What does it mean?
This code applies the lean to rich response test to the third sensor in the bank 2 exhaust stream. The module briefly enriches the mixture and measures how long the sensor takes to swing from a lean indication to a rich one, and it stores the code when that time exceeds the calibrated maximum. A sensor that is slow in this direction has usually lost element activity or is covered with deposits, so extra fuel has to reach it before the voltage will rise. Because the same test also runs on bank 1, the healthy side gives a useful reference for how quickly the transition should happen.
Symptoms
- MIL on with normal driveability in most conditions
- Gradual increase in fuel consumption
- Emissions readiness monitors that will not complete
- Slight hesitation when the throttle is opened sharply
- Further catalyst or oxygen sensor codes appearing on the same bank over time
- Failed emissions inspection without a customer complaint about how the vehicle runs
Likely causes
- Sensor element worn out and no longer switching quickly at high mileage
- Carbon, oil ash or fuel additive residue coating the sensing surface
- Silicone or sealant poisoning from an unsuitable product used during a repair
- Exhaust leak on bank 2 ahead of the sensor diluting the gas and delaying the rich transition
- Heater circuit weak or intermittent so the element runs cool
- Resistance in the signal or ground wiring slowing the measured response
- An earlier period of heavy rich running or oil burning that fouled the element
How to fix it
- Graph the bank 2 sensor 3 signal during a snap throttle event and compare the lean to rich time with the same sensor position on bank 1
- Use the freeze frame to reproduce the load and temperature at which the test ran
- Inspect the bank 2 exhaust ahead of the sensor for leaks at flanges, clamps and welds
- Verify heater supply, ground and resistance and check how quickly the sensor becomes active from a cold start
- Look for oil consumption, coolant loss or an unsuitable sealant that could have contaminated the element
- Check the signal and ground circuits for voltage drop and inspect the connector for corrosion
- Fit a correct specification sensor once the wiring and exhaust are proven, then confirm the faster response on a graph