Code 15, Coolant Temp Sensor (Cts) CKT, High Temp Indicated: Notes

The Coolant Temperature Sensor (CTS) uses a thermistor to control signal voltage to ECM. ECM applies voltage on Red/Yellow wire to coolant sensor. ECM monitors the voltage across the CTS and converts it into a temperature reading. When engine is cold, sensor resistance is high. ECM will sense high signal voltage. As engine warms, sensor resistance lowers and voltage drops.

Code 15 will set if voltage input at ECM indicates a coolant temperature greater than 284°F (140°C) for at least 5 seconds.

1. This test simulates Code 14. If ECM stores Code 14, ECM and wirings are okay, and CTS is faulty. If Code 15 resets, CTS is okay and wiring to ECM or ECM is faulty.