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P278D

Kick Down Switch Circuit High

Voltage on the kick-down switch line is above the expected window. 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: No
  • Repair difficulty: easy

Common causes

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

  • Open switch contactsCommon
  • Switch wire shorted to B+Possible
  • Connector pins corroded - high contact resistanceLess likely

Parts involved

  • Kickdown Switch
  • Wiring Harness

P278D 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.