What it means
The control module detects a circuit fault for the NOx sensor at bank 1, sensor 3.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The NOx sensor at bank 1, sensor 3 measures nitrogen oxides in the exhaust for the emissions control system. P23AC indicates an electrical circuit fault associated with that specific sensor, which may interrupt its signal or power and can lead to NOx or DEF warnings.
Common causes
Most likely first.
- NOx sensor bank 1 sensor 3 failure
- Open, short, or damaged sensor wiring
- Loose or corroded connector
Symptoms
- Check engine light or NOx warning on
- AdBlue/DEF level or quality warning
- Possible no-start countdown after ignore period
- Failed emissions inspection (NOx)
How to diagnose it
- Record freeze-frame data and related NOx or aftertreatment codes, then check live data for bank 1 sensor 3 to see whether its signal is missing or implausible.
- Check for DEF or AdBlue warnings and any start countdown, and note the vehicle's displayed limit.
- With the exhaust cool, inspect bank 1 sensor 3's connector and harness for heat damage, chafing, corrosion, loose pins, or an open wire.
- Use the wiring diagram to check the sensor circuit for opens or shorts and verify its supply and ground against the manufacturer's specification.
- If the wiring and connections pass, test bank 1 sensor 3 and its module communication using the manufacturer's procedure.
Common fixes
- Repair an open, shorted, or heat-damaged wire in the bank 1 sensor 3 circuit.
- Clean or repair a loose or corroded sensor connector.
- Restore a faulty sensor supply or ground if diagnosis identifies it.
- Replace bank 1 sensor 3 if circuit tests show the sensor has failed.
- Repair a module or communication fault only if testing confirms it is involved.
Can I keep driving?
Have the circuit checked promptly because an active NOx sensor fault can affect emissions monitoring and may trigger a DEF warning or start countdown on some vehicles. Follow any countdown shown and avoid postponing diagnosis.
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.