P24F5 code meaning
NOx Sensor Delayed Response - High to Low (Bank 1 Sensor 2)
Powertrain system Generic code P24xx codes Check engine light
What P24F5 means
P24F5 is the same delay check for NOx sensor 2 on bank 1, which sits behind the SCR catalyst and judges its conversion. If its value lags when NOx at the outlet falls, the efficiency estimate is distorted and the SCR monitor could pass or fail wrongly, so the sensor must react in time. A late reaction means the first visible change comes too long after the expected drop. No manufacturer publishes P24F5. CARB separates delayed from slow response in its sensor definitions; GM's 2025 diesel table shows a 2-second delay limit in its front-sensor test P22F9 as a model for such timing. Hella points to ammonia slip and crystal residue as threats to the element. P22FD is the slow falling case; P24F4 sensor 1.
P24F5 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 2 hours
- Clears after repairAfter a drive cycle
Symptoms of P24F5
- Check engine light on
- Possibly an SCR efficiency code alongside
Common causes of P24F5
- Most likelyDEF crystals or ammonia slip attacking the rear sensor element
- PossibleAged measuring cells of sensor 2 reacting late
- Less likelyCondensate in the cold tailpipe area affecting the sensor
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Nox sensor b1s2
What each part of P24F5 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 4 | Area: auxiliary emission controls (catalytic converter, EGR, EVAP). |
| F5 | The exact fault in that area. |
What to do next
- Note P24F5 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P24F5
What does P24F5 mean?
P24F5 means "NOx Sensor Delayed Response - High to Low (Bank 1 Sensor 2)". P24F5 is the same delay check for NOx sensor 2 on bank 1, which sits behind the SCR catalyst and judges its conversion. It is a generic code, so it means the same on every make.
Is it safe to drive with P24F5?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P24F5 fail an emissions test?
Yes, it can. P24F5 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P24F5 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P24F5 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.