P24CBReductant Tank Cap Switch Circuit
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- 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.
- What you may notice
- Malfunction indicator lamp on, often right after refilling DEF
- Refill not recognised, DEF warnings may persist
- Likely causes
- LikelyCap microswitch sticking, especially in hot and humid conditions
- PossibleCorroded connector or chafed wire at the filler neck
- RareDried DEF crystals around the switch actuator
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €100 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.