DTC 15

Code 15 Chart:

Wiring Diagram For Coolant Temperature Sensor:

CIRCUIT DESCRIPTION:

The Coolant Temperature Sensor (CTS) is a thermistor that controls the signal voltage to the ECM. The ECM applies a voltage on circuit 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 ECM terminal "B8." The coolant temperature sensor is one of the inputs used to control the following:

1. Fuel Delivery
2. Electronic Spark Timing (EST)
3. Cooling Fan operation
4. Torque Converter Clutch (TCC)
5. Idle Air Control (IAC)


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

1. This checks to see if a code was set as a result of a hard failure or an intermittent problem.
A Code 15 will set if:
a. Signal voltage indicates a coolant temperature below -37°C (-35°F) for 60 seconds.

2. This test stimulates conditions for a Code 14. If the ECM recognizes the grounded circuit (low voltage) and displays a high temperature, the ECM and wiring are OK.

3. This test will determine if there is a wiring problem or a faulty ECM. If circuit 452 is open, there also may be a Code 21 stored in the ECM.


DIAGNOSTIC AIDS:

1. A Code 15 will set if circuits 410 or 452 are open. If a code 15 sets, the ECM will energize the cooling fan.
2. A "Scan" tool displays engine temp. in degrees centigrade. After engine the is started, the temperature should rise steadily to about 90°C then stabilize when thermostat opens.
3. If the engine has been allowed to cool to ambient temperature, coolant temperature and Manifold Air Temperature (MAT) or Intake Air Temperature (IAT) may be checked with a "Scan" tool. The readings should be close to each other.
4. The "Temperature to Resistance Value" scale above can 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 driveability complaints.
5. If a Code 15 is intermittent, see DIAGNOSIS BY SYMPTOM.