Powertrain, generic (extended)

P2AC3 Intake Air O2 Sensor Reference Voltage Circuit/Open Bank 2

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P2AC3 is the open circuit fault in the reference voltage lead of the intake air oxygen sensor assigned to bank 2. A second intake sensor only exists where each cylinder bank has its own intake or EGR path, for example on V engines with two separate charge air routes; engines with a single sensor use the bank 1 code P2ABF. No manufacturer has published P2AC3 or a vehicle using it. Technically the check works as on bank 1: if the reference wire to the sensing cell is interrupted, the ECM can no longer operate the cell and receives no usable oxygen value, so EGR on that bank runs without feedback. Wiring routed close to the hot turbo or exhaust of the second bank is the first place to look. P2AC4 is the plausibility fault, P2AC5/P2AC6 low/high.

Likely causes

Broken reference wire or loose terminal at the bank 2 sensor
Harness damaged by heat near the bank 2 turbocharger or exhaust
Sensing cell of the bank 2 intake oxygen sensor internally open

Symptoms

  • Check engine light on
  • EGR on bank 2 reduced or uncontrolled

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 b2wiring harnessecm

Related codes

P2AC4P2AC5P2AC6P2ABFP2AEC

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