Powertrain, generic (extended)

P2AC2 Intake Air O2 Sensor Reference Voltage Circuit High Bank 1

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P2AC2 means the reference voltage at the intake oxygen sensor of bank 1 reads above its permitted range. A reference lead shorted to a supply wire or battery voltage in the harness, a lost ground on the sensor side or water in the connector are the usual triggers; a sensor with an internally damaged cell can produce the same picture. The intake sensor sits in a damp, oil-misted environment near the crankcase ventilation and EGR inlet, so connector corrosion deserves a look. No manufacturer publishes P2AC2 with thresholds; CARB's rule for comprehensive input components and Ford's patents on the sensor itself are the basis here. As with the other faults in this family, the ECM loses its measurement of recirculated exhaust and falls back to model-based or reduced EGR, which can raise NOx. P2AC1 is the low counterpart, P2AC6 bank 2.

Likely causes

Reference wire shorted to a supply or battery voltage wire
Moisture or corrosion bridging pins in the sensor connector
Open ground on the sensor side

Symptoms

  • Check engine light on
  • EGR reduced, NOx emissions may rise

Repair estimate

DifficultyMediumDIY possible
Parts and labour€0–350
Time0.3–2 h

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

Parts involved

intake air o2 sensor b1wiring harnessecm

Related codes

P2ABFP2AC0P2AC1P2AC6P2B8A

References: patents.google.com, patents.google.com, law.cornell.edu.