Catalyst System Efficiency Below Threshold (Bank 2)
The catalytic converter (the exhaust part that cleans the gases) on bank 2 is not cleaning as much as it should. “Bank 2” is the side of the engine opposite cylinder 1: it only exists on V engines or engines with two cylinder banks, not on inline four-cylinder engines.
What the car has detected
The engine computer compares the oxygen sensor before the catalytic converter with the one after it. With a healthy converter, the rear sensor barely changes; if it starts moving almost like the front one, the computer concludes the converter is no longer working properly.
With a steady light and no other symptoms you can normally drive to a garage, but don't put it off: there is often another problem behind it (misfires or a wrong mixture) and the car may fail the emissions test. If the light flashes or the car loses power, it is urgent.
Symptoms
- Engine warning light on, often as the only symptom
- Rotten-egg smell from the exhaust
- Less power or higher fuel consumption
- Failing the emissions test at the inspection
- Rattle at idle or on cold start if the inside of the converter has broken up
Possible causes
- Worn or damaged catalytic converter
- Faulty oxygen sensor (the sensor that measures oxygen in the exhaust)
- Exhaust leak before the catalytic converter or a cracked exhaust manifold
- Misfires or an over-rich mixture that have overloaded the converter
- Faulty thermostat or engine temperature sensor
- Outdated engine computer software
Checks for the garage
- Read the freeze frame data and the short- and long-term fuel trims
- Fix any misfire or lean condition first
- Test how both oxygen sensors respond to rich and lean mixtures
- Look for intake and exhaust leaks and check the mass air flow sensor
- Check whether the converter is clogged or damaged by comparing inlet and outlet temperatures
- Check for software updates and the manufacturer's technical bulletins
Next step
Ask the garage to rule out misfires, a lean mixture and exhaust leaks first, and to test the oxygen sensors before replacing the catalytic converter.
Go to a garage to confirm the cause before replacing the catalytic converter, which is usually the most expensive part. If the light flashes, the engine misfires or loses power, go as soon as possible.