Federal Emissions

Code 14 Diagnostic Chart:

Coolant Temperature Sensor (CTS) Circuit Diagram:

CIRCUIT DESCRIPTION
The Engine Coolant Temperature (ECT) sensor 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 "C16"

Engine coolant temperature is one of the inputs used to control:
^ Fuel delivery.
^ EVAP canister purge.
^ Ignition Control (IC).
^ Exhaust Gas Recirculation (EGR).
^ Idle Air Control (IAC).
^ Cooling fan operation.
^ Torque Converter Clutch (TCC).

TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. DTC 14 will set if:
^ Signal voltage indicates engine coolant temperature is above 135°C (270°F).
^ Engine running longer than 20 seconds.

2. This test will determine if CKT 410 is shorted to ground which will cause the conditions for DTC 14.


DIAGNOSTIC AIDS:

^ Check harness routing for a potential short to ground in CKT 410. Circuit is routed from the ECM to a mini harness, and then to the Engine Coolant Temperature (ECT) sensor.

^ Tech 1 scan tool displays engine coolant temperature in degrees centigrade. After the engine is started the temperature should rise steadily to about 90°C (194°F) then stabilize when the thermostat opens.

^ Verify that engine is not overheating and has not been subjected to conditions which could create an overheating condition (i.e. overload, trailer towing, hilly terrain, heavy stop and go traffic, etc.). The "Temperature To Resistance Value" scale in the chart may be used to test the engine coolant sensor at various temperature levels to evaluate the possibility of a "shifted" (mis-scaled) sensor. A "shifted" sensor could result in poor driveability complaints.