What it means
The Bank 1 Sensor 2 NOx sensor responds too slowly to a high-to-low change. The code does not identify why the response is delayed or its effect on a particular monitor.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Bank 1 Sensor 2 is the NOx sensor identified by the control system as Sensor 2 on Bank 1, typically downstream of the relevant aftertreatment component. The module monitors how quickly this sensor's NOx reading falls during a high-to-low change. P24F5 sets when Bank 1 Sensor 2 responds too slowly, potentially because its element has aged or its protective tube is soot-restricted.
Common causes
Most likely first.
- Aged sensor element with reduced response speed
- Soot clogging the protective tube
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
- Read freeze-frame data and related NOx or reductant codes, confirming the fault names Bank 1 Sensor 2 and records a high-to-low response delay.
- Inspect the Bank 1 Sensor 2 connector and harness for heat damage, corrosion, loose pins, or chafing near the exhaust.
- Check Bank 1 Sensor 2 live NOx data during the manufacturer's prescribed operating conditions and observe whether its reading falls too slowly.
- Inspect the sensor's protective tube for soot restriction or damage if the manufacturer's procedure permits inspection.
- Check for exhaust leaks or aftertreatment faults that could affect the downstream NOx conditions being measured.
- If wiring and exhaust conditions are sound, test or replace Bank 1 Sensor 2 according to the manufacturer's diagnostic procedure.
Common fixes
- Repair a damaged or loose Bank 1 Sensor 2 connector or harness.
- Repair an exhaust leak or aftertreatment fault affecting the downstream NOx reading.
- Clean or service a soot-restricted protective tube only if permitted by the manufacturer.
- Replace the Bank 1 Sensor 2 NOx sensor if its response remains slow and circuit checks pass.
Can I keep driving?
You may be able to drive if the vehicle runs normally, but arrange prompt repair because emissions warnings, reduced power, or a no-start countdown may follow. Do not ignore a displayed reductant countdown.
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.