Powertrain Controls - ECM/PCM

Trouble Code 15 Chart:

Engine Coolant Temperature (ECT) Wiring Schematic:

CIRCUIT DESCRIPTION
The Engine Coolant Temperature (ECT) sensor is a thermistor used to modulate a 5 volt reference signal applied to Circuit (CKT) 410. When the engine is cold, the sensor resistance is high which causes the voltage at pin "A31" to remain high. The Powertrain Control Module (PCM) calculates a high signal voltage as a low engine coolant temperature.

As the engine warms, the sensor resistance drops and voltage at the PCM terminal drops. At normal engine operating temperature, the voltage will measure approximately 1.75 volts on CKT 410.

Engine coolant temperature is one of the inputs used to control:
^ Fuel delivery.
^ Idle air control.
^ Purge control.
^ Cooling fan operation.
^ Ignition control.
^ Torque Converter Clutch (TCC) operation.
^ EGR operation.

DIAGNOSTIC TROUBLE CODE (DTC) 15 WILL SET WHEN
A DTC 15 will set when the ECT sensor indicates an engine coolant temperature less than -38°C (-37°F) for more than 2 seconds.

ACTION TAKEN (PCM WILL DEFAULT TO)
The PCM will use a default value of 90°C (194°F) for fuel delivery calculations. The cooling fans will be enabled and the MIL will become illuminated.

DTC 15 WILL CLEAR WHEN
A current DTC 15 will clear when the low temperature failure is no longer detected [temperature rises above -38°C (-37°F) threshold]. A History DTC 15 will clear after 50 consecutive ignition key cycles without a current DTC 15 being stored.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This is to verify that the temperature fault is not intermittent.
2. This test simulates a DTC 14. If the PCM recognizes the low signal voltage (high temperature), and the Tech 1 scan tool reads 135°C (275°F), 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 DVOM.

DIAGNOSTIC AIDS
^ A Tech 1 scan tool reads engine temperature in degrees centigrade. After the engine is started, the temperature should rise steadily to about 90°C (194°F) then stabilize when the thermostat opens. CKT 410 is routed from the PCM through an injector harness connector, and then to the ECT sensor.
^ A faulty connection, or an open in CKT 410 or 452 will result in a DTC 15.
^ The "Temperature to Resistance Value" scale in the chart may be used to test the engine 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.
^ See Intermittents. Under Diagnosis By Symptom.