Powertrain Controls - ECM/PCM

DTC 14 Engine Coolant Temperature (ECT) Sensor Circuit (High Temperature Indicated):

Engine Coolant Temperature (ECT) Sensor Circuit:

CIRCUIT DESCRIPTION
The Engine Coolant Temperature (ECT) sensor uses a thermistor to control the signal voltage to the Powertrain Control Module (PCM). The PCM supplies a 5 volt reference and a ground to the sensor. When the engine is cold the sensor (thermistor) resistance is high, therefore PCM terminal voltage will be high.
As the engine warms, the sensor resistance decreases, and the voltage drops. At normal engine operating temperature, ECT sensor voltage should be between 1.5 to 2.0 volts.

Engine coolant temperature is one of the inputs used to control:

^ Fuel delivery.
^ Ignition Control (IC).
^ Idle Air Control (IAC).
^ Torque Convertor Clutch (TCC).
^ Evaporative (EVAP) canister purge valve.
^ Electric cooling fan.

DIAGNOSTIC TROUBLE CODE (DTC) 15 WILL SET WHEN
^ ECT signal voltage indicates engine coolant temperature is less than -39°C (-38°F).
^ Engine run time is greater than 60 seconds.

ACTION TAKEN (PCM WILL DEFAULT TO)
The Malfunction Indicator Lamp (MIL) will illuminate, and the PCM will default to 92°C for engine coolant temperature (Tech 1 scan tool will not display defaulted value) and the cooling fan will enable.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. This checks if DTC 15 was set as a result of a hard or intermittent condition.
2. This simulates a DTC 14. If tile PCM senses the low signal voltage (high temperature) and the scan tool reads 130°C, the PCM and wiring are OK.
3. This will determine if CKT 410 is open. There should be 5 volts present at sensor connector when measured with a DVM.

DIAGNOSTIC AIDS
^ After the engine is started the temperature should rise steadily to about 90°C, and then stabilize when the thermostat opens. It is normal for engine coolant temperature to fluctuate slightly around 95°C.
^ A faulty connection, an open or short to voltage in CKT 410, can result in a DTC 15.
^ If DTCs 15, 33 and 66 are set at the same time it could be the result of an open in CKT 469.
^ The "Temperature to Resistance Value" scale to the right may be used to test the sensor at various temperature levels to evaluate the possibility of a "shifted" (mis-scaled) sensor. A shifted sensor could result in poor driveabiliy.
^ Refer to "Intermittents," in Diagnosis by Symptom.