DTC 15

Fig. 039 - Wiring Diagram for Code 15 Open Coolant Sensor Circuit. VIN C:

CODE 15, COOLANT SENSOR CIRCUIT OPEN

The Coolant Temperature Sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage on CKT 410 to the sensor. When the engine is cold the sensor (Thermistor) resistance is high, therefore the ECM will set a high signal voltage.
As the engine warms, the sensor resistance becomes less, and the voltage drops. At normal engine operating temperature, the voltage will measure about 1 to 1.5 volts at the ECM terminal 17.
Coolant temperature is one of the inputs used to control:
a. Fuel Delivery.
b. Air Management (A.I.R.)
Trouble Code 15 means the ECM has seen the resistance of the Coolant Sensor Circuit too high as follows:
a. High resistance (Cold Engine Temperature)
b. Or over 5.00 volts at ECM Terminal "17" (caused by open wire)
c. For a time longer than 10 minutes
This could cause detonation on a warm engine due to too much spark advance or poor driveability due to wrong fuel control.

Fig. 038 - Chart - Code 15 Open Coolant Sensor Circuit.:

1. Checks system by introducing a large air leak to the engine and see if this will cause the dwell to decrease and to see if problem is still present.
Normal reading is a decrease in dwell. Somewhere around 10°.
2. Checks to see if the fault is the coolant sensor orlack of voltage to the coolant sensor.
Normally you should have 5 volts across the coolant sensor connector terminals.
3. Determines whether the low voltage at the sensor connector is due to opens in the coolant sensor wires or good terminal contact.
Normal voltage should be about 5V from ECM Terminals "17" to "8".
4. Checks resistance of the coolant sensor. If the resistance is within 1000 ohms specifications, coolant sensor is not faulty; therefore, check for corrosion at the connector or low coolant level.