Coolant, temp gage problem HELP!
 

Next problem, something in the coolant system is messed up. While idling the temp gage stays all the way cold then in a few minutes will go half way, then the fans turn on and the gage will go all the way cold. I replaced the coolant temp sensor, didnt help. Still throwing a p0118 code. What could the problem be now?

That code says "input high", dosen't mean the sensor is bad at all. Whatever sends the 5 volt reference to the end device is probably at fault. Reading control voltages at that small of a degree, the ecm has to be more "exact" at what signal comes back. A .1 or .2 of a volt can mean 20 - 30 degree difference in actual temp (ex.)

What sends a 5 volt reference to it then?

I don't know, but would guess the power train control module. Programmable controllers such as the ecm (reads only, or read/writes) in "cars" send a 5 volt signal to end devices, then reads either in volts or miliamps the return signal that represents temp, speed, or whatever it is, for the ecm to determine (i.e.) cooling fan on, speed for cruise control ect. It took me awhile to realize what code I was reading on 5 volt reference signal hi on a crank position sensor code, then I realized what I was dealing with was a simple plc. These codes WILL tell you what is the issue, you just sometimes have to "anaylize" the wording.

Thanks. How do you suggest I go about fixing this problem?

If you have a Haynes or Chilton manual covering your car, trace the temp sensor wiring to whatever reads it, i.e. power train control module or whatever. I think I can look up what supplies power to it for you. ECM is exspensive probably 200 bucks for a remain, but son says for your car that is it.

ECM for '04 is around $65 on eBay with your VIN flashed in, is '98 that much more?
About your problem, if there is too little coolant in the system (air pockets) you may encounter same symptoms, just my 2c.

Yes, good advice. As stated you will need the vin for a remain ecm.

Is there anyway a broken thermostat could cause any of this?

no.


if you have 5volt key on at the yellow wire the brown return wire is probably open.