('07 Cobalt, Ecotec 2.2L)
I came on the text below in the AllData (paywalled) service manual. It seems like they're saying that ambient air comes into the exhaust 'oxygen' sensor (pic below) ... through the wires? Through some 'gap' between the wire and its surrounding insulation? ("Sharp bends or kinks could block the reference air path through the lead wire.")
This seems so outside of anything I've every heard of that I wonder if I'm just reading it wrong?
Heated Oxygen and Oxygen Sensor Notice
Notice: Do not remove the pigtail from either the heated oxygen sensor (HO2S) or the oxygen sensor (O2S). Removing the pigtail or the connector will affect sensor operation. ...
Do not repair the wiring, connector or terminals. Replace the oxygen sensor if the pigtail wiring, connector, or terminal is damaged.
This external clean air reference is obtained by way of the oxygen sensor signal and heater wires. Any attempt to repair the wires, connectors, or terminals could result in the obstruction of the air reference and degraded sensor performance.
The following guidelines should be used when servicing the heated oxygen sensor:
Do not apply contact cleaner or other materials to the sensor or vehicle harness connectors. These materials may get into the sensor causing poor performance.
Do not damage the sensor pigtail and harness wires in such a way that the wires inside are exposed. This could provide a path for foreign materials to enter the sensor and cause performance problems.
Ensure the sensor or vehicle lead wires are not bent sharply or kinked. Sharp bends or kinks could block the reference air path through the lead wire.
Ensure that the peripheral seal remains intact on the vehicle harness connector in order to prevent damage due to water intrusion. The engine harness may be repaired using Packard's Crimp and Splice Seals Terminal Repair Kit. Under no circumstances should repairs be soldered since this could result in the air reference being obstructed.