What it means
The control module detects high voltage in the reference voltage circuit for the intake air oxygen sensor on bank 1. The sensor reading may be unreliable.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The bank 1 intake air oxygen sensor uses a reference voltage circuit to produce readings the control module can interpret. P2AC2 sets when the voltage on that circuit is higher than expected, which points toward a short to battery voltage, an overvoltage source or a poor connection affecting the reading.
Common causes
Most likely first.
- Reference wire shorted to B+
- Sensor reference regulator overvoltage
- Connector pins corroded - high contact resistance
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
How to diagnose it
- Save freeze-frame data and compare bank 1 sensor and fuel-trim live data with bank 2, if fitted, to establish when the high-voltage condition occurs.
- Inspect bank 1 reference wiring for damage or contact with a power feed, and check the connector for corrosion or loose pins.
- Measure the reference voltage at the bank 1 sensor connector using the manufacturer's procedure to verify it is above the expected range.
- With the circuit isolated as specified, check the reference wire for a short to battery voltage and inspect adjacent harnesses for cross-contact.
- If wiring checks pass, test the sensor and its reference supply circuit for an internal fault or regulator overvoltage.
Common fixes
- Repair a bank 1 reference wire shorted to battery voltage.
- Clean or repair corroded or loose terminals at the bank 1 sensor connector.
- Separate and secure harness sections that are contacting a power feed.
- Replace the bank 1 sensor or repair its reference supply only if testing identifies it as the source of overvoltage.
Can I keep driving?
You can generally drive gently if the engine runs normally, but fuel economy may worsen and the vehicle may fail emissions testing. Stop or limit driving if the high reading is accompanied by rough running or hesitation.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.