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

LOW 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 Engine Coolant Temperature (ECT) Sensor signal voltage.

As the Engine warms, the Sensor resistance becomes less, and the ECT Sensor signal voltage drops. At normal Engine operating temperature, the voltage will measure about 1.5 to 2.0 volts at the ECM terminal "D12." ECT is one of the inputs used to control:
- 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 14B will set if:
- The Engine has been running at least for 3 minutes.
- ECT Sensor signal voltage indicates a ECT above -35°C (-31°F) for 30 seconds.

2. This test simulates conditions for DTC 14A. If the ECM recognizes the grounded circuit (low voltage), and displays a high temperature, the ECM and wiring are OK.
3. This test will determine if there is a wiring problem or a faulty ECM.

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 and Intake Air Temperature may be checked with a "Scan Tool" and should read close to each other.
- A DTC 14B will result if GRY/BLK wire GRY are open.
- If DTC 14B is intermittent, refer to Diagnosis by Symptom. Symptom Related Diagnostic Procedures