Code 14A - Engine Coolant Temperature (ECT) Sensor Circuit

HIGH TEMPERATURE INDICATED




Circuit Description
The Engine Coolant Temperature Sensor uses a Thermistor to control the signal voltage to the Engine Control Module (ECM). The ECM applies a reference voltage on GRY/BLK wire to the Sensor. When the Engine is cold, the Sensor (Thermistor) resistance is high. The ECM will then sense a high signal voltage.

As the Engine warms, the Sensor resistance decreases, and the voltage drops. At normal Engine operating temperature, the voltage will measure about 1.5 to 2.0 volts at the ECM Terminal "D12." Engine Coolant temperature is one of the inputs used to control the following:
- Fuel Delivery.
- Ignition Control.
- Idle Air Control.




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

1. Checks to see if Diagnostic Trouble Code (DTC) was set as result of hard failure or intermittent condition. DTC 14A will set if:
- The Engine has been running for at least 3 minutes.
- Signal Voltage indicates a Engine Coolant temperature above 150°C (302°F).

2. This test simulates conditions for DTC 14B. If the ECM recognizes the open circuit (high voltage), and displays a low temperature, the ECM and wiring are OK.

Diagnostic Aids
- A "Scan Tool" reads Engine temperature in degrees Celsius.
- After the Engine is started, the temperature should rise steadily to about 90°C, then stabilize, when the Thermostat opens.
- If the Engine has been allowed to cool to an ambient temperature (overnight), Engine Coolant Temperature (ECT) and Intake Air Temperature (IAT) may be checked with a "Scan Tool" and should read close to each other.
- A DTC 14A will result if GRY/BLK wire is shorted to ground.
- If DTC 14A is intermittent, refer to Diagnosis by Symptom. Symptom Related Diagnostic Procedures