DTC 15

Code Chart 15:

ECT 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 95°C) the voltage will measure about 1.5 to 2.0 volts at the ECM.

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

1. DTC 15 will set if:

^ Signal voltage indicates an open circuit (a coolant temperature less than -39°C) for 1 second at normal ambient temperature.

2. This test simulates a DTC 14. If the ECM recognizes the low signal voltage, (high temperature) and the scan reads 135°C, the ECM 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 1 scan tool reads engine temperature in degrees centigrade. After engine is started the temperature should rise steadily to about 90°C then stabilize when thermostat opens.

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

If DTC 21 or 23 is also set, check CKT 452 for faulty wiring or connections. Check terminals at sensor for good contact. - Intermittent Malfunctions