You can’t see reference air on a scan tool, but problems with it can certainly affect what you see.
Oxygen sensors and air-fuel ratio sensors operate by evaluating differences in oxygen concentration. One side of that comparison involves the exhaust stream. The other involves reference air — essentially atmospheric air that provides the sensor with a known oxygen concentration for comparison.
Maintaining that reference is critical to producing an accurate sensor signal.
That’s why physical damage to an oxygen sensor shouldn’t be dismissed as merely cosmetic. Damaged wiring, a compromised connector, a bent sensor housing or cracked ceramic components can allow exhaust gases or underhood contaminants to interfere with the sensor’s reference air.
The result could be inaccurate readings, sluggish sensor response, a sensor that stops producing a useful signal or oxygen sensor and air-fuel ratio diagnostic trouble codes.
There’s another important diagnostic takeaway: damaged oxygen sensor wiring shouldn’t automatically be treated like ordinary wiring that can simply be spliced back together. The wiring and connector can be part of the pathway that allows reference air to reach the sensor.
That means a repair that restores electrical continuity may not necessarily restore proper sensor operation.
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This video is presented by Auto Value and Bumper To Bumper.
