Why does the engine malfunction light come on after replacing the catalytic converter?
3 Answers
Replacing the catalytic converter and having the engine malfunction light come on is most likely caused by the engine's mixture being either too rich or too lean. Here is more relevant information: 1. Precautions for using the automotive catalytic converter: Check the working condition of the oxygen sensor every 30,000 km. If it shows signs of aging or failure, clean or replace the oxygen sensor promptly. This is because both the catalytic converter and engine performance can be damaged due to a malfunctioning oxygen sensor—don't risk major damage for minor savings. 2. How the catalytic converter works: When high-temperature exhaust gases pass through the purification device, the catalyst in the catalytic converter enhances the activity of CO, HC, and NOx gases, promoting specific oxidation-reduction reactions.
Last time after I replaced the new catalytic converter, the check engine light also came on. After checking for a long time, I found that the mechanic didn't plug the oxygen sensor connector tightly during installation, resulting in abnormal signals triggering the alarm. After re-plugging it and driving a few kilometers, the light automatically went off. This taught me that after replacing parts, I must carefully check all connections, especially since exhaust pipe leaks can also trigger fault codes. Some aftermarket parts have even more troublesome quality issues - my friend once encountered a situation where the new catalytic converter's filtration efficiency didn't meet standards. After replacement, remember to have the repair shop use OBD equipment for re-matching. OEM parts are the most worry-free choice.
I've personally dealt with this situation before. If the check engine light comes on after replacing the catalytic converter, it's mostly due to installation issues. First, check for exhaust system leaks - if the gasket seal isn't properly installed, the oxygen sensor will report abnormal data. Secondly, consider whether the new part matches specifications; even a few millimeters' difference in size can affect exhaust backpressure parameters. I recommend listening to the exhaust sound after starting the engine - a hissing noise indicates leaks. Then inspect both front and rear oxygen sensors for oil contamination. Finally, use a diagnostic tool to check real-time data streams. If the rear oxygen sensor voltage fluctuates abnormally, there's an 80% chance the catalytic converter quality is substandard.
