P0431: Catalyst 1 Efficiency Below Threshold Bank 2
What Does P0431 Mean?
P0431 is a diagnostic trouble code indicating: Catalyst 1 Efficiency Below Threshold Bank 2. This code relates to the emission controls system. It has been reported in NHTSA complaints across 2 different vehicle models.
The emission control system reduces harmful exhaust pollutants through several subsystems: EGR (Exhaust Gas Recirculation) recirculates a portion of exhaust back into the intake to lower combustion temperatures and reduce NOx. The secondary air injection system pumps fresh air into the exhaust during cold starts to help the catalytic converter light off faster. The catalytic converter converts CO, HC, and NOx into CO2, H2O, and N2. The EVAP system captures fuel vapors from the tank and purges them into the engine for combustion. When any of these systems malfunction, the vehicle will fail emissions testing and the ECM will set a DTC.
Symptoms of P0431
- ⚠️ Check engine light on
- ⚠️ Failed emissions/smog test
- ⚠️ Possible rough idle or stalling (EGR stuck open)
- ⚠️ Fuel smell (EVAP leak)
- ⚠️ Reduced performance in some cases
- ⚠️ Increased tailpipe emissions
Common Causes
- 🔍 Carbon buildup causing EGR valve to stick
- 🔍 EVAP system leak (gas cap, hose, canister, purge valve)
- 🔍 Catalytic converter below efficiency threshold (aging)
- 🔍 Secondary air pump failure or check valve stuck
- 🔍 Wiring or vacuum line issue in emission control circuit
P0431 Reports by Year
Real Owner Reports
From NHTSA complaint database — actual owner descriptions.
"VW Tiguan lost significant acceleration while driving on the highway. Vehicle check engine light came on. Felt like vehicle was going to stall and decelerated to a below highway required speed. Vehicle was inspected by a VW authorized service center and . Verified GFF found DTC's P0431, P04F0, P2"
— Volkswagen Tiguan owner, 04/18/2025
"2006 JEEP WRANGLER SPORT LESS THEN 60,000 MILES ON IT AND KEEPS GETTING SERVICE CODE P0431 P0431-CATALYST WARM UP EFFICIENCY BELOW THRESHOLD ALL 4 OXYGEN SENSORS REPLACED AND STILL GETTING CODE. *TR"
— Jeep Wrangler owner, 09/11/2010
Source: NHTSA Complaints Database
Most Reported Vehicles for P0431
Based on NHTSA owner complaint data.
| # | Vehicle | Reports |
|---|---|---|
| 1 | JEEP WRANGLER | |
| 2 | VOLKSWAGEN TIGUAN |
Diagnostic Tips
- For EVAP codes: start with the gas cap — tighten it and clear the code. If it returns, use a smoke machine to find the leak
- For EGR codes: remove and inspect the EGR valve — carbon buildup causing sticking is extremely common and cleanable
- For catalyst codes: check upstream O2 sensor first — a bad sensor can falsely report low catalyst efficiency
- For secondary air codes: listen for the air pump running during cold start — it should run for 30-90 seconds
Common Mistakes to Avoid
- ❌ Replacing the catalytic converter based on a P0420/P0430 code alone — diagnose the root cause first (O2 sensor, exhaust leak, engine running rich)
- ❌ Ignoring a loose gas cap as the cause of EVAP codes — this is literally the #1 cause and the cheapest fix
- ❌ Using aftermarket catalytic converters in states with strict emissions laws (California) — CARB-compliant converters are required
Frequently Asked Questions
Will I pass emissions with a check engine light on?
Can I just clear the code before emissions testing?
How much does a catalytic converter cost?
What To Do Next
Possible Fixes
- 🔧 Clean or replace EGR valve
- 🔧 Replace gas cap (EVAP codes)
- 🔧 Replace EVAP purge or vent solenoid
- 🔧 Replace catalytic converter
- 🔧 Replace secondary air pump or check valve
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1
Find your vehicle above
Click your make and model for real owner reports and common causes specific to your vehicle.
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2
Check for recalls
Go to nhtsa.gov/recalls and enter your VIN. Free repairs if covered.
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Get a professional diagnosis
A code alone doesn't identify the exact failed part. A diagnostic ($50–$150) pinpoints the root cause.