ECT - Engine Temperature sensor is simply a negative temperature coefficient thermistor that changes in resistance as temperature changes. This resistance is translated into voltages in reference to the 5v reference voltage. This varying voltage indicates to the ECM what to do concerning ignition timing and fuel control. The ECT temperature sensor is used by the ECM for cranking air/fuel ratio and warm-up curves, climate control systems, and cold engine fast idle.
P0117 & P0118 Symptoms
No start due to flooded engine
Overheating (electric fan only), radiator ok
No fast idle when cold and when the engine is Hot idle still remain high, sometimes engine starts and stall.
Failed emissions or Black smoke
No air condition clutch engagement
P0117 & P0118 Causes are
Faulty wiring and connectors
Stuck open thermostat
Sensor defective
Temperature sensor ground shorting or missing
P0117 & P0118 - DYI Steps to fix it
STEP 1: CHECK THE ENTIRE TEMPERATURE SENSOR CIRCUIT
The temperature sensor has either two or three wires: temperature gauge, grounds, and signal. If it's two wires the ground is the sensor body. A Temperature sensor can be tested in two ways: by measuring either varying voltage or resistance. Voltage measurement is always the ideal test method because it gives accurate results and most ECM, and PCM reads these voltages. To check for the presence of a temperature signal, turn the ignition key to the ON position and leave the Temperature sensor plugged in. Back probe signal wire with a digital multimeter. The following readings should be found on each of the three wires:
STEP 2: A ground (0v or 0.02v) on one of the 3 wires indicates grounding coming from the ECM/PCM. If it's higher than 0.02volts there is the possibility that the circuit has high resistance or bad ground. Perform a voltage drop test on the ECM/PCM ground wire.
STEP 3: The second wire - a signal wire must not be either 5volts or 0v. It must vary from 0.1 & 1.5 volts if the sensor is Hot to 2.5 & 4.5 volts if the sensor is Cold. This is due to the variable resistor inside the sensor that changes resistance in relationship to the engine coolant temperature. Connect a multimeter positive lead to the signal wire with KOEO back probing sensor connector and negative lead of the multimeter to a known good ground to check the above-indicated voltages;
If readings show fixed 5v ( check sensor ground or open connector or thermistor). Confirm with a scan tool by jumping the signal and the ground wire, the voltage must drop to 0volts, and the temperature reading must be 260-400 degrees F.
If readings show fixed 0 volts, unplug the sensor, the reading must be 5v - which means the signal wire integrity circuit is good. If it remains 0 volts the sensor is shorting to ground or open in the signal wire. To know better use a scan tool - 0v means shorting to ground and 5volts means open signal wire.
If you’re not getting any signal at all or it's out of range, unplug the sensor, the reading must be 5v, which means the signal wire integrity circuit is good. You can also compare the ECT with the IAT sensor temperatures, the difference must only be 5 degrees. If the IAT is mounted on the manifold the reading is cooler than the ECT, if not but hotter than the ECT, the EGR solenoid valve is stuck open.
STEP 4: The third wire is for the temperature gauge on the instrument gauge on the instrument panel. If your instrument panel does not reflect temperature changes, check this wire for opens or high resistance.
STEP 5: A code scanner will display P0117 (low voltage - sensor or signal wire shorting to ground or open) or P0118 (high voltage sensor or wiring shorting to voltage, or open ground). With the scan tool connected disconnect the sensor connector and monitor changes in the temperature sensor PID, it must indicate -40 degrees F. With the sensor disconnected bridge or jumping the signal wire with the ground, it should read 200 - 400 degrees F.
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