Code 15, ECT Sensor Circuit, High Temperature Indicated: Notes

Engine Coolant Temperature (ECT) sensor is a thermistor in series with a fixed resistor in ECM. ECM applies 5 volts to sensor. ECM monitors voltage across ECT sensor and converts it into a temperature reading. When engine is cold, ECT sensor resistance is high. When engine is warm, ECT sensor resistance is low. Therefore, when engine is cold, ECM receives a high voltage input and when engine is warm, ECM receives a low voltage input.

Code 15 will set when voltage input at ECM indicates 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 its wiring are okay and ECT sensor is faulty. If Code 15 resets, ECT sensor is okay and wiring to ECM or ECM is faulty.