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Code Chart 14:

CTS Circuit:

CIRCUIT DESCRIPTION:
The Coolant Temperature Sensor (CTS) uses a thermistor to control 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, the voltage will measure about 1.5 to 2.0 volts at ECM terminal "B4." Coolant temperature is one of the inputs used to control the following:

^ Fuel Delivery.
^ Electronic Spark Timing (EST).
^ Cooling Fan operation.
^ Torque Converter Clutch (TCC).
^ Idle Air Control (IAC).

A second thermistor within the CTS provides a signal to the coolant temperature gauge located in the instrument panel.

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

1. A Code 14 will set if:

^ Engine has been running for 2 minutes.
^ Signal voltage indicates a coolant temperature below -34°C (-30°F).
OR
^ Signal voltage indicates a coolant temperature above 143°C (289°F) for three seconds.

2. 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 CKT 452 is open, there may also be other codes stored.

DIAGNOSTIC AIDS:

^ A "Scan" tool displays engine temperature in degrees Celsius. After engine is started, the temperature should rise steadily to about 90°C (194°F) then stabilize when thermostat opens.
^ If the engine has been allowed to cool to ambient temperature, coolant temperature and Intake Air Temperature (IAT) may be checked with a "Scan" tool. The readings should be close to each other.
^ When a Code 14 is set, the ECM will energize the cooling fan.
^ If Code 14 is intermittent, Testing and Inspection