P24CDReductant Tank Cap Switch Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- P24CD means the signal line of the DEF cap switch sits below its valid voltage band. With the usual pull-up input that points to the line being pulled to ground: a short in the harness near the filler neck, a switch with an internal short, or moisture bridging the contacts. Whether the controller then reads the cap as permanently open or closed depends on how the switch is wired. No manufacturer documents P24CD publicly. The same switch appears in Audi's bulletin 2051053 for the Q7 TDI with the general and range codes P24CB and P24CC, which shows where it sits and that it can only be replaced with the tank out. CARB requires input circuits of emission-related components to be monitored for readings outside their valid band. The opposite case is P24CE; sporadic drops are P24CF.
- What you may notice
- Malfunction indicator lamp on
- Cap state shown permanently wrong, refills not detected
- Likely causes
- LikelySignal wire chafed through to ground near the filler neck
- PossibleMoisture or DEF in the switch or connector bridging to ground
- PossibleSwitch with internal short
- 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: €80 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.