With TBI

Code 14 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 sense a 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 14 will set if:
a. Signal voltage indicates a coolant temperature above 135°C (275°F) for three seconds.

2. This test stimulates conditions for a code 15. If the ECM recognizes the open circuit (high voltage) and displays a low temperature, the ECM and wiring are OK.


DIAGNOSTIC AIDS:

1. A Code 14 will set if circuit 410 is shorted to ground. Check harness routing for a potential short to ground in circuit 410. If a code 14 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 14 is intermittent, see DIAGNOSIS BY SYMPTOM.