Main Catalyst Efficiency Below Threshold (Bank 1)
The P0422 code means the vehicle's onboard diagnostic system has detected: Main Catalyst Efficiency Below Threshold (Bank 1). This is a moderate severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- hard
- Estimated cost
- $400 - $1500 (parts and labor)
Reads enhanced codes and shows real-time O2 sensor data. Verify the cat is actually bad before dropping $1,000+ on a replacement.
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Common Symptoms
- Check Engine Light illuminated
- Sulfur smell from exhaust
- Reduced fuel economy
- Failed emissions inspection
- Possible rattling from catalytic converter
Probable Causes (Ranked by Likelihood)
- Worn or contaminated main catalytic converter Very High
- Engine running rich due to fuel system issue High
- Exhaust leak upstream of downstream O2 sensor Moderate
- Faulty downstream oxygen sensor providing false readings Low
Step-by-Step Diagnostic Procedure
-
Monitor upstream and downstream O2 sensors on Bank 1 -- if downstream mirrors upstream switching, the catalyst is failing
-
Check for exhaust leaks with a visual inspection and by listening for hissing
-
Verify no active misfire codes that could cause catalyst damage
-
Check fuel trims for signs of rich running that could contaminate the catalyst
-
Tap the catalytic converter and listen for rattling of broken substrate
Frequently Asked Questions
Can I drive with code P0422?
Yes. The vehicle drives normally with a failing main catalyst. Emissions output increases, so you will fail an emissions test. Extended driving with a failing cat will not damage the engine.
How much does a catalytic converter replacement cost?
OEM catalytic converters range from $300-$1200 for the part alone. Aftermarket options are available for $150-$500. Labor typically adds $100-$300 depending on accessibility.
Can I use a universal catalytic converter?
In many states, a CARB-compliant aftermarket converter is acceptable. However, California and some states require specific CARB-certified converters. Check your local regulations before purchasing.
Sources
This page is built from documented references. Verify against your own service info before repair work.
P0422 on Diesel, EV & Equipment
The same code ID appears across other engines and platforms. The diagnostic flow varies by manufacturer — these are the platform-specific breakdowns:
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