P24CB code meaning
Reductant Tank Cap Switch Circuit
Powertrain system Generic code P24xx codes Check engine light
What P24CB means
Some SCR diesels have a switch at the DEF filler neck that tells the engine controller when the cap is opened, so a refill can be recognised and the tank level and fluid quality reassessed. P24CB is the general circuit code for this switch: the controller sees a signal that fits neither the open nor the closed state. Audi documents it together with P24CC for the 2013 to 2015 Q7 TDI in bulletin 2051053: the microswitch at the AdBlue filler neck of the active tank tends to stick, above all in hot and humid weather, and then sets the codes after refilling while guided fault finding shows nothing. The fix is an improved switch, for which the tank has to come out. Short to ground or supply and intermittent faults have their own codes P24CD to P24CF.
P24CB at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P24CB
- Malfunction indicator lamp on, often right after refilling DEF
- Refill not recognised, DEF warnings may persist
Common causes of P24CB
- Most likelyCap microswitch sticking, especially in hot and humid conditions
- PossibleCorroded connector or chafed wire at the filler neck
- Less likelyDried DEF crystals around the switch actuator
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Reductant tank cap switch
What each part of P24CB 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). |
| CB | The exact fault in that area. |
What to do next
- Note P24CB 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 P24CB
What does P24CB mean?
P24CB means "Reductant Tank Cap Switch Circuit". Some SCR diesels have a switch at the DEF filler neck that tells the engine controller when the cap is opened, so a refill can be recognised and the tank level and fluid quality reassessed. It is a generic code, so it means the same on every make.
Is it safe to drive with P24CB?
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 P24CB fail an emissions test?
Yes, it can. P24CB 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 P24CB to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will P24CB clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.