Code Definitions
- DTC P0116: Engine Coolant Temperature Circuit Range/Performance Fault
- DTC P0125: Insufficient Coolant Temperature For Closed Loop Fuel Control
Note. For information on engine immobilizer system, see COMPUTERIZED ENGINE CONTROLS in THEORY & OPERATION article.
| CAUTION | If ECM replacement is instructed in following testing, always ensure ECM harness connector and ground circuit are okay. If either are suspect, repair and repeat testing to confirm ECM malfunction. If ECM is replaced, ECM must be programmed with proper ignition key code for engine immobilizer system. For programming procedures, see COMPUTER RELEARN PROCEDURES - LEXUS article. |
Circuit Description
The ECT sensor is a thermistor that monitors coolant temperature. DTC is set when after engine has been running for predetermined amount of time, sensor value is out of specified range. Possible causes are
- Faulty ECT sensor.
- Engine cooling system fault.
Diagnostic Aids
After confirming DTC, use scan tool to access CURRENT DATA to confirm engine coolant temperature. If temperature displayed on scan tool is -40°F (-40°C), ECT sensor circuit may be open. If temperature displayed on scan tool is 284°F (140°C) or more, ECT sensor circuit may be shorted. Using scan tool, read freeze frame data. Freeze frame records engine conditions when malfunction is detected.