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CODE 14 COOLANT TEMPERATURE SENSOR CIRCUIT

Diagnostic Chart:

ECT Sensor Schematic:

CIRCUIT DESCRIPTION
The Engine Coolant Temperature (ECT) sensor is a thermistor (a variable resistor that changes along with coolant temperature) in series with a fixed resistor in the Engine Control Module (ECM). The ECM applies 5.0 volts to the ECT sensor. The ECM monitors the voltage across the ECT sensor and converts it into a temperature reading. When the engine is cold, the sensor resistance is high, therefore, the ECM will see high signal voltage. As the engine warms, the sensor resistance becomes less, and the ECM will read a low voltage input.

Diagnostic Trouble Code (DTC) 14 will set if the following condition is met for at least 3 seconds: Voltage input at the ECM indicates ECT below -48°C (-54°F).

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

1. This test simulates a DTC 15. If the ECM stores a DTC 15, the ECM and wiring are OK and the ECT sensor is faulty. If DTC 14 repeats, the ECT sensor is OK and the wiring to the ECM or the ECM if faulty.
2. This test determines whether there is an open in the GRY/WHT or LT GRN/BLK wires, a short to B+ in the GRY/WHT wire or a faulty ECM.

DIAGNOSTIC AIDS
After engine is started the temperature should rise steadily to about 95°C (203°F) then stabilize when thermostat opens.

DTCs 14, 23 and 32 stored at the same time could be the result of an open LT GRN/BLK sensor ground wire.

When replacing the ECT sensor, the "Temperature to Resistance Value" scale on the diagnostic chart may be used to test the ECT sensor at various temperature levels to evaluate the possibility of a "shifted" (mis-scaled) sensor. A "shifted" sensor could result in poor driveability complaints.