DTC 15

Code Chart 15:

TPS 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) the voltage 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 a 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 scan tool displays 140°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.

NOTE: If DTC 15 is set, the ECM will use a fail-soft engine coolant temperature of 49°C (120°F) for fuel control. The scan tool will continue to display actual sensor value.

DIAGNOSTIC AIDS:
"Scan" tool displays engine temperature in degrees Celsius. After engine is started, the temperature should rise steadily to about 90°C, and then stabilize when 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 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, "Scan" coolant temperature while moving related connectors and wiring harness. If the failure is induced, the "coolant temperature" 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 coolant 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 DTC 15.