Code 15: Coolant Temp Sensor Signal Volt High: Notes

At operating temperature, voltage will measure about 1-2 volts at ECM terminal.

NOTE: Test numbers refer to test numbers on diagnostic chart. The "Scan" tester reads engine temperature in degrees centigrade.

Code 15 will set if the monitored voltage indicates a coolant temperature less than -36°F (-38°C) for at least 4 seconds with engine running.
This test simulates a Code 14. If the ECM recognizes the low signal voltage (high temperature) and "Scan" tester reads 140°C, the ECM and wiring are okay.
This test determines if circuit No. 410 is open. Using a digital volt-ohmmeter, there should be 5 volts present at sensor connector. If Code 15 is set, the ECM uses a default coolant value of about 120°F (49°C). However, the "Scan" tester will read the actual temperature indicated by the sensor.