What it means
The heater sense circuit for the NOx sensor on Bank 1 Sensor 3 is reporting a high condition.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The heater sense circuit carries the reported heater condition for the Bank 1 Sensor 3 NOx sensor to the control module. P23B9 sets when that signal is higher than expected, such as when the sense wire contacts a supply source or the connector is compromised.
Common causes
Most likely first.
- Sense line shorted to supply
- Connector pins corroded - high contact resistance
- Supply wire pinched against B+ source
Symptoms
- Check engine light
- Possible NOx or aftertreatment warning
- Increased NOx emissions or failed emissions test
How to diagnose it
- Use a scan tool to record freeze-frame data and inspect the Bank 1 Sensor 3 heater sense value and related circuit codes.
- Inspect the sense wire and connector for pinched insulation, corrosion, loose terminals, or contact with a powered wire near the exhaust.
- With the circuit isolated according to the manufacturer's procedure, check the sense line for a short to supply and inspect terminal fit.
- Compare circuit readings with the manufacturer's specification and check for unintended supply voltage on the sense line.
- If the harness and connector are sound, test the sensor output and heater sense control circuit using the manufacturer's diagnostic procedure.
Common fixes
- Repair the Bank 1 Sensor 3 sense wire if it is pinched or shorted to a supply wire.
- Clean or repair corroded or loose connector terminals.
- Reroute and protect damaged harness sections from powered wires and hot exhaust parts.
- Replace the Bank 1 Sensor 3 NOx sensor if its sense output fails the manufacturer's tests.
- Repair the heater sense control circuit if sensor and wiring checks pass.
Can I keep driving?
If the vehicle behaves normally, cautious driving is generally possible, but the fault can increase NOx emissions and trigger an aftertreatment warning or emissions test failure. Have the circuit checked soon and heed any additional exhaust-system warnings.
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.