DTC CI-121: Engine Coolant Temperature (ECT) Signal Faulty
- This DTC will set if control module receives a signal from ECT sensor which corresponds to a temperature less than -49°F (-45°C) or more than 302°F (150°C). The coolant temperature gauge may permanently read low temperature.
- To correct this problem, turn ignition on. Read fuel and ignition system DTCs. If ECT DTC is stored, repair that DTC. See ENGINE PERFORMANCE. If no ECT DTC is stored, go to next step.
- Using scan tool, perform status check. Go into scrolling values and read engine coolant temperature. If scan tool displays -40°F (40°C), go to next step. If scan tool does not display -40°F (40°C), repair open Green/Gray wire between instrument cluster connector terminal A26 and Engine Control Module (ECM) terminal B23. See Figure.
- Turn ignition off. Connect breakout box to ECM. Disconnect ECM from vehicle. Turn ignition on. Measure voltage between breakout box terminals B23 and B28. If voltage is less than 6 volts, repair open Green/Gray wire between instrument cluster connector terminal A26 and Engine Control Module (ECM) terminal B23. If voltage is more than 6 volts, repair short to voltage in Green/Gray wire between instrument cluster connector terminal A26 and ECM terminal B23. If voltage is 6 volts, check for resistance or corrosion in ECM connector terminals and repair as necessary. Retest system.