What it means
The positive current control circuit for the Bank 1 Sensor 3 oxygen sensor is below its expected electrical range.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Bank 1 Sensor 3 is the third oxygen sensor position on the engine's Bank 1 exhaust side, and its positive-current control circuit supports the sensor's measurement function. P2A39 sets when that circuit's voltage falls below the expected range, commonly from a short to ground or a sensor or connector fault.
Common causes
Most likely first.
- Wiring short to ground
- Faulty oxygen sensor
- Poor connector contact
Symptoms
- Check-engine light
How to diagnose it
- Save freeze-frame data and review Bank 1 Sensor 3 live data to see whether its readings changed when the positive-current circuit went low.
- Inspect the Bank 1 Sensor 3 connector and exhaust-area harness for chafing to ground, heat damage, corrosion, or loose pins.
- Check the positive-current control wire for a short to ground using the manufacturer's wiring diagram and procedure.
- Inspect connector contact and test the sensor circuit for the specified electrical response against the manufacturer's specification.
- If wiring and connections pass, test Bank 1 Sensor 3 and the module circuit before replacing the sensor.
Common fixes
- Repair insulation rubbed through and grounding the positive-current control wire.
- Clean or repair poor contact at the Bank 1 Sensor 3 connector.
- Replace Bank 1 Sensor 3 if its circuit fails the specified test.
- Repair a confirmed control-module circuit fault.
Can I keep driving?
The low positive-current circuit fault can impair emissions control, even without obvious drivability symptoms. Avoid extended unnecessary driving and address it soon; stop if the engine runs poorly or the warning light flashes.
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.