What does it mean?
P1133 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: HO2S-11 (Bank 1 Sensor 1) Insufficient Switching .
Symptoms
- Malfunction indicator lamp on with the engine otherwise running acceptably
- Fuel consumption climbing without an obvious cause
- Slightly uneven idle and a mild hesitation on light acceleration
- Exhaust smell that is stronger than usual
- Catalyst monitor never completing, causing an emissions test failure
Likely causes
- Aged, lazy sensor element that has slowed down after long service
- Sensor contamination from coolant, silicone sealant fumes or heavy oil consumption
- Exhaust leak ahead of the sensor letting fresh air in and holding the signal lean
- Small unmetered air leak in the intake or a leaking vacuum line skewing the mixture
- Weak sensor heater keeping the element below its ideal temperature at idle
- Fuel pressure too low or too high, holding the mixture on one side of stoichiometric
- High resistance in the signal or ground circuit damping the sensor's voltage swing
How to fix it
- Graph the Bank 1 Sensor 1 voltage at 2500 rpm; a healthy sensor crosses the mid point several times per second
- Force the mixture rich by adding propane at the intake and then lean by creating a controlled vacuum leak, watching how fast the sensor responds
- Compare short and long term fuel trims on both banks to see whether the mixture itself is off
- Inspect the exhaust manifold, gaskets and pipe joints ahead of the sensor for leaks
- Smoke test the intake for unmetered air, then check fuel pressure against specification
- Measure sensor heater resistance and confirm the heater circuit is live
- Replace the sensor once the fuel, air and exhaust sides are proven correct, then recheck switching speed