DTC 15

DTC 15 - Coolant Temperature (ECT) Sensor Circuit (Low Temp):

Coolant Temperature Sensor Wiring Circuit:

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 (85°C to 100°C/185°F to 212°F), the ECT signal will measure about 1.5 to 2.0 volts.

DTC 15 will set if:
^ Engine run time 2 seconds or more.
^ ECT sensor voltage indicates engine coolant temperature less than -38°C (-36°F) for at least .4 second.

Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

1. This will determine if the ECT sensor is indicating a low temperature to the ECM.
2. This test simulates DTC 14. If the ECM recognizes the low signal voltage (high temperature) and the Tech 1 displays 140°C (284°F), the ECM and wiring are OK.
3. This test will determine if CKT 410 is open. There should be 5 volts present at ECT sensor connector if measured with a DVM.

NOTICE: If DTC 15 is set, the ECM will use a fail-soft engine coolant temperature of 32°C (120°F) for fuel control. The Tech 1 will continue to display the actual sensor value.

Diagnostic Aids:

The Tech 1 reads engine coolant temperature in degrees. After the engine is started, engine coolant temperature should rise steadily to about 90°C (194°F) then stabilize when thermostat opens.

An intermittent may be caused by a poor connection or a wire broken inside the insulation.

Check for:
^ Poor Connection or Damaged Harness. Inspect ECM harness connectors for backed out terminal "YE16" or "BB6", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
^ Intermittent Test. If connections and harness check OK, monitor engine coolant temperature while moving related connectors and wiring harness. If the failure is induced, the display will change. This may help to isolate the location of the malfunction.
^ Shifted Sensor. The "Temperature To Resistance Value" scale may be used to test the ECT sensor at various temperature levels to evaluate the possibility of a "shifted" (mis-scaled) sensor which may result in driveability complaints.

A faulty connection, or an open in CKT 410 or 452 will result in DTC 15.