What does it mean?
This is the bank 2 version of the rich to lean response test, applied to the third sensor in that bank's exhaust stream, downstream of the additional catalyst section. During a controlled fuel test the module drives the mixture lean and measures how quickly the sensor voltage drops to reflect it. The code is stored when that transition takes longer than the calibrated maximum. Since the same test usually runs on both banks, comparing the two sides is one of the quickest ways to see how far the bank 2 sensor has slowed down.
Symptoms
- MIL on while the engine still runs and drives normally
- Small but steady rise in fuel consumption
- Readiness monitors that do not complete, which prevents an emissions test
- Occasional light hesitation during throttle transitions
- Catalyst or additional oxygen sensor codes appearing over time on the same bank
- Emissions test failure with no clear driveability symptom
Likely causes
- Sensor element aged so that its switching speed has fallen with mileage
- Sensing tip coated with oil, coolant residue or silicone from an unsuitable sealant
- Exhaust leak on the bank 2 side ahead of the sensor letting outside air distort the reading
- Weak or intermittent heater circuit keeping the element below its ideal temperature
- Carbon and soot deposits after a long period of rich running on that bank
- Signal or ground circuit resistance slowing the response the module measures
- Sensor not tightened correctly in its bung so the tip is poorly exposed to the gas flow
How to fix it
- Graph the bank 2 sensor 3 signal during a lift off and reopen event and compare it directly with the equivalent bank 1 sensor
- Read the freeze frame for the conditions of the test, then reproduce them on a road test
- Inspect the bank 2 exhaust for leaks at the manifold, flanges and clamps ahead of the sensor
- Check the heater circuit for supply, ground and correct resistance, and time how quickly the sensor becomes active
- Investigate any cause of contamination such as oil consumption or coolant entering the exhaust on that bank
- Measure voltage drop on the signal and ground circuits and inspect the connector for water and corrosion
- Replace the sensor with a correct specification unit once the wiring and exhaust are proven, then verify the response with a new graph