What does it mean?
P1103 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: O2 Sensor Circuit (Bank 1-Sensor 1) Output Too Low .
Symptoms
- Check engine light on with lean fuel trim values stored in the freeze frame
- Poor fuel economy and a rough or hunting idle
- Hesitation and a flat spot when accelerating from low speed
- Engine slow to settle after a cold start
- Emissions test failure and, in some cases, a sulphur-like smell from the exhaust
- Occasional misfire codes if the mixture is genuinely lean
Likely causes
- Exhaust leak ahead of or close to the sensor drawing fresh air into the stream and holding the reading low
- Aged or contaminated sensor element, poisoned by oil, coolant or silicone
- Signal wire shorted to ground or a high-resistance connection in the sensor harness
- Corroded sensor connector, often on the side exposed to road spray
- Genuinely lean running caused by an intake vacuum leak, low fuel pressure or restricted injectors
- Heater circuit fault leaving the sensor too cool to generate a proper signal
- Faulty module input, only after all of the above have been ruled out
How to fix it
- Watch the Bank 1 upstream sensor voltage and both short and long term fuel trims in live data at idle and at raised rpm
- Listen and look for exhaust leaks between the manifold and the sensor; even a small leak upstream will hold the reading low
- Smoke test the intake tract for vacuum leaks and check the fuel pressure against the specification
- Inspect the sensor connector for corrosion, melted insulation and heat damage from the exhaust
- Check the heater circuit for supply voltage and measure the heater element resistance
- Introduce a controlled rich condition and watch whether the sensor responds; a lazy or flat response condemns the sensor
- Replace the sensor once leaks and fuelling faults are ruled out, then re-check fuel trims after a drive cycle