Page 6E2-46 DOHC Code 14B - C.T.S. Low Temp. Indicated

Fig. 6E2-31:

6E2-46 DRIVEABILITY AND EMISSIONS (DOHC)

CODE 14B

COOLANT TEMPERATURE SENSOR CIRCUIT (LOW TEMPERATURE INDICATED)


Circuit Description:

The Coolant Temperature Sensor uses a thermistor to control the signal voltage at 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 "A-11". Coolant temperature is one of the inputs used to control:
^ Fuel delivery
^ Engine Spark Timing (EST)
^ Idle (IAC)

Test Description:

Numbers below refer to circled numbers on the diagnostic charts.
(1) Checks to see if code was set as result of hard failure or intermittent condition.
Code 14B will set if:
^ The engine has been running for 4.25 minutes.
^ Signal Voltage indicates a coolant temperature below -30~C (-22~F).
(2) This test simulates conditions for Code 14A. 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.

Diagnostic Aids:

A "Scan" tool reads engine temperature in degrees centigrade. After the engine is started, the temperature should rise steadily to about 90~C, then stabilize, when the thermostat opens. If the engine has been allowed to cool to an ambient temperature (overnight), coolant and MAT temperatures may be checked with a "Scan" tool and should read close to each other. A Code 14B will result if CKT 410 or CKT 452 are open. If Code 14B is intermittent, refer to Section "B".