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Hello guys, just got a 95 Saturn,4 door,4 cyl, cant tell what model it is. The cooling fan wont come on by it self,but if i turn on the A/C, the fan comes on. If i then shut the A/C, the fan will remain on until the temp drops, but will not come back on by it self. What brings the fan on? I cant find a temp sensor. Thanks for any help.

You have (2)two temperature sensors, one for the dash gauge and the other one for the ECM/PCM electronics. The dash gauge is a single pin while the engine coolant temperature sensor is a two-wire one. The ects is located under the EGR valve to the right. It tells the ECM/PCM the engine temperature and the ECM/PCM develops the air/fuel ratio and when to turn on the fan. Replace it immediately with the replacement brass one and check the two-wire connector for any corrosion, replace it also either from the dealer ($30) or from a junk yard air intake temp sensor wiring harness.

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Thanks Ducky!

Hello


I have 2 questions relating tooverheating. 1 - where is the location of the sensor thathas athe single wire. I replaced the double wired one but I can't seem to find the single wired one. 2 - my Service light (not Check engine light) came on but is off when theA/C is on. This began when the double wired sensor was replaced.


Thank you in advance.


Maria

Hi Maria, I can't be sure but there was a cutoff, somewhere around '97 that both coolant sensors were combined into one, two-wire coolant sensor for the ECM and for temperature monitoring on the instrument panel. Your car my have the one sensor (it would help to post the year, make, model, mileage, etc.. Both sensors on the earlier cars are located one above the other so if you only found one I wouldn't worry about the second one. The two-wire one is the important one for the engine to know whether its cold, warm, or hot to be able to turn on the radiator cooling fan at the right temperature. The coolant sensor itself doesn't turn on the fan but tells the ECM the temperature of the engine and the ECM determines when to run the fan.


Your service light (also depending on the year of the car) means that there's a diagnostic trouble code (DTC) that is either pre '96 OBD I or post '96 OBD II (on board diagnostics) stored in memory. OBD I only requires a paper clip inserted into the OBD I port by the driver's knee area to make available a sequence of flashing lights that you count to decode the troubles. OBD II requires either a free scanner/reader that plugs into the same port connector by the driver's knee area and retrieves codes onto the reader's display for anyone to troubleshoot. The free scan may be from any large auto retailer or from buying a personal scanner. They range from about $50 to well over thousands of dollars as used by the dealers. Try http://saturnfans.comand their library of information to find out about codes, reading them, interpreting them, access to them from the paperclip method or from the portable scanner/readers. You must determine what year your car is and then use the appropriate OBD codes for determining the faults. Good luck. Find the code(s) then post them here for more assistance or on the saturnfans site.

Thanks Ducky for your comments.


I have a 99 SL2. I understand about the sensors now. My service light (wrench)still has me stumped. It coming on when I start the engine. I took my car to Auto Zone and there were no codes to be read. The gauge read "passed". However I recently notice my car does not overheat when I have the A/C off - at this time the service light is on. When I turn the A/C on - the service light turns off and if I am sitting at a long light the car tents to get warm fast. It will eventurally move near but not into the red zone. I do not see the fan kick in unless the A/C is on. Could the service light be tied into the A/C somehow. Plus the engine will idle high (2000) whenit starts to around the 1/2 mark on the temp gauge.


Again thanks.

Ok, '99's are OBD II and there should have been a code stored and displayed when A-Z plugged in their scanner. You still may have a coolant sensor problem but with the wiring connectorinstead. First, the coolant sensor should be the brass replacement one and second, the two-wire connector should be inspected closely for any signs of corrosion (green slime) preventing good electrical connections. Replace the connector either from a junk yard intake air temperature connector or the dealer's $30 part. I believe the fan won't come on until nearing the red area on the temperture gauge. The high idling may be from a sticking throttle body/linkage requiring cleaning with carburetor cleaner or from a sluggish/sticking idle air control valve (IACV). The iacv is attached to the throttle body and should be cleaned with electronic contact cleaner. Its a precision servo motor with afeedback circuit to the ECM that adjusts the idle speed through a bypass air portfor normal, a/c operation, closed throttle deceleration for emissions control, and for cold starting raising the idle speed for a quick warm-up and gradually lowering the rpm until the engine warms up.