- Corroded or loose terminal at the fuse box feeding the heater circuit
- High resistance splice or a stretched crimp in the heater feed wire
- Heater element resistance drifted upward with age, reducing current draw
- Loose or corroded body ground for the heater return path
- Intermittent open in the pigtail where it flexes near the exhaust
- Low system voltage caused by a weak battery or a charging fault
How to fix it
- Measure system voltage at the battery and confirm the charging system is working before circuit testing
- Check the heater fuse and its holder for heat damage, then confirm voltage on both sides with the key on
- Measure voltage at the sensor connector with the heater energised, so the circuit is tested under load
- Perform voltage drop tests along the feed wire and along the ground return
- Compare heater resistance across the element pins against the specified value
- Wiggle the pigtail during the measurements to expose an intermittent open
- Repair the supply, splice or ground fault first, and replace the sensor only if its element is out of specification