Knowing when your car’s oxygen sensor has failed can save hundreds of dollars in diagnostic fees and wasted parts. The oxygen sensors are a vital part of the engine management system and are used to perform two very important functions.
The bank 1 O2 sensor is typically mounted in your vehicle’s exhaust manifold and monitors the air/fuel mixture (ratio of parts air and parts fuel being consumed), while the downstream or bank 2 O2 sensors are used to monitor the performance of your vehicle’s catalyst.
Most O2 sensors generate a rich or lean voltage signal depending in on how much unburned oxygen is metered to be flowing through the vehicle’s exhaust, usually mounted near the collector on the manifold where exhaust from each combustion chamber meets. A few, like the heated ceramic O2 sensors in some Nissans, older Jeeps, and Eagle, vary in resistance to indicate a rich or lean condition in the exhaust, instead of the traditional voltage signal, but these are far less common.
The most common of symptoms related to a faulty oxygen sensor is a sudden (significant and almost immediately noticeable) drop in your vehicles fuel economy. Another immediate effect of a defective sensor is a drastic change engine performance, overall power and response. But there are other tells that could point to a faulty sensor, for example your car could idle significantly harsher then normal, or sporadically fluctuate idle. Also an odor from your exhaust from of the extra fuel being consumed is possible as well.
Generally, for fuel management purposes, your engine’s ECU would use the input from the bank 1 O2 sensor to readjust the fuel mixture as needed for optimum emissions, fuel economy and performance. This is why a common complaint for below average fuel economy, weaker than normal engine responsiveness, and performance is routed to a faulty front O2. Signal for the second bank of oxygen sensors is used primarily to detect any problems with the vehicles catalyst, and to tune in fuel trim. Many late model vehicle are replacing the traditional bank 1 sensor for an air/fuel sensor (which is just another name for a wide-band oxygen sensor) to monitor the fuel mixture.
The wide operating range of wide-band O2 sensors allows for faster reaction to correcting fuel trim and keeps the engine’s operating range as close to stoichiometry (14.7:1 air fuel ratio), as possible. In doing so this keeps newer engines capable of reducing emissions by a great deal, keeping engines more compliant to the stricter emissions laws of today. But these systems also make these sensors far more expensive than the average automotive oxygen sensor.
Now the OBD 2 system should detect if any faults with your vehicle’s oxygen sensors are present, whether there are related to the internal heater or the circuit leading to your sensor and set one or more fault codes turning on the check engine light. If diagnosis confirms a faulty sensor (and not a wiring issue or alternate engine fault that could cause a similar situation), the sensor should be replaced.
It has been my experience that vehicles with multiple bank sensors, where a bank 1 sensor failed, the other bank 1 sensor on the opposite bank will likely need replacing as well (I feel as if I have yet to own a car that did not almost immediately need a matching bank sensor when replacing the originating fault sensor). Though some front sensors can be costly, replacing both at the same time ensures you get the best possible performance and fuel economy, given the importance to fuel mixture.
The bank 2 oxygen sensors tend to outlast front O2’s as they are behind the catalyst and are exposed for far less heat than normal. However they are also exposed to more road debris given their positioning and open space. Though most people rather not, I usually recommend replacing any bank 2 oxygen sensors when a catalyst is replaced as to better ensure the life of a new catalyst, but also to adhere to the policies of some catalytic converter manufacturer warranties.
Now you can get oxygen sensors in two variants; exact fit units and universal sensors. Exact fit O2 sensors come with the complete connection harness and are “plug and play” made per application. Universal units are simply pig tail sensors that would require you to cut and splice them into your vehicles original sensor using that connector to meet to your existing harness, but allow suppliers to offer fewer part numbers that cover larger ranges of applications.
Some people are hesitant to using the universal type sensor given the work entailed to install them, but for vehicles with the harder to source sensors or stranger engine combinations they are better for those with non US applications. A universal sensor was the only option I had for a Nissan I had previously where the engine was from a vehicle not offered here in the states. Splicing was easy and operation was just as good as the original when it was in working order. Also offer a more economical alternative to direct fit units.
About The Author: Mike Rivera