What it means
The control module detects low 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 intake air oxygen sensor on bank 1 relies on a reference voltage circuit for dependable readings. P2AC1 sets when the control module measures that reference below its expected level, which can result from a short to ground, an internal sensor fault or a poor connector contact.
Common causes
Most likely first.
- Reference wire shorted to ground
- Internal short in sensor reference
- 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
- Capture freeze-frame data and review bank 1 sensor and fuel-trim readings alongside bank 2, if fitted, for clues about when the low-voltage condition occurs.
- Inspect the bank 1 sensor reference wire for chafing or contact with ground and check the sensor connector for corrosion or damaged pins.
- Measure reference voltage at the bank 1 sensor connector using the manufacturer's procedure to confirm it is low.
- Isolate the sensor as directed by service information and check whether the reference voltage recovers, which can help distinguish a sensor short from a wiring fault.
- If the voltage remains low, test the bank 1 reference wire for a short to ground and check for excessive resistance at terminals.
Common fixes
- Repair a bank 1 reference wire shorted to ground.
- Clean or replace corroded or loose bank 1 connector terminals.
- Repair damaged insulation or a pinched bank 1 sensor harness.
- Replace the bank 1 intake air oxygen sensor if it internally pulls the reference circuit low.
Can I keep driving?
A short, gentle trip is usually manageable if the engine runs normally, but expect possible poor fuel economy, hesitation or an emissions test failure. Reduce driving if it begins to run roughly.
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.