The dreaded P0420 code indicates your car’s catalytic converter isn’t working efficiently. This article details a personal experience with this issue on a Honda Integra, focusing on the root cause, troubleshooting steps, and the ultimate solution.
Understanding the P0420 Code and its Causes
The P0420 diagnostic trouble code (DTC) specifically points to “Catalyst System Efficiency Below Threshold Bank 1.” “Bank 1” refers to the engine side containing cylinder #1. This code triggers when the oxygen sensors downstream and upstream of the catalytic converter report similar readings. This similarity suggests the converter isn’t effectively converting harmful exhaust gases. A common cause of this issue is excessive oil consumption leading to catalytic converter fouling.
Troubleshooting P0420: A Case Study
Initially, a clogged catalytic converter was suspected. Gutting the cat and installing an angled O2 sensor in the downstream location temporarily cleared the check engine light and restored fuel economy. However, this modification failed emissions testing. Installing a used, functional catalytic converter allowed the car to pass emissions, but this solution proved temporary as the replacement converter eventually clogged, leading to the return of the P0420 code and poor fuel economy.
The root cause was identified as excessive oil consumption. The engine was burning approximately 1.25 quarts of oil per 1000 miles at around 120,000 miles. The engine control unit (ECU), attempting to compensate for the extra oil burned, increased fuel delivery, negatively impacting fuel economy and further contributing to catalytic converter fouling.
Exploring Repair Options: Engine Replacement vs. Rebuild
Several repair shops quoted between $2,500 and $3,300 for a piston ring and valve seal replacement to address the oil consumption issue. Ultimately, a more cost-effective solution was chosen: replacing the engine with a used JDM B18B engine for $900. The cost of labor to swap the necessary components from the old engine to the new one, including a timing belt replacement, was $500. Additional new parts totaled $600, bringing the total cost of the engine replacement to around $2,000.
Results and Long-Term Solution
The engine replacement successfully resolved the P0420 code and related problems. The car has since been driven 25,000 miles, achieves 27 MPG, passes emissions tests, and remains reliable.
Conclusion: Addressing the Root Cause of P0420
While temporarily addressing the P0420 code might seem appealing, identifying and fixing the underlying issue—in this case, excessive oil consumption—is crucial for a long-term solution. Engine replacement provided a cost-effective and lasting fix, restoring vehicle performance and ensuring emissions compliance. If you’re facing a P0420 code, thorough diagnostics are essential to determine the root cause and choose the most appropriate repair strategy.
