Powertrain Controls - ECM/PCM

Code 15 Diagnostic Chart:

Engine Coolant Temperature (ECT) Sensor Wiring Schematic:

CIRCUIT DESCRIPTION
The Engine Coolant Temperature (ECT) sensor uses a thermistor to control the signal voltage at the Powertrain Control Module (PCM). The PCM applies a voltage on CKT 410 to the sensor. When the engine is cold the sensor (thermistor) resistance is high, therefore PCM terminal "PC10" voltage will be high. As the engine warms, the sensor resistance becomes less, and the voltage drops. At normal engine operating temperature, the voltage will measure about 1.5 to 2.0 volts at PCM terminal "PC1O".

Engine coolant temperature is one of the inputs used to control:
^ Fuel delivery.
^ Torque Convertor Clutch (TCC).
^ Ignition Control (IC).
^ Evaporative Emission (EVAP) canister purge solenoid valve.
^ Idle Air Control (IAC).
^ Electric coolant fan.

DTC 15 WILL SET WHEN
Signal voltage indicates an engine coolant temperature less than -39°C (-38°F) for 60 seconds.

ACTION TAKEN (PCM WILL DEFAULT TO)
Malfunction Indicator Lamp (MIL) illuminates. PCM will default to 92°C (197°F) for engine coolant temperature.

NOTE: Tech 1 scan tool will not show defaulted value.

TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This step checks to see if DTC 15 was set as a result of a hard or intermittent condition.
2. This test simulates a DTC 14. If the PCM senses the low signal voltage (high temperature) and the scan tool reads 130°C (266°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 DVM.

DIAGNOSTIC AIDS
^ A Tech 1 scan tool displays engine coolant temperature in degrees celsius. After the engine is started the temperature should rise steadily to about 90°C (195°F), and then stabilize when the thermostat opens. It is normal for engine coolant temperature to fluctuate slightly around 95°C (203°F).
^ A faulty connection, or an open in CKT 410 or CKT 452 can result in a DTC 15.
^ DTCs 15, 21 and 66 stored at the same time could be the result of an open CKT 452.
^ The "Temperature vs. Resistance Value", scale shown in the diagnostic chart, may be used to test the sensor at various temperatures to evaluate the possibility of a "shifted" (mis-scaled) sensor. A "shifted" sensor could result in poor driveability complaints.
^ Refer to "DIAGNOSIS BY SYMPTOM/INTERMITTENTS" Testing and Inspection