What Does P0422 Mean?
The main catalytic converter on bank 1 has been determined to be operating below the minimum efficiency threshold during warm-up monitoring. The PCM uses the upstream and downstream oxygen sensors to evaluate how well the converter is oxidizing HC and CO and reducing NOx. When the rear sensor activity too closely mirrors the front sensor, the catalyst is deemed ineffective. The driver will see the MIL with typically no noticeable performance change.
Common Causes
40%
Worn-out or poisoned catalytic converter substrate on bank 1
20%
Contaminated or lazy downstream O2 sensor providing inaccurate efficiency data
15%
Exhaust system leak near the catalytic converter affecting sensor readings
15%
Underlying fuel system or ignition problem causing chronic rich/lean condition
10%
Internal engine oil consumption fouling the catalyst with phosphorus/zinc
Diagnostic Steps
1
Run a catalyst efficiency monitor using Mode $06 data on the scan tool. Compare the test results to the minimum and maximum thresholds. Values near the fail threshold indicate a marginally performing converter.
2
Monitor downstream O2 sensor voltage at steady cruise (2000-2500 RPM). A healthy converter produces a steady 0.5-0.7V reading. Rapid switching similar to the upstream sensor confirms catalyst failure.
3
Check for oil consumption — blue exhaust smoke, oil on the spark plug tips, or a declining oil level between changes. Oil contaminants (ZDDP additives) poison the precious metals in the converter.
4
Inspect freeze frame data for fuel trim values. If long-term fuel trims were significantly off when the code set, address the fuel system issue before replacing the converter.
5
Perform a back-pressure test on the exhaust upstream of the converter. Excessive back pressure (above 1.5 PSI at idle) may indicate a partially melted/collapsed substrate inside the converter.
Estimated Repair Cost
$300 - $2,500
Parts + labor, varies by vehicle and location
The main catalytic converter on bank 1 has been determined to be operating below the minimum efficiency threshold during warm-up monitoring. The PCM uses the upstream and downstream oxygen sensors to evaluate how well the converter is oxidizing HC and CO and reducing NOx. When the rear sensor activi...
The most common cause of P0422 (Warm Up Catalyst Efficiency Below Threshold (Bank 1)) is: Worn-out or poisoned catalytic converter substrate on bank 1
Typical repair costs for P0422 range from $300 to $2,500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to continue driving for normal use. The vehicle will fail emissions testing. If the converter substrate has melted and is restricting flow, the driver will notice reduced power and potential overheating. A severely degraded converter near flammable materials is a rare fire risk.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0422 to identify the root cause.
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Quick Info
Category
Powertrain
System
Catalytic Converter / Exhaust System
Difficulty
Type
Generic (SAE)
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