P2AC1Intake Air O2 Sensor Reference Voltage Circuit Low Bank 1
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- P2AC1 flags a reference voltage below the range the ECM accepts on the bank 1 intake oxygen sensor. This usually means the reference lead is shorted to ground or the sensing cell inside the sensor has broken down. Without a stable reference the ECM cannot operate the cell, so the oxygen reading used to work out the EGR rate becomes useless and recirculation is typically cut back or run open loop. No manufacturer publishes a threshold or bulletin for P2AC1. Ford's patents describe the intake sensor as a wide-band element operated at a fixed reference voltage whose pumping current carries the oxygen signal, and CARB requires such inputs to be monitored for out-of-range values. Unplug the sensor and measure the lead against ground before replacing parts. P2AC2 is the high counterpart, P2AC5 bank 2.
- What you may notice
- Check engine light on
- EGR reduced or uncontrolled, possibly higher NOx and a failed emissions test
- Likely causes
- LikelyReference wire chafed through to ground
- PossibleSensing cell of the intake oxygen sensor broken down internally
- RareSensor interface in the ECM faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €0 – €350
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.