CIRCUIT DESCRIPTION:
The Coolant Temperature Sensor (CTS) uses a thermistor to control the signal voltage to the ECM The ECM applies a voltage on CKT 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, the voltage will measure about 1.5 to 2.0 volts at the ECM terminal "GE 16."

Coolant temperature is one of the inputs used to control:

• Fuel Delivery
• Torque Converter Clutch (TCC)
• CAC Pump
• Idle Air Control (IAC)

Coolant Sensor
Temperature vs Resistance (Approx)
Deg. F	Deg. C	Ohms
210	100	185
160	70	450
100	38	1,800
70	20	3,400
40	4	7,500
20	-7	13,500
0	-18	25,000
-40	-40	100,700

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

1. Checks to see if code was set as result of hard failure or intermittent condition. Code 14 will set if:
   • Engine has been running for more than 10 seconds.
   • Signal voltage indicates a coolant temperature above 135'C (275'F) for 3 seconds.
2. This test simulates 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:
A "Scan" tool reads engine temperature in degrees centigrade. After the engine is started, the temperature should rise steadily to about 90', then stabilize, when the thermostat opens. If the engine has been allowed to cool to an ambient temperature (overnight), coolant and MAT temperature may be checked with a "Scan" tool and should read close to each other. When a Code 14 is set, the ECM will turn "ON" the engine cooling fan. A Code 14 will result if CKT 410 is shorted to ground. If Code 14 is intermittent, refer to the Intermittemts page.