Powertrain, generic (extended)

P24CF Reductant Tank Cap Switch Circuit Intermittent/Erratic

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

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.

Likely causes

Loose or corroded terminal in the switch connector
Switch that sticks only partly and chatters
Harness rubbing on the tank or body

Symptoms

  • Malfunction indicator lamp, sometimes coming and going
  • Spurious refill or cap-open messages

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–600
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

reductant tank cap switch

Related codes

P24CBP24CCP24CDP24CE

References: law.cornell.edu, static.nhtsa.gov.