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P24CD

Reductant Tank Cap Switch Circuit Low

Same as P24CB with the signal shorted to ground. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.

  • Check engine light: Yes
  • Emissions related: Yes
  • Repair difficulty: easy

Symptoms

  • Check engine light or NOx warning on
  • AdBlue/DEF level or quality warning
  • Possible no-start countdown after ignore period
  • Failed emissions inspection (NOx)

Common causes

Ordered by how often each turns out to be the cause.

  • Signal shorted to groundCommon
  • Connector pins corroded - high contact resistanceLess likely
  • Harness chafing through insulationLess likely

Parts involved

  • Reductant Tank Cap Switch

P24CD is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.