With 4L80E Automatic Transmission

Coolant Temperature Sensor Circuit Code 15:

Coolant Temperature Sensor Circuit:

Circuit Description:
The Coolant Temperature Sensor (CTS) 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:
Number(s) below refer to circled number(s) 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 14. If the PCM recognizes the low signal voltage (high temperature), and the Tech 1 "Scan" tool 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 Tech 1 "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 CKTs 410 or 452 will result in a Code 15.

- Intermittent Malfunctions

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