P24CFReductant Tank Cap Switch Circuit Intermittent/Erratic
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- P24CF is stored when the DEF cap switch signal jumps between states or drops out briefly although nobody touches the cap, typically while driving over rough roads. The controller counts unexpected changes and flags the circuit as unstable even if every single value lies within limits. Loose terminals, a cracked solder joint in the switch or a harness rubbing on the tank are the usual reasons. No manufacturer documents P24CF publicly. On the 2013–2015 Q7 TDI, Audi bulletin 2051053 found that the cap switch at the active tank sticks and sets P24CB/P24CC; a switch that sticks only partly can also produce erratic signals. CARB requires inputs to be checked for erratic behaviour. Wiggling the harness while watching live data usually reproduces the fault.
- What you may notice
- Malfunction indicator lamp, sometimes coming and going
- Spurious refill or cap-open messages
- Likely causes
- LikelyLoose or corroded terminal in the switch connector
- PossibleSwitch that sticks only partly and chatters
- RareHarness rubbing on the tank or body
- 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: €50 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.