What does it mean?
P1149 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: O2 Control (Bank 1) Out of Range (Sensor Aging) .
Symptoms
- Malfunction indicator lamp on with fuel consumption creeping upward
- Slight hesitation and a less crisp response than the vehicle used to have
- Uneven idle and occasional light surging at constant speed
- Stronger than normal exhaust odour
- Catalyst and oxygen sensor monitors failing to complete
Likely causes
- Normal ageing of the front oxygen sensor after high mileage, with slow and shallow switching
- Element poisoned by silicone sealant fumes, coolant or excessive oil consumption
- Exhaust leak upstream of the sensor letting fresh air reach the element
- Vacuum leak or unmetered air keeping the control loop pinned at one limit
- Fuel pressure outside specification, forcing continuous correction in one direction
- Mass air flow sensor drifted, so the base fuel calculation is already wrong
- Weak sensor heater keeping the element too cool during idle and low load driving
How to fix it
- Graph the front sensor signal at a steady 2500 rpm and count how many times it crosses mid range each second
- Check long term fuel trim values at idle and under load to see which way the control loop is pushed
- Smoke test the intake and inspect the exhaust manifold and gaskets for leaks
- Compare mass air flow readings against the expected value for the engine at idle and at raised speed
- Verify fuel pressure and injector condition before replacing sensors
- Check heater supply and heater resistance on the front sensor
- Replace the aged front sensor with the correct part, then reset adaptations and confirm the switching rate returns to normal