GM OBD Trouble Code 15

Auto Systems and Repair

Engine Coolant Temperature Sensor Error (Low Temp Indicated)

The Coolant Temperature sensor sends a signal to the Engine Control Computer based on the temperature of the engine. The ECM uses the information from this sensor to help calculate fuel delivery and spark timing. If it's necessary, it will also activate the cooling fans.

Fault Code Description

Symptoms

  • Engine running too rich (hard starting or black smoke from exhaust)
  • The engine cooling fan may run constantly

Common Problems

  • A failed coolant temperature sensor is the most common cause of a Code 15
  • A quick test for the coolant temperature sensor circuit from the ECM would be to unplug the temp sensor and watch the coolant sensor reading on the scan tool while jumping the harness side of the sensor connector. The scan readings should switch from full cold to full hot when inserting and removing the jumper from the connector.
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