Mitsubishi Eclipse 2000 P0141 Code: Replaced O2 Sensor Bank 1 Sensor 2 — Still Getting Error?

I believe that particular aftermarket O2 sensor brand is known for poor performance—especially with the included connector kit. Many users have reported issues after installing these kits, and once you remove the factory connector, you're often forced to re-install the original sensor or replace the plug entirely. Soldering O2 sensor wires is strongly discouraged because the signal wire operates at only 0.1–0.9 volts; any added resistance in the circuit will distort readings and cause inaccurate feedback to the engine control module (ECM). The fact that the P0141 code remains pending but doesn’t mature after clearing suggests the new sensor is operating just within acceptable limits—effectively making it appear only slightly better than the original faulty unit.

The code returned today with the check engine light on. Should I have instead spent $130 on a higher-quality O2 sensor? It’s frustrating—I bought this one for just $75, and it didn’t work. Is there any way to return it claiming it's defective? The problem is that it's already been installed, so I'm not sure what my options are. Any suggestions on how to proceed or whether a refund might be possible?

Hmm, Firechicken—sorry to deliver bad news, but you may have replaced the wrong sensor. In most vehicles, including the 1999 Mitsubishi Eclipse RS, 'Sensor 2' is located downstream of the catalytic converter. The car has a sensor before (Bank 1 Sensor 1) and one after (Bank 1 Sensor 2). If you mistakenly installed the upstream sensor instead of the downstream one, that would explain why the check engine light remains on. After clearing the code, it may take time for the system to relearn—so the intermittent return could be due to this delay. Check under the vehicle to see if there's another O2 sensor located after the catalytic converter. The good news is: you’ve now replaced both sensors with aftermarket parts at roughly the cost of one OEM unit. That’s not ideal, but it does highlight a critical error in installation.

For reliable performance, always use high-quality O2 sensors from reputable brands like Bosch or OEM. Aftermarket sensors can vary significantly in quality and compatibility.

P0141 refers to a catalyst system circuit fault involving Bank 1 Sensor 2 (downstream of the catalytic converter). You replaced Sensor 1, but you need the sensor located after the catalytic converter—Sensor 2. It could also be a wiring issue or a heater circuit failure. Check the voltage at the heater circuit to ensure it's receiving proper power. I’ve personally used a Bosch O2 sensor on my van and found it performs reliably over time. If the sensor were truly defective, you’d likely see a different code since Sensor 1 is in the fuel control loop—not directly involved in catalyst monitoring. However, both sensors are used to monitor catalytic converter efficiency. As a test, try removing the original sensor from its position and installing it into the downstream (Sensor 2) port—this may help confirm whether the issue lies with the sensor or wiring.