P2423
HC Adsorption Catalyst Efficiency Below Threshold (Bank 1)
- Severity
- Medium
- Driving
- Drivable — book it in
The hydrocarbon adsorption catalyst on bank 1 is no longer working well enough. This is a trap that holds unburnt fuel during the first minute or so after a cold start - the period when the main catalytic converter is still too cold to do anything - and releases it back into the exhaust to be burnt once everything is hot. Almost all of a modern engine's emissions come from that first minute, which is why the trap exists.
Possible causes
- CommonTrap aged out through normal service life
- CommonContamination from an engine burning oil or coolant
- CommonExhaust leak upstream, letting air in and confusing the measurement
- CommonRich running from an unrelated fault, overwhelming the trap
- PossibleOxygen sensor fault making the efficiency calculation wrong
- PossiblePhysical damage to the trap from an impact or from overheating
What you might notice
- Check engine light on
- Failed emissions test
- Sometimes a smell of fuel in the first minute after a cold start
- Usually no difference in how the car drives
What to check, in order
- Fix every other stored code before touching this component. Rich running, misfires and oxygen sensor faults all produce this code with a perfectly good trap, and the trap is expensive.
- Check for exhaust leaks upstream of the sensors. Air drawn in through a leak makes the measurement wrong and the trap innocent.
- Check the fuel trims. A engine running rich sends more hydrocarbons through than the trap was designed to hold.
- Confirm the oxygen sensors are working properly, since the efficiency figure is calculated from what they report rather than measured directly.
- Replace this last, not first. It is one of the more expensive parts in the exhaust and it is frequently condemned for someone else's fault.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx