DTC 15

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

TPS Sensor, ECT Sensor, IAT Sensor Wiring Circuit:

Circuit Description:

The Engine Coolant Temperature (ECT) sensor uses a thermistor to control the signal voltage to the PCM. The PCM applies a voltage on CKT 410 to the sensor. When the engine is cold the sensor (thermistor) resistance is high; therefore, the PCM will see high signal voltage.

As the engine warms, the sensor resistance becomes less, and the voltage drops. At normal engine operating temperature (8500 to 9500), the voltage will measure about 1.5 to 2.0 volts.

DTC 15 will set if:
^ Engine has been running for over 2 seconds.
^ ECT sensor signal voltage indicates an engine coolant temperature less than -39°C (-36°F) for at least .4 second.

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

1. Determines if conditions necessary to set DTC 15 exist.
2. This test simulates a DTC 14. If the PCM recognizes the low signal voltage, (high temperature) and the scan reads 130°C (266°F) or more, the PCM and wiring are OK.
3. This test will determine if CKT 410 is open. There should be 5 volts present at sensor connector if measured with a DVM.

Diagnostic Aids:

A Tech I displays engine temperature in degrees. After engine is started the temperature should rise steadily to about 90°C (194°F) then stabilize when the thermostat opens.

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

Check for:

^ Poor Connection or Damaged Harness - Inspect PCM harness connectors for backed out terminal "BB9", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
^ Intermittent Test - With Tech 1, 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 engine coolant temperature 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 CKTs 410 or 452 will result in a DTC 15.