Talking To Customers About Oxygen Sensors

May 06, 2023

Here are some examples of how you can filter through the technical mumbo-jumbo regarding how sensors work to arrive at an explanation that your customers can better understand.

Technician: The OBD II system monitors converter efficiency by comparing the upstream and downstream oxygen sensor signals. If the converter is doing its job and is reducing the pollutants in the exhaust, the downstream oxygen sensor should show little activity (few lean-to-rich transitions, which are also called "crosscounts"). The sensor's voltage reading should also be fairly steady (not changing up or down), and average 0.45 volts or higher.

Customer Translation: O2 sensors are placed before and after the converter to measure how the converter is changing exhaust gases, as well as how the engine is performing. One sensor measures what goes in and the other measures what comes out of the converter.

Technician: If the signal from the downstream O2 sensor starts to mirror that from the upstream oxygen sensor(s), it means converter efficiency has dropped off and the converter isn't cleaning up the pollutants in the exhaust. The threshold for setting a diagnostic trouble code (DTC) and turning on the Malfunction Indicator Lamp (MIL) is when emissions are estimated to exceed federal limits by 1.5 times.

Customer Translation: If the O2 sensor at the rear of the converter sees an increase in emissions that exceeds a preset limit, it will turn on your Check Engine light.

Technician: Additional diagnostics may be needed to confirm if the oxygen sensor or converter is failing, if the upstream and downstream O2 sensors are functioning properly and show a dropoff in converter efficiency.

Customer Translation: Both oxygen sensors and catalytic converters are very expensive to replace. The code is not the "be-all-end-all" in determining what needs to be replaced. A code points at the symptoms and not at the diagnosis. The technician also needs to confirm if something upstream in the engine is harming the oxygen sensors and converters. If we do not do this, you will be back.