P0431 code meaning
Catalyst 1 Efficiency Below Threshold Bank 2
Powertrain system Generic code P04xx codes Check engine light
What P0431 means
Catalyst 1 is the first catalyst in the flow direction of bank 2 (the side without cylinder 1) – the close-coupled or warm-up catalyst that lights off first after a cold start; the older wording was Warm Up Catalyst. P0431 means it no longer converts enough. Mitsubishi V6 engines with manifold catalysts and GM's 3.0/3.2-litre V6 of 2004/05 with Bosch control report it: the rear sensor amplitude is compared with a model, and a quality factor above 0.625 (2004) or 0.375 (2005) sets the code after two trips. A Mitsubishi bulletin names coating coming off the manifold catalysts.
P0431 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor1 to 3.5 hours
- Clears after repairAfter a drive cycle
Symptoms of P0431
- Check engine light on, otherwise often no change in driving
- Emissions test failed (higher HC, CO, NOx)
- Rattling or loss of power if the catalyst has broken up
Common causes of P0431
- Most likelyClose-coupled catalyst aged, overheated or coating detached
- PossibleMisfire or rich running as prior damage
- PossibleSensor after the close-coupled catalyst sluggish or faulty
- Less likelyEngine module software (Mitsubishi: update for 2006 Eclipse V6)
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Close coupled catalystDownstream oxygen sensorEngine control module
What each part of P0431 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 4 | Area: auxiliary emission controls (catalytic converter, EGR, EVAP). |
| 31 | The exact fault in that area. |
What to do next
- Note P0431 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0431
What does P0431 mean?
P0431 means "Catalyst 1 Efficiency Below Threshold Bank 2". Catalyst 1 is the first catalyst in the flow direction of bank 2 (the side without cylinder 1) – the close-coupled or warm-up catalyst that lights off first after a cold start; the older wording was Warm Up Catalyst. It is a generic code, so it means the same on every make.
Is it safe to drive with P0431?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P0431 fail an emissions test?
Yes, it can. P0431 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0431 to fix?
Difficulty: medium. A typical repair takes 1 to 3.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0431 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.