Trouble CodesGM OBD Trouble CodesGM Code 15

CODE 15 - Coolant Temp Sensor Circuit

Trouble Code 15 indicates that the Coolant Temperature Sensor (CTS) is reporting abnormally low readings. CTS is used to control fuel mixture, timing, idle speed, TCC and EGR operation, among others. The thermistor used has a high resistance when cold, lowering as the coolant warms. This error then, indicates a very high resistance in the CTS circuit.

The conditions for setting this code are:

  • the coolant temperature reported is < -29 deg F (-34 deg C), and
  • the above condition is present for more than 4 seconds

NOTE: A default temperature of 111 deg F is used while the error is present.

Refer to the Code 14 description for typical sensor resistance values.

Typical causes for this code include:

1) Open circuit in CTS-ECM harness
2) Defective Coolant Temperature Sensor (resistance too high)
3) Open sensor ground circuit
4) Defective ECM

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