Specifically for your 4-cylinder S10:
* Bank 1 refers to the bank of cylinders that contains cylinder #1. In a 4-cylinder engine, this is typically all the cylinders.
* Catalyst System refers to your catalytic converter.
* Efficiency Below Threshold means the catalytic converter isn't working as efficiently as it should be to sufficiently convert harmful exhaust emissions.
Possible Causes:
* Failing Catalytic Converter: This is the most common cause. The catalytic converter might be clogged, damaged internally, or simply wearing out due to age or high mileage.
* Oxygen Sensor Problems: A faulty oxygen sensor (O2 sensor), particularly the upstream sensor (before the catalytic converter), can cause inaccurate readings that lead to this code. A bad downstream sensor (after the catalytic converter) is less likely to directly cause a P0420, but could contribute to the problem.
* Exhaust Leaks: Leaks before the catalytic converter can affect the sensor readings and trigger the code.
* Ignition System Problems: Misfires can reduce the converter's efficiency.
* Air/Fuel Ratio Issues: An improperly functioning air-fuel system can also lead to inefficient catalytic converter performance.
What to do:
1. Check for any obvious exhaust leaks: Look for holes or damage in the exhaust system, especially near the catalytic converter.
2. Read other Diagnostic Trouble Codes (DTCs): Your P0420 may be accompanied by other codes that provide more specific clues. Use an OBD-II scanner to read all codes.
3. Have the O2 sensors checked: Testing O2 sensor performance is relatively straightforward with an OBD-II scanner.
4. Consider professional diagnosis: A mechanic can perform a thorough inspection of the entire exhaust system, test the O2 sensors, and check for misfires or other problems. They may also use a pressure test to check for leaks. This is often necessary for proper diagnosis and repair. Simply replacing the catalytic converter without investigating other potential causes might be expensive and ineffective.
Replacing the catalytic converter is a significant expense, so make sure to thoroughly diagnose the problem before undertaking that repair.
