Powertrain, generic (extended)

P2A02 O2 Sensor Circuit Range/Performance Bank 1 Sensor 3

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

Sensor 3 on bank 1 follows a second converter or, on diesels, a further aftertreatment stage. GM is the only maker found that documents P2A02: in its 2025 diesel tables the oxygen value of the third NOx sensor is held against that of sensor 2 while the engine runs at full load, and a gap of more than 6 % in either direction in 120 of 240 samples sets a two-trip Type B fault. The test only starts once both sensors report themselves fully operational and the sensor-2 check has run, so a fault further upstream shows up as P2A01 first. For petrol engines with a third sensor no public description of this code exists; there CARB's rule applies that downstream sensors must stay good enough for converter monitoring. A drifting sensor 3 hardly changes how the car drives but stops the aftertreatment checks.

Likely causes

Oxygen output of the third NOx or oxygen sensor drifting with age
Exhaust leak between sensor 2 and sensor 3 lets outside air in
Sensor coated with soot, ash or urea deposits

Symptoms

  • Check engine light on
  • Aftertreatment monitor does not complete
  • No noticeable effect on driving in most cases

Repair estimate

DifficultyMediumDIY possible
Parts and labour€100–600
Time0.5–2 h

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

Parts involved

oxygen sensorcatalytic converter

Related codes

P0142P0145P2274P2A01P2A05P2A08

References: law.cornell.edu, gsi.ext.gm.com.