What it means
The control module detects low voltage in the reference voltage circuit for the intake air oxygen sensor on bank 2. 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 2 intake air oxygen sensor depends on its reference voltage circuit for reliable readings. P2AC5 sets when the control module detects that voltage below the expected level, a condition that can result from a grounded reference wire, an internal sensor short 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
- Save freeze-frame data and compare bank 2 sensor and fuel-trim readings with bank 1, if fitted, to see when the low reading occurs.
- Inspect bank 2 reference wiring for chafing against ground and examine the connector for corrosion, loose or damaged pins.
- Measure the bank 2 reference voltage at the sensor connector using the manufacturer's procedure to confirm the low condition.
- Isolate the sensor as directed by service information and see whether the reference voltage returns, helping distinguish a sensor short from harness damage.
- If voltage remains low, test the bank 2 reference wire for a short to ground and check connector resistance.
Common fixes
- Repair a bank 2 reference wire short to ground.
- Clean or replace corroded or loose bank 2 connector terminals.
- Repair pinched or damaged insulation in the bank 2 sensor harness.
- Replace the bank 2 intake air oxygen sensor if it is internally pulling the reference voltage low.
Can I keep driving?
A short, gentle drive is usually possible if the engine runs normally, but fuel economy and emissions performance may suffer. Reduce driving if rough running or hesitation develops.
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.