Part 2 of 2

Code Chart 14:

ECT Circuit:

CIRCUIT DESCRIPTION:
The Engine Coolant Temperature (ECT) sensor utilizes a thermistor to control the signal voltage to the Engine Control Module (ECM). The ECM applies a reference voltage on CKT 410 to the sensor. When the engine is cold, the sensor (thermistor) resistance is high. The ECM will then sense a high signal voltage.

As the engine warms up, the sensor resistance decreases 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:

^ Cooling fan.
^ Fuel delivery.
^ Ignition Control (IC).
^ Idle Air Control (IAC).
^ Torque Converter Clutch (TCC).

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

1. Checks to see if a DTC was set as a result of hard failure or intermittent condition.

2. 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 should display engine coolant temperature in degrees Celsius.

After the engine is started, the temperature should rise steadily to about 90°C (194°F) then stabilize when the thermostat opens.

If the engine has been allowed to cool to an ambient temperature (overnight), Engine Coolant Temperature (ECT) and Intake Air Temperature (IAT) may be checked with a scan tool and should read close to each other.

When a DTC 14 is set, the ECM will turn "ON" the engine cooling fan.

^ If DTC 14 is intermittent or a "Hard Start" symptom is present, check engine coolant temperature with a scan tool on a cool engine. Temperature displayed should be within 5 degrees of the ambient. If not, check the ECT sensor using the "Diagnostic Aids" on the next part. If sensor is OK, check connections.