What it means
The control module detects a performance fault in the NOx sensor processor for bank 1, sensor 3. The code does not by itself establish that the processor is inside the control module or identify a failed part.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The NOx sensor processor handles signals for bank 1, sensor 3, the third NOx sensor identified on bank 1 by the vehicle's system. P23AB means the module has detected a processor performance problem for that sensor circuit; the code alone does not prove that the processor or the sensor itself has failed.
Common causes
Most likely first.
- Internal software anomaly
- Module software outdated, reflash may resolve
- Supply voltage outside specification
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 all related NOx and aftertreatment codes, then review live data for bank 1 sensor 3 and any available processor status.
- Check whether DEF or AdBlue warnings or a start countdown are active, and note the remaining distance or time shown by the vehicle.
- Inspect bank 1 sensor 3's connector and harness near the exhaust for heat damage, corrosion, loose pins, or chafing.
- Check the sensor system's supply and ground against the manufacturer's specification and look for related module voltage or communication faults.
- Check for applicable software updates or processor diagnostics using the manufacturer's service information before replacing the sensor or module.
Common fixes
- Repair damaged or heat-affected wiring at bank 1 sensor 3.
- Clean or repair loose or corroded connector terminals.
- Correct a supply or ground fault if testing identifies one.
- Apply a manufacturer-approved software update if it addresses the processor fault.
- Replace bank 1 sensor 3 or a related module only if testing confirms the failed component.
Can I keep driving?
Arrange diagnosis promptly because a NOx fault can trigger emissions warnings and, on some vehicles, a start countdown or no-start restriction. Follow any countdown displayed by the vehicle and avoid delaying repairs until it reaches its limit.
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.