Saturn S-series Starting Rough or Not Idling Well?

1991- 2000 Saturn S-series owners sometimes complain about rough starts or rough idling. In some cases it's a cause for the car not to start even though the starter is fine and the battery is at it's best. There is a simple reason for this that most owners don't know about.


So What's The Deal?

It's simply actually. It's called the Engine Coolant Temperature Sensor (ECTS for short). The what?! It's a basic thermoresistor (a resistor that changes it's resistance based on temperature) that is in a place where coolant flows past it. It tells the car's PCM (computer) how hot or cold the coolant is. Of course when you let your car sit overnight and come out in the morning to start it the coolant temperature is close to ambient temperature. When the car is started the coolant starts getting hotter and the ECTS tells the PCM the temperature as it's rising until eventually at full operating temperature.


Then What's The Problem?

Saturn used a plastic tipped sensor which is prone to cracking because of the constant heating and cooling cycles it sees. Coolant sees anywhere from -10 degrees Fahrenheit to 230 degrees Fahrenheit as does this sensor. So you can imagine plastic wasn't the best idea. It gets worse though. When this sensor cracks it allows coolant to flow to it's two wire connector and thus ruining the connector with old gunky coolant.


So This Has to Be Expensive and A Long Procedure To Fix...

Not at all! It's actually a very cheap sensor and in an easy place to replace. The nice part is that this was remedied in 2001 when Saturn switched to a brass sensor that does not have this problem. The part can be found at a local AutoZone or Advanced Auto or simply from you Saturn dealer (if one is still around). Ask for a Engine Coolant Temperature Sensor and when they come back check that it is brass (which is pretty obvious because the plastic tipped one has a very smooth rounded leading edge while the brass is more flat on the top).

The sensor is located just under and behind the upper radiator hose entrance into the head (might have to remove the intake tubing). It has a two wire sensor going to it. Check to make sure you're not changing the one that goes to the dash gauge on early S-series (91-95).

Remember to do this when the car is off and cold.

This should fix your rough starts and rough idling. If it doesn't, check the connector to make sure it isn't gunked up and put it all back together.