Standard Emissions

CODE 15 COOLANT TEMPERATURE SENSOR (HIGH TEMP. INDICATED)

ECT System Check:

ECT Wiring 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 sensor. The ECM monitors the voltage across the coolant temperature 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) 15 will set if the following condition is met for at least 3 seconds; Voltage input at the ECM indicates a coolant temperature above 136°C (276°F).

TEST DESCRIPTION
The number below refers to the circled number on the diagnostic chart.

1. This test simulates DTC 14. If the ECM stores DTC 14, the ECM and its wiring are OK and the ECT sensor is faulty. If DTC 15 resets, the ECT sensor is OK and the wiring to the ECM or the ECM is faulty.

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

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