OBD Reductant Tank Cap Switch Circuit Low
What it means
P24CD stands for Reductant Tank Cap Switch Circuit Low. P24CD is a P code, so the fault sits in the engine, transmission and emissions systems. For P24CD, the second digit places it in auxiliary emission controls. For P24CD, work through the cause list below, cheapest checks first.
Where it lives
For P24CD, the switch sits on the circuit this code reports. The description of P24CD reports a fault at the switch.
What to check first
For P24CD, pull the connector and inspect the terminals for spread, corrosion or backed-out pins before testing anything else.
Check these first
- P24CD: Carbon buildup or blockage in the EGR, EVAP, or air injection system
- P24CD: Failed solenoid, valve, or pump in the auxiliary emissions circuit
- P24CD: Wiring, connector, or fuse fault for the emission component
- P24CD: Small leaks in vacuum or EVAP lines
- P24CD: Failing catalytic converter or oxygen sensor reporting incorrectly
What to do next
P24CD is a fault in the auxiliary emission controls system. The steps below are general, so what actually failed on your vehicle may not be what P24CD names.
- P24CD: Read related codes and freeze frame with an OBD-II scanner
- P24CD: Inspect hoses, valves, and solenoids for leaks, cracks, or carbon buildup
- P24CD: Smoke test the EVAP or intake system if a leak is suspected
- P24CD: Command components on/off with a scan tool and watch them respond
- P24CD: Clean or replace the blocked or failed component
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Updated
Generic SAE J2012 definition. Last updated 2026-08-30.