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P2556

Engine Coolant Level Sensor/Switch Circuit

General electrical fault on the engine coolant level sensor/switch circuit. Many vehicles use a simple float-switch in the expansion tank, others use a continuous-level analog sensor. With the input invalid the ECM cannot warn for low coolant before overheating starts.

  • Check engine light: Yes
  • Emissions related: No
  • Repair difficulty: easy

Common causes

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

  • Open or shorted wiring to the sensorCommon
  • Corroded connector at the expansion tankPossible

Parts involved

  • Coolant Level Sensor
  • Sensor Wiring

P2556 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.