What it means
The heater sense circuit for the NOx sensor on Bank 1 Sensor 3 is reporting a low 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 reports the heater condition for the NOx sensor at Bank 1 Sensor 3 to the control module. P23B8 sets when that sense signal is lower than the module's expected range, which can happen if the line is grounded or its connection is compromised.
Common causes
Most likely first.
- Sense line shorted to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
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 save freeze-frame data and check the Bank 1 Sensor 3 heater sense reading and any related voltage or aftertreatment codes.
- Inspect the sensor connector and sense wire for corrosion, damaged insulation, chafing, or contact with the exhaust or chassis.
- Check the sense-line terminal fit and continuity with the circuit isolated, following the manufacturer's procedure, since a damaged or resistive connection can distort the reading.
- Test whether the sense line is shorted to ground and compare circuit readings with the manufacturer's specification.
- If the harness and connector test correctly, test the NOx sensor heater sense output and its control circuit using the vehicle's diagnostic procedure.
Common fixes
- Repair a chafed or grounded Bank 1 Sensor 3 heater sense wire.
- Clean or repair corroded or loose connector terminals.
- Restore damaged harness routing or insulation to prevent renewed contact with ground.
- Replace the Bank 1 Sensor 3 NOx sensor if its heater sense output fails the manufacturer's tests.
- Repair the heater sense control circuit if wiring and sensor tests pass.
Can I keep driving?
You can generally drive cautiously if the vehicle otherwise runs normally, but the fault may increase NOx emissions and cause an aftertreatment warning or emissions test failure. Arrange diagnosis soon, and stop if a separate warning indicates a more serious exhaust or engine problem.
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.