What Does P0423 Mean?
The heated catalytic converter on bank 1 is not achieving the expected efficiency level. Some vehicles use electrically heated catalytic converters that actively warm the substrate to reach light-off temperature faster. The PCM has determined that even with the heater functioning, the catalyst is not converting pollutants efficiently enough. The driver will see the check engine light and may notice a slight sulfur/rotten egg smell.
Common Causes
40%
Degraded or contaminated heated catalytic converter substrate
20%
Failed catalyst heater element preventing proper light-off temperature
15%
Downstream O2 sensor reading inaccurately due to contamination or age
15%
Chronic rich running condition accelerating catalyst deterioration
10%
Exhaust leak allowing false air into the catalyst monitoring circuit
Diagnostic Steps
1
Check for companion codes related to the catalyst heater circuit (P0429, P0030-P0038). If the heater has failed, the converter may not be reaching optimal operating temperature.
2
Monitor upstream and downstream O2 sensor waveforms at steady 2500 RPM for 60 seconds. A healthy heated cat should show a stable downstream signal. Switching downstream signal indicates catalyst failure.
3
Verify the catalyst heater is receiving power by checking for voltage at the heater connector with key on. Measure heater element resistance — typical spec is 2-10 ohms depending on the application.
4
Use an IR thermometer to measure converter surface temperature at the inlet and outlet. The outlet should be 50-100°F warmer. If the inlet and outlet are at similar temperatures, the converter is not catalyzing.
5
Check for excessive oil consumption or coolant leaks (head gasket, intake gasket) that could contaminate and poison the catalyst material.
Estimated Repair Cost
$350 - $2,800
Parts + labor, varies by vehicle and location
The heated catalytic converter on bank 1 is not achieving the expected efficiency level. Some vehicles use electrically heated catalytic converters that actively warm the substrate to reach light-off temperature faster. The PCM has determined that even with the heater functioning, the catalyst is no...
The most common cause of P0423 (Heated Catalyst Efficiency Below Threshold (Bank 1)) is: Degraded or contaminated heated catalytic converter substrate
Typical repair costs for P0423 range from $350 to $2,800, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to continue driving. Higher emissions will cause an emissions test failure. If the converter substrate has broken apart, fragments can restrict exhaust flow and cause power loss. Monitor exhaust temperatures to avoid overheating situations during extended driving.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0423 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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