Updated at: 29-03-2022 - By: micdot

This article contains affiliate links. A modest compensation may be earned by me if you decide to make a purchase after clicking on one of my links. So, what are the signs of a failed downstream O2 sensor? The dashboard’s check engine light will typically come on if an O2 sensor (upstream or downstream) fails. Other signs, such as a decrease in engine performance, show that your car’s downstream O2 sensor is failing or has already been damaged. The downstream sensor measures the degree of pollution in the emissions released from the CAT to the muffler, which would subsequently go via the tailpipe and into the atmosphere. –> Because of this, it is imperative that downstream O2 sensors be replaced as they begin to fail.

Bad Downstream O2 Sensor Symptoms

The following are common signs of a failed downstream oxygen sensor in a vehicle. Before concluding that the anomaly is caused by a defective downstream O2 sensor, you should perform a check – troubleshoot your car – when you encounter these indicators.

1. Your Vehicle Won’t Pass Emissions Tests

If your car fails an emissions test, one of the possible causes is a malfunctioning or defective oxygen sensor. Modern cars have O2 sensors built into the emissions system, so if one fails, you can bet your car won’t pass the test. To be on the safe side, your car may fail an emissions test due to problems with the catalytic converter or muffler or exhaust manifold; therefore, you should investigate your emissions system to see which part is to blame for the failure.

3 Common Bad Downstream O2 Sensor Symptoms

2. Check Engine Light (CEL) Is On

The check engine light might come on for a variety of reasons, one of which is a defective or failed downstream sensor. What causes the check engine light to come on when an O2 sensor is faulty?

Simply put, the ECU receives information from the O2 sensors, and when the sensors send incorrect signals, the ECU interprets this as an error message, resulting in the CEL illumination on your dashboard.

3. Drop In Engine Performance

Every part of a car is interrelated, so when one fails, it can influence other parts, and as a result, your engine’s performance can be affected as a result. That being said, an ill-functioning O2 sensor will likely have an impact on the ECU, which in turn will have an impact on the engine.

How To Tell If An Oxygen Sensor Is Bad | The Motor Guy

What More?

For the most part, the downstream and upstream oxygen sensors operate in different ways. ECUs aren’t affected if downstream sensors fail, but the ECUs are affected if downstream sensors fail, and the ECUs are affected if downstream sensors fail. The first thing you should do if you see any of these downstream O2 sensor warning signs is to do a thorough check of your car to be sure that the symptoms were caused by a defective downstream sensor. Afterwards, you should try to replace the defective sensor(s). O2 sensors can be replaced for a relatively low price. As a result, some motorists are willing to replace all of the sensors at once.