- O2 sensor malfunction. Oxygen sensors monitor the amount of oxygen in the exhaust. A faulty O2 sensor can send incorrect signals to the engine control unit (ECU), which can cause it to activate the catalytic converter alarm.
- Faulty wiring. Damaged or loose wiring can also cause false catalytic converter alarms.
- Exhaust leaks. Exhaust leaks can cause the ECU to think that the catalytic converter is not working properly, triggering the alarm.
If you're experiencing a catalytic converter false alarm on your 1999 Honda Accord, it's important to have the vehicle diagnosed by a qualified mechanic to determine the cause.