The error code P0420, indicating “Catalyst System Efficiency Below Threshold,” is a common issue that car owners might encounter. This code signals a problem with your vehicle’s catalytic converter, an essential component in reducing harmful emissions. While a failing catalytic converter is often the prime suspect, the root cause can sometimes be more intricate, such as underlying engine problems like excessive oil consumption.
One car owner experienced this firsthand with their Integra, facing a persistent P0420 code. Initially, attempts were made to bypass the issue by modifying the catalytic converter. This involved removing the internal components of the clogged catalytic converter and installing an angled oxygen (O2) sensor adapter at the downstream location. This temporarily extinguished the check engine light and improved fuel economy, but it led to failure during emissions testing. Reinstalling a used catalytic converter allowed the car to pass emissions, but this was a short-lived solution as it eventually clogged up again, bringing back the dreaded CEL and poor MPG.
Alt text: Used catalytic converter installed to temporarily fix P0420 code, highlighting a short-term solution.
The recurring catalytic converter issues pointed to a more fundamental problem: engine oil burning. The Integra was consuming a significant amount of oil – 1.25 quarts per 1000 miles – which was fouling the catalytic converter. The engine control unit (ECU) detected the extra oil being burned and attempted to compensate by enriching the fuel mixture, negatively impacting fuel economy, dropping it to as low as 19 MPG. A modified O2 sensor adapter, while masking the code, was not a viable long-term solution due to emissions regulations and the desire to reduce harmful pollutants.
Alt text: Illustration of engine oil burning, a common cause of catalytic converter failure and P0420 error code.
Considering the high cost of engine repairs such as a ring job and valve seal replacement, estimated between $2,500 and $3,300 by Midwest shops, the owner opted for a more economical approach. A used JDM (Japanese Domestic Market) engine, a B18B variant, was sourced for $900, including shipping. With an additional $500 for labor to transfer over the necessary USDM (United States Domestic Market) sensors, oil pump, brackets, and intake, along with installing a new timing belt, and $600 for new parts, the total cost amounted to approximately $2,000.
Alt text: JDM B18B engine as a cost-effective replacement option to resolve P0420 and oil burning issues.
This engine replacement effectively resolved the P0420 issue and the underlying oil burning problem. Since 2012, after driving 25,000 miles with the replacement engine, the car now achieves 27 MPG, passes emissions tests, and operates without the check engine light. This case illustrates that while the P0420 code directly points to the catalyst system, diagnosing and addressing the root cause, such as engine oil consumption, is crucial for a lasting solution. In situations where engine issues are contributing to catalytic converter failure, engine replacement can be a more effective and potentially cost-efficient long-term fix compared to repeated catalytic converter replacements or expensive engine repairs.
