Powertrain, generic (extended)

P2A01 O2 Sensor Circuit Range/Performance Bank 1 Sensor 2

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modeNo

Sensor 2 on bank 1 sits behind the catalytic converter and mainly serves to judge how well the converter stores oxygen. Ford uses P2A01 for a signal that is out of range on the low side: on petrol engines with certain Continental control modules from 2011, and still in its 2020–2023 summary, a reading under −0.2 V lasting 10 s sets the code, usually because signal and return wires are swapped or the sensor is worn. On diesels this position is often taken by a NOx sensor with an oxygen output: Ford checks it against a calculated oxygen level, and GM's 2025 diesel tables let it differ from sensor 1 by at most 6 % at full load (120 of 240 samples, Type B). Mazda's CX-9 bulletin SA-004/19 links it to engine oil inside connector C-34 from a leaking oil pressure switch.

Likely causes

Downstream sensor worn or contaminated

Engine oil or moisture in the sensor connector (Mazda CX-9 connector C-34)

Signal and return wires swapped, e.g. after a sensor replacement

On diesels, oxygen output of the second NOx sensor drifting

Symptoms

Check engine light on
Catalyst or aftertreatment monitor stays incomplete
Usually no noticeable change in driving behaviour

Repair estimate

DifficultyEasyDIY possible

Parts and labour€60–450

Time0.3–1.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

oxygen sensorcatalytic converter

References: law.cornell.edu, newtonnet.co.uk, fordservicecontent.com, fordservicecontent.com.