Code 15 - Coolant Sensor Circuit Open
The Coolant Temperature Sensor uses a thermistor to control the signal to the ECM. The ECM applies a voltage on circuit No. 410 to sensor. When engine is cold, sensor (Thermistor) resistance is high. Therefore the ECM will set a high signal voltage. As the engine warms, sensor resistance becomes less, and voltage drops. At normal engine operating temperature, voltage will measure about 1-1.5 volts at ECM terminal No. 17. Coolant temperature is used to control fuel delivery and air management. Code 15 means the ECM has seen resistance of the coolant sensor circuit too high (cold engine temperature), or over 5 volts at ECM terminal No. 17 (caused by open wire) for longer than 10 minutes. This condition can cause detonation and poor driveability.
- This test checks if problem is still present by introducing a large air leak. Normal response is for dwell to decrease to around 10 degrees.
- This test checks if fault is with coolant sensor or is a lack of voltage to coolant sensor. Normal reading is 5 volts across coolant sensor.
- Determines whether the low voltage at sensor connector is due to open in the coolant sensor wires or contacts. Normal reading is about 5 volts from ECM terminals No. 17 to 8.
- This test checks resistance of coolant sensor. If resistance is less than 1000 ohms, coolant sensor is not faulty. Check for corrosion at connector or low coolant level.