Powertrain Controls - ECM/PCM

Code 14 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 14 WILL SET WHEN
^ Signal voltage indicates an engine coolant temperature above about 140°C (285°F).
^ Engine running longer than 128 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 14 was set as a result of a hard failure or intermittent condition.
2. This test will determine if CKT 410 is shorted to ground which will cause the conditions for DTC 14.

DIAGNOSTIC AIDS
^ Check harness routing for a potential short to ground in CKT 410. A Tech 1 scan tool displays engine coolant temperature in degrees celsius. After engine is started, the temperature should rise steadily to about 90°C (195°F), and then stabilize when thermostat opens. Refer to "DIAGNOSIS BY SYMPTOM/INTERMITTENTS" Testing and Inspection
^ Verify that engine is not overheating and has not been subjected to conditions which could create an overheating condition (i.e. overload, trailer towing, hilly terrain, heavy stop and go traffic, etc.). 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.