What it means
Same as P23B1 with the heater control loop in plausible range yet not matching the heater model - aged heater or harness resistance.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The heater warms the Bank 1 Sensor 3 NOx sensor so it can measure exhaust nitrogen oxides under the required conditions. The control module compares the heater’s response with its expected model and sets P23B7 when the control loop remains in a plausible range but does not behave as expected.
Common causes
Most likely first.
- NOx sensor heater aging or degradation
- Excess resistance in heater wiring or connectors
- Intermittent heater circuit connection
- Fault in the heater control circuit
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 check heater command, feedback, and related faults for Bank 1 Sensor 3 before clearing anything.
- Inspect the Bank 1 Sensor 3 connector and heater wiring along the exhaust for looseness, corrosion, heat damage, chafing, or strained sections.
- With the circuit safely isolated as specified by the manufacturer, check heater wiring and connector continuity for excess resistance or an intermittent connection.
- Compare heater response to the commanded state in live data, including while gently moving the accessible harness, to see whether the mismatch follows the wiring.
- If wiring and connections check out, test the sensor heater and control circuit against the manufacturer's diagnostic procedure to distinguish a degraded heater from a control fault.
Common fixes
- Repair damaged or poorly routed Bank 1 Sensor 3 heater wiring.
- Clean or repair corroded or loose heater connector terminals.
- Restore a poor heater circuit connection or ground as indicated by testing.
- Replace the Bank 1 Sensor 3 NOx sensor if its heater response fails the manufacturer's tests.
- Repair the heater control circuit if sensor and wiring tests pass but control remains incorrect.
Can I keep driving?
The code alone does not indicate an immediate loss of drivability, but NOx emissions may rise and an aftertreatment warning or emissions test failure can result. Avoid ignoring it for long, especially if other exhaust-system warnings appear.
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.