HC Adsorption Catalyst Efficiency Below Threshold - Bank 1
The P2423 code means the vehicle's onboard diagnostic system has detected: HC Adsorption Catalyst Efficiency Below Threshold - Bank 1. This is a moderate severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- hard
- Estimated cost
- $200 - $1500 (parts and labor)
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What Are the Symptoms of P2423?
- Check Engine Light illuminated
- Failed emissions test for hydrocarbons
- Slight fuel odor from exhaust
- No major drivability symptoms
- Reduced catalytic converter efficiency readings
What Causes P2423? (Most Likely First)
- Degraded or contaminated HC adsorption catalyst Very High
- Engine running too rich contaminating the catalyst High
- Exhaust leak before the catalyst Moderate
- Incorrect fuel type or contaminated fuel Low
Can I Still Drive with P2423?
Short distances only. P2423 is rated moderate severity. Keep trips short and get it diagnosed soon rather than waiting for symptoms to worsen.
Frequently Asked Questions
Can I drive with code P2423?
Short distances are acceptable. The vehicle will have higher hydrocarbon emissions and will fail emissions testing until repaired.
What causes P2423?
Usually a degraded HC adsorption catalyst, commonly seen on European vehicles with close-coupled catalysts. Rich running conditions accelerate catalyst degradation.
Is P2423 expensive to fix?
Costs range from $200 to $1500. Catalyst replacement on European vehicles is the most expensive repair. Address any rich-running condition first to prevent recurrence.
Mechanics Guide Step-by-step diagnosis
How Do You Diagnose P2423?
-
Check for additional fuel trim or O2 sensor codes indicating rich running
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Inspect the exhaust system for leaks before the catalyst
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Evaluate catalyst efficiency using upstream and downstream O2 sensor data
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Check fuel trims to ensure the engine is not running excessively rich
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Inspect for oil burning that could contaminate the catalyst
Sources 1
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
Which Vehicles Commonly Get P2423?
- 2012-2020 BMW 3 Series
- 2013-2021 Mercedes-Benz C-Class
- 2014-2022 Audi A4
- 2011-2019 Volkswagen Jetta
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