DTC 15

Code 15 - Coolant Temp. Sensor (Low Temp. Indicated):

Wiring Diagram for Coolant Temp. Sensor:

CODE 15 - COOLANT TEMPERATURE SENSOR CIRCUIT (LOW TEMPERATURE INDICATED)

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~C to 95~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~C (-22~F), for 3 seconds

^ No Code 23

^ Manifold Air Temperature (MAT) temperature indicated above -25~C (-13~F)

^ OR

^ Engine running longer than 1 minute

^ Signal voltage indicates a coolant temp. less than -30~C (-22~F) for 3 seconds.

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

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~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 intermittents in Diagnosis By Symptoms - No Trouble Codes Stored.