Temp gauge normal operation
 

I have seen conflicting info on threads so I figured I would ask straightout

1999 SL1 On highway my temp gauge sits just above 1/4 tick (replaced thermostat in January when I was having a heating issue). Should this be closer to 1/2 tick(do I have a bad temp sensor)

I also have an issue with overheating in traffic. I figure the fan is not turning on (could that be same issue). Plan to check fuse on fan tonight.

One more question, what triggers the fan when the A/C is on. My A/C isn't blowing cold (Figure it needs a recharge). If that is the case will the compressor not turn on and therefore neither with the fan. I don't want to troubleshoot the fan incorrectly because something else is wrong and it shouldn't turn on.

Engine cooling fan turns on at or near the 3/4 mark on the temp gauge with a/c off. ETCS triggers the fan to come on. If you need to replace the etcs you will also need to replace the connector. Buy both from the DEALER.

+ 1 ECTS + Connector from dealer.
prob most common failure on S cars.

Fan will not tun on if failed ECTS tells PCM that coolant is always -40C.

A/C on does override and commands fan on.
__________
Start with ECTS (Simple)

We'll get more complicated if we have to

someone please call me on this ...

A technical service bulletin published February 2001, # O1 T 07 for S series Saturn cars refers to a new design engine cooling sensor. Part number 21025106. This is a 5 page service bulleting, much of it involved with the proper replacement procedure.
Notice the date of February 2001. Some 10 years or so after the first of the S series Saturns. So plenty of time has taken place to ensure that the aftermarket is well saturated with parts that match the original design of out of specification sensors.
The Engine Coolant Sensor is referred to as part number 12117087
The Coolant Temperature sensor is referred to as part number 21025106.
It is suggested that the connector be replaced IF it has the indication of corrosion or evidence of coolant in the connector.
The symptom appears to be a heat gauge indications of excessive heat.
And
Some indication of actual overheating due to improper operation of the engine cooling fan caused by the Coolant Temperature sensor. This being on the engines with two sensors, one for each function.
My personal experience is this;
Driven in excessive heat conditions where ambient temperature can be over 90 degrees regularly, the heat gauge will indicate that the engine is running hot due to false readings.
Under most circumstances this is not readily apparent as to a problem as heat gauges are inherently vague as to what they should read. My car when new regularly showed it to be running in the upper 1/3 of the gauge. It only surfaced as a problem when the catalytic converter plugged which actually caused an overheating problem or at least a problem of apparent overheating as indicated by the gauge.
Resolving the catalytic converter problem
and
replacing the sensors moved the gauge reading to the 1st quarter mark on the gauge.
An abbreviated resistance reading chart of the sensor reading is;
177 ohms read at 212 degrees F
2796 ohms read at 77 degrees F
9420 ohms read at 32 degrees F
It would appear to be difficult to purchase these parts from a Saturn dealer as the company is defunct and the dealers are probably out of business or now selling other cars. The dealer close to me is now a Volkswagen dealer.
Aftermarket for most people is probably the only alternative for parts. And due to passage of time, probably good ones.

Looks like UnclJohn has done his homework on this issue --> feel free to add a gold star to your chart.

The temperature vs. resistance listing is an important diagnostic and should be posted in your shop manual for future reference.

As far as parts go, I'm much more lucky, as the local Cadillac dealer in Mobile absorbed the Saturn crew, and still run a separate section of the shop floor

Saturn is closing oct 31st 2010, any and all parts will by that time shifted to other GM dealers. So again ..... BUY the parts from the DEALER.