With 4L80 Automatic Transmission

Code 15 - Coolant Temperature Sensor Circuit:

Wiring Diagram For Code 15 Coolant Temperature Sensor Circuit:

CODE 15 - COOLANT TEMPERATURE SENSOR CIRCUIT

CIRCUIT DESCRIPTION:

The coolant temperature sensor is a thermistor that controls the signal voltage to the PCM. The PCM applies a voltage on CKT 410 to the sensor. When the engine is cold, the sensor (thermistor) resistance is high, therefore the PCM 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.


TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. Code 15 will set if:

^ Signal voltage indicates a coolant temperature less than -33~C (-27~F) for 30 seconds.

2. This test simulates a Code 15. If the PCM recognizes the low signal voltage, (high temp.) and the "Scan" reads 130~C or above, the PCM 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 DVOM.


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.

A faulty connection, or an open in CKT 410 or 452 will results in a Code 15.

The "Temperature To Resistance Value" scale above may be used to test the coolant sensor at various temperature levels to evaluate the possibility of a "slewed" (mis-scaled) sensor. A "slewed" sensor could result in poor driveability complaints.

DIAGNOSIS BY SYMPTOM NO TROUBLE CODES STORED.