Powertrain Control Module PCM

DTC 15 Engine Coolant Temp Sensor Diagnosis - Low Temp Indicated:

Temp Sensor Circuit Wiring:

Circuit Description:
The Engine Coolant Temperature (ECT) sensor is a thermistor that controls 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 a 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.

DTC 15 Will Set When: Signal voltage indicates an engine coolant temperature less than -33° C (-2"° F) for 2 seconds.

Action Taken (PCM will default to): The Malfunction Indicator Lamp (MIL) will illuminate, and transmission TCC will apply early.

DTC 15 Will Clear When: Conditions for fault are no longer present and Tech 1 "clear DTCs" function is used or 50 ignition switch keycycles have passed with no further faults or ignition switch is turned "OFF" and ECM B fuse is removed for 10 seconds.

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

1. This test verifies coolant temperature display.

2. This test simulates a DTC 14. If the PCM recognizes the low signal voltage (high temperature), and the Tech 1 scan tool reads 130° C or above, 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 when measured with a J 39200.

Diagnostic Aids: A Tech 1 scan tool reads engine temperature in degrees centigrade and fahrenheit. After engine is started, the temperature should rise steadily to about 90° C (194° F) then stabilize when thermostat opens.

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

Refer to DIAGNOSIS BY SYMPTOMS/ INTERMITTENTS - Intermittent Malfunctions.

The "Temperature To Resistance Value" scale in the chart may be used to test the coolant sensor at various temperature levels to evaluate the possibility of a "skewed" (mis-scaled) sensor. A "skewed" sensor could result in poor driveability complaints.