P1620 – Thermostat Function (Nissan)

Description

The ECM detected abnormal thermostat operation.

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Symptoms

  • Overheating
  • Slow warm‑up

Causes

  • Stuck thermostat
  • Low coolant
  • Sensor issue

Diagnosis

  • Check coolant level
  • Inspect thermostat
  • Scan temperature data

Repair

  • Replace thermostat
  • Refill coolant