What does it mean?
This code covers the same sensor as its rich to lean counterpart, the third sensor in the bank 1 exhaust stream, but it judges the other direction of travel. During the response test the module adds fuel and measures how long the sensor takes to move from a lean indication to a rich one. It stores the code when that transition is slower than the calibrated limit. A lazy lean to rich response is typical of an element that has lost activity or is coated with deposits, since it needs excess fuel to reach the element before the voltage can rise.
Symptoms
- MIL on with little or no change in how the vehicle drives
- Slightly higher fuel consumption over time
- Readiness monitors that will not complete before an emissions test
- Occasional hesitation when the throttle is opened quickly
- Additional oxygen sensor or catalyst codes appearing later
- Emissions test failure without an obvious driveability fault
Likely causes
- Aged sensor element that has lost catalytic activity with mileage
- Deposits of carbon, oil ash or fuel additive residue coating the sensing surface
- Silicone or sealant contamination from an unsuitable product used in the exhaust or engine
- Exhaust leak ahead of the sensor diluting the gas and delaying the rich signal
- Heater circuit weak or intermittent, so the sensor operates below its ideal temperature
- High resistance in the signal or ground wiring slowing the measured response
- A previous long term rich or oil burning condition that fouled the element
How to fix it
- Graph the sensor signal during a snap throttle event and compare the lean to rich transition time against the other sensors on the vehicle
- Review the freeze frame to reproduce the load and temperature conditions of the test on a road test
- Inspect the exhaust ahead of the sensor for leaks, using a smoke test where access is difficult
- Check heater supply, ground and resistance, and confirm the sensor reaches operating temperature quickly
- Investigate any oil consumption or coolant loss that could have contaminated the element
- Measure voltage drop on the signal and ground circuits and inspect the connector for corrosion and water
- Replace the sensor with the correct part after the wiring and exhaust are proven, then confirm the improved response with a graph