P24CB Reductant Tank Cap Switch Circuit
What does P24CB mean?
P24CB — Reductant Tank Cap Switch Circuit. This is an OBD-II diagnostic trouble code a scanner retrieves when your vehicle's computer detects reductant tank cap switch circuit. The level of risk depends on how the vehicle is currently running and how long you've been driving with the light on.
Common causes of P24CB
- Carbon buildup or blockage in the EGR, EVAP, or air injection system
- Failed solenoid, valve, or pump in the auxiliary emissions circuit
- Wiring, connector, or fuse fault for the emission component
- Small leaks in vacuum or EVAP lines
- Failing catalytic converter or oxygen sensor reporting incorrectly
How to fix P24CB
These are general steps for this system. The exact cause depends on your vehicle — confirm with live scan data before replacing parts.
- Read related codes and freeze frame with an OBD-II scanner
- Inspect hoses, valves, and solenoids for leaks, cracks, or carbon buildup
- Smoke test the EVAP or intake system if a leak is suspected
- Command components on/off with a scan tool and watch them respond
- Clean or replace the blocked or failed component