Powertrain Control Module PCM

Diagnostic Trouble Code 15:

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 ECT signal circuit 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 (185°F to 203°F) the voltage will measure about 1.5 to 2.0 volts.

DTC 15 WILL SET WHEN
Signal voltage indicates 4.9 volts or an engine coolant temperature less than -33°C (-27°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 battery feed voltage 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 (266°F) 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 Symptom / 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.