ETC CODE AND HAVE REPLACED COOLANT TEMP SENSOR

Are any DTC'S - diagnostic trouble code's stored in any module ? BCM - body control module , PCM - engine computer ,IPC etc.... It's the temp. gauge not thermostate gauge Did it work after replacing the thermostate an coolant temp sensor ?
Engine Coolant Temperature Gage
The instrument panel cluster (IPC) displays the engine coolant temperature as determined by the engine control module (ECM). The IPC receives a serial data message from the ECM indicating the engine coolant temperature. The engine coolant temperature gage defaults to 38°C (100°F) if:
• The ECM detects a malfunction in the engine coolant temperature sensor circuit.
• The IPC detects a loss of serial data communications from the BCM.

The first thing too do would be to hook up a factory or some other type of professional scan tool an see what the temp. sensor is telling the engine computer an if the BCM is showing the same temp. data . And is that info. getting to the instrument cluster . Knowledge of how it all works an proper diagnostic technique is the key to finding the problem .
If the IPC is see same temp the engine computer is an the gauge isn't working something is wrong with the gauge itself. New instrument cluster would be needed .

Why ? Temp gauge not working , cooling fans not working ? Is the check engine light lit an you have a coolant temp. sensor code ? The coolant temp. sensor is a input to the PCM/ECM - engine computer . If bad would turn on the check engine light. Trying to save you money an time replacing a sensor that may not need replacing .

This code means the fuel mix is too rich, and your O2 sensor is telling the ECU this is so. Look for other reason mix is rich, such as bad tune up parts, ignition module, coil, coolant temp sensor, etc.

code p0118 refers to engine coolant temperature (ETC) sensor ---circuit malfunction===causes---coolant thermostat---wiring open circuit/short to positive---wiring short to ground---ground wire defective---ECT sensor.. The temp gauge works off a temperature sender unit separate to the coolant sensor and if it is reading 100 then it indicates an overheat situation in the engine . Probably why the engine light is coming on. As the thermostat is in the list of causes I would replace it as a precaution. The coolant sensor is what tells the CPU to turn on the electric fans to cool the radiator

You would need a scanner and an inferred temp sensor to troubleshoot the system.
You need to know what the actual engine temp is, and what the temp sensor is telling the computer.
If and when the engine reaches 220 degrees, the engine temp sensor should be sending that data to the computer and it should ground the fan relay to activate it.
Unplugging the sensor and having the fan run tells you the sensor is connected, and there should have been a trouble code set at that time.
It is possible the coolant level is low, or something else preventing the temp sensor sending the correct data.

That code is for the coolant temp open circuit. More than likely replacing the coolant temp sensor will correc the issue but check/verify the connector and wiring for the temp sensor before you replace.

p0300 is usually a random cylinder miss-fire code, and i think that p0117 is coolant temperature sensor? Try replacing the sensor, could also be the reason for the other code, as a malfunctioning coolant temp sensor will affect engine timing.

2003 saturn vue, we dont have the engine size, the codes should be and are the same, po 128 means; cooling temp is out of spec, make sure the coolant is full, then replace the coolant emp sensor and make sure the connection is good, i would also replace the thermostant, this is a common code on these and most of the time its the coolant temp sensor or thermostant, ive learned to replace then both to avoid future engine lights with code po128. next we will check the code # po421, this code is that the computer sees that the cat converters are taking to long to warm up, code po 431 is also the same as po421, this code is related to the thermostant and sensor, the sensor give the computer the wrong temp readings and then the compuetr thinks the engine is hotter than it is and thinks the converters should be also hot like the motor but the coolant temp is giving a false reading, if you replace the coolant temp sensor and the thermostant and fill coolant , then reset the light and you will solve the problem, i hope this is helpful, also the sensor is located to the right of the engine if you are standing in front of the motor, heres a picture of the sensor, remember to check connector heres a pic of the connector, good luck.

PO183--Engine Fuel Temp Sensor,Verify PID Value
PO420---Catalyst System Efficiency Below Threshold (Bank1),O2 Sensors,Coolant Temp Sensor,Misfiring,etc
PO430--- Catalyst (Bank2)
PO462---Fuel Level Sensor Circuit Low Input,pump module,etc

Well----Codes do not tell you what part to replace,Just that a possible system failure has ocurred
Unless you have a scanner,not a code reader and a trouble chart,your done.
No experience,done

I would speculate, that you only have a couple of, not too serious issues,but wouldn't guess,it doesn't work that way.
Always test,and only replace things if they fail a test.

Is the battery okey and alternator output good ?

Sometimes there are two Temp sensors. Did you see if you had two?