DTC 15

Chart - Code 15 Coolant Sensor Circuit (Signal Voltage High):

Wiring Diagram for Coolant Sensor Circuit.:

CODE 15 - COOLANT TEMPERATURE SENSOR (LOW TEMPERATURE INDICATED) 2.8L (PORT)


Circuit Description:


The coolant temperature sensor uses a thermistor to control the signal voltage to the Electronic Control Module (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 see high signal voltage. As the engine warms, the sensor resistance becomes less, and the voltage drops. At normal engine operating temperature (85 degrees C to 95 degrees C) the voltage will measure about 1.5 to 2.0 volts at the ECM.


Test Description: Numbers below refer to circled numbers on the diagnostic chart.
1. Code 15 will set if:

-Ignition "ON", engine not running
-Coolant temperature less than -30 degrees C (-22 degrees F), for 3 seconds
-No Code 23
-Manifold Air Temperature (MAT) temperature indicated above -25 degrees C (-13 degrees F)
-Engine running longer than 1 minute
-Signal voltage indicates a coolant temp. less than -30 degrees C (-22 degrees F) for 3 seconds.

2. This test simulates a Code 14. If the ECM recognizes the low signal voltage, (high temp.) and the "Scan" reads 130 degrees C or above, the ECM and wiring are 0K.

3. This test will determine if CKT 410 is open. There should be 5 volts present at sensor connector if measured with a Digital Volt Meter (DVM).


Diagnostic Aids:

A "Scan" tool reads engine temperature in degrees centigrade. After engine is started the temperature should rise steadily to about 90 degrees C then stabilize when thermostat opens. If Code 21 is also set, check CKT 452 for faulty wiring or connections, Check terminals at sensor for good contact. Refer to "DIAGNOSIS BY SYMPTOMS - NO TROUBLE CODE STORED".