Replacing engine coolant temperature sensor (ECTS) – 1998 Saturn SL2

ECTS and gaugeI recently purchased a used 1998 Saturn SL2, and one of the first things I noticed was that once the car had warmed up, the dashboard temperature gauge was always pointing slightly less than the 1/4 mark and never went any higher. I thought this was a bit odd, since all my previous vehicles would usually stay just below the 1/2 mark, but then I figured that maybe the SL2 engine just stays cooler. Not so. Doing a quick search online uncovers the fact that one of the most common problems with the SL2 is a cracked coolant temperature sensor and/or a stuck-open engine thermostat. Either one of those will cause the dash gauge to stay at the 1/4 mark pretty much all the time after warming up. A correctly-functioning SL2 should stay about halfway between 1/4 and 1/2 (i.e., at 3/8). Replacing the thermostat and the engine coolant temperature sensor (ECTS) are some of the easiest repairs that you can do on the SL2.

This post describes how to replace the engine coolant temperature sensor (ECTS). If you want instructions on how to replace the engine thermostat, then view my other post here: I recommend replacing both the thermostat and the ECTS at the same time, because they are easy and relatively inexpensive. Furthermore, replacing either part requires draining the coolant from the engine and radiator – so you may as well replace both since the coolant is going to be drained. The ECTS was about $5 and the thermostat was about $15 from, or $12 and $17 respectively from

Materials Needed

  • 13mm deep socket
    (for the ECTS, I have the Tekton 1230 deep socket set)
  • 10mm socket (for everything else)
  • socket wrench
  • fluid drain pan
    (must hold 2 gallons of coolant, here’s mine: Hopkins 11845)
  • coolant/antifreeze (up to 2 gallons)
  • ECTS, brass tipped (Tru-Tech TX73T)
  • thermostat, if you are planning to change this at the same time (Stant 14279)
  • pliers

First of all, the Saturn coolant temperature sensors are notorious for going bad because they are made out of a material that cracks, allowing coolant inside the sensor and causing it to malfunction. When you purchase a new ECTS, make sure that it is the brass-tipped version so that it will not crack again. See the picture below to see the difference between the cracked ceramic ECTS and the updated brass-tipped ECTS. Let me repeat – both are still sold in stores, so make sure you are getting the brass-tipped version. I used part number TX73T (the manufacturer is Standard Motor Products), purchased from RockAuto.

ECTS - ceramic vs brass
Old, cracked ceramic ECTS and the new, stronger brass ECTS. Note that the blue on the new ECTS threads is the Loctite that I added, it did not come with that already on. Click image to enlarge.

Location of Engine Components

Refer to the three pictures below to see where the engine thermostat, engine coolant temperature sensor (ECTS), coolant reservoir, engine block coolant drain plug and radiator drain plug are all located.

Component locations
The locations for all of the components referenced in this guide. Note that only the general vicinity of the engine block and radiator drain plugs are shown in this image – their specific locations are further depicted in the next two pictures below. Click image to enlarge.

Thermostat and drain plugRadiator drain plug
The locations of the thermostat and the coolant drain plugs on the engine block and the radiator. All three are right behind the radiator, directly below the air conditioning compressor. Click images to enlarge.

Replacing the Engine Coolant Temperature Sensor (ECTS)

  1. Let the car cool down. The car has cooled sufficiently if the metal of the engine block is cool to the touch. The last you want is scalding hot coolant pouring on you when you replace these parts.
  2. Open the hood. Become familiar with where the engine thermostat, engine coolant temperature sensor (ECTS), coolant reservoir, engine block coolant drain plug and radiator drain plug are all located. See the previous section ("Location of Engine Components") for pictures of these locations.
  3. resevoir cap offRemove the coolant reservoir’s cap. This will allow the coolant to fully drain from the system when you remove the drain plugs.
  4. Engine drain plugDrain the engine block coolant into the drain pan. The first drain plug is on the engine block, directly below the thermostat (see picture). It is accessible from underneath the vehicle using a 10 mm socket. Back out the bolt most of the way with the socket wrench, and then unscrew it the last few threads by hand so that you can avoid getting engine coolant all over your tools.
  5. Radiator drain plugDrain the radiator coolant into the drain pan. If you are only changing the ECTS and not the thermostat, then you can skip this step. If you are replacing both the ECTS and thermostat, then note that the engine block drain plug in the previous step and the radiator drain plug are very close to each other, so if your drain pan has a large opening then you can remove both plugs and have the pan catch both streams of coolant as they drain. Most radiator drain plugs I have seen have a tab on them and are removable by hand without any tools. However, my radiator drain plug had a very unusual 1/4-inch ratchet-type connector on it and I could not remove it. If this is the case for you, too, then you really don’t need to drain the radiator from this plug, just continue on with the steps below.
  6. Air intakeAir intake removedRemove the air intake duct assembly. This is very simple for the SL2, since it only requires unsnapping the 4 air filter brackets (by hand), pulling off the small hose going to the DOHC valve cover (by hand) and using pliers to release and remove the ducting at the throttle body (see picture for locations). The throttle body is where the duct connects to the engine – use some pliers to squeeze the circular metal fastener’s tabs together while simultaneously pulling the duct away from the engine. Also remove the air filter.
  7. location of ECTSFind the ECTS. It is located about 9 inches beneath where the spark plug wire are connected to the DOHC valve cover. See picture.
  8. Removing the ECTS connectorOld ECTS with connector removedRemove the connector from the ECTS. It does NOT simply pull off. You need to use pliers to grab the two shorter edges of the connector (see picture), and then squeeze the sides together while gently pulling the connector with the pliers. It should take very little force to pull it off. If that doesn’t work well, then try getting your finger back behind the longer edges of the connector and lightly pry one and then the other over the small molded ridge that is there on the end of the ECTS. You should only pull on the connector casing, never on the wires. The pictures to the right show removing the connector with pliers, and the ECTS with the connector removed.
  9. Removing the ECTSRemove the ECTS with a 13 mm deep socket. You need to use a deep socket to do this because a standard socket will not fit over the ECTS body and a standard wrench will not fit into the small space where the ECTS is located. I also had to use a 1.5-inch socket extension to be able to comfortably access the ECTS for removal.
  10. Inspecting the ECTSInspect the old ECTS. Look for a crack in it, like mine had (see picture at right). You might also notice some green sludge in the 2-pin connector mating area from the coolant seeping through the cracked sensor.
  11. New ECTS with LoctiteAdd Loctite or Teflon tape to the new ECTS (unless the ECTS you purchased comes with it already applied). You are supposed to use blue Loctite (or equivalent), but I’ve read online that many people use plumber’s Teflon tape instead with good results. However, note that some temperature sensors rely on an electrical connection through the threads, in which case Teflon tape should be avoided (thanks for the tip, Jim Z). I used Loctite 6-ml Threadlocker 242. Note that when using Loctite, you only need to put a small amount on – barely enough to cover a few threads (it will spread itself out when you screw it in). You are supposed to add this to the threads for two reasons: to help keep the threads from corroding and to secure the part once installed so that it does not come loose from the engine’s vibrations.
  12. Newly installed ECTSInstall the new ECTS. The 13 mm deep socket wrench is actually probably a bit TOO deep, so you should start installing it with just your fingers at first, and then switch over to your socket once it is part way in.
  13. ECTS with connector installedPlug the connector back in. Make sure that it clicks into place. It should stay in place even with a gentle tug. To get mine to click into place, I had to push the connector on, and then press the longer edges of the connector toward the body of the ECTS so that their small notches would click past the ECTS’s ridge.
  14. Install the air intake assembly. Make sure to put the air filter back in first, and then reconnect the duct to the throttle body, push the small hose back onto the valve cover, and clip the 4 air filter housing clips back into place.
  15. Are you also going to replace the thermostat? If you are, then now is the time to do that. Go read my other post that explains how to do that here:
  16. Wait 20 minutes if you used liquid Loctite on the ECTS threads. If you used Loctite, then it takes 20 minutes for it to partially cure before you can start the engine or fill your coolant reservoir back up. If you used Teflon tape, then no waiting is required.
  17. Filling the coolant reservoirRe-install the engine and radiator drain plugs and fill up coolant reservoir to the max cold line. Start your engine. Turn the heater on full-blast. Let the engine warm up to normal operating temperatures, and add more coolant if the level goes down. Note that you might want to help "burp" it to get excess air out of the system – do this by repeatedly squeezing the large coolant hoses that go to/from the radiator. When you do this you will probably notice some air bubbles coming up in the reservoir.
  18. Re-install the coolant reservoir cap. You don’t want to accidentally drive off without having this in place!
  19. Temperature gauge at normal levelTake the car for a test drive. Drive it around for several minutes – you should see the temperature gauge go up to about half way between the 1/4 and 1/2 marks. After you are done test driving the car, let the engine cool off again and then check the coolant level in the reservoir and add some coolant if needed to get it back to the max cold line.

Additional Considerations

Keep your eye on your dashboard warning lights for the next few days. If you have a coolant leak somewhere, then your reservoir will detect when the level gets dangerously low and will start blinking a coolant/radiator light on your dashboard. If that happens, then check if you need to fill your reservoir back up and check for leaks.

As previously mentioned, it is not necessary but highly recommended to replace your thermostat at the same time as replacing the ECTS. For instructions on replacing the thermostat, see my other blog post that describes that (

20 thoughts on “Replacing engine coolant temperature sensor (ECTS) – 1998 Saturn SL2”

  1. So glad, you posted this information, we had replaced my idle air
    control sensor, my pocket pc detected it had a problem, plus a mechanic
    told me during the summer it would have to be replaced soon. Then the next
    code that came up was a throdle position sensor, replaced that, still have problems with my rpms. Took your advice and checked and purchase a Engine coolat temp Sensor and it was ceramic and was cracked on 2 sides! AMEN I believe this was part of the major problem. Bought a new one, like you said with a brass tip, installed it and now my car seems to be idling a lot better. Still wants to stall out ocassionally, but maybe everything will reset in time. Thanks for much for your great post.

    Margaret Shields
    Tallahassee, Florida

    1. Margaret i know this was posted 4 yrs ago but i was curious as to if u still had issues with your saturn after you replaced the sensor? It sounds identical to the issues with mine. If you get the time could u please email me? Thank yoj so much!

  2. Thank you for the outstanding instructions. They were very easy to follow and right on target. My 1996 Saturn SL-1 would not pass emissions as only two out of the five sensors were showing ready. I followed the advise and suggested drive cycles of local mechanics to no avail … sensors were still not ready after about 300 miles of driving. I replaced the ETCS sensor per the instructions provided and flew through emissions with a “pass” just an hour later. Cost of the sensor and new coolant was about $42.00. Local mechanics get $85 per hour. The whole job took me about 50 minutes to complete. I can’t thank you enough for the information.
    Thank you again,

  3. Thanks again for such complete instructions. I am so grateful for people like you who take the time to write such detailed instructions. A few years ago, I had a problem with my SL1 where it idled poorly when it rained or the humidity was very high. Took it to a repair shop and they replaced a couple sensors and set me back about $400. Problem didn’t go away and in desperation, I Googled the symptoms and learned about corrosion under the ignition coils. Cost me $6.00 for a tube of Dielectric grease and some sandpaper. Problem is gone. I’ve resolved to do my own repairs as much as possible and to never take a car to a repair shop without having diagnosed the problem myself. The Internet and people like you have been so helpful.

  4. Great info thank you very much for that how-to article. One word of caution, however, when using teflon tape on temp sensors. Some sensors must ground electrically to the engine and using teflon tape may prevent that from happening, so you may want to go with the locktite.

  5. got a problem. tried replacing the sensor myself. i took out old one and put new one in. overtightened it, and it broke off flush right at the end of the threads (where the threads end and the part that connects to the wires begins) ive brought the car to a few mechanics, one told me he didnt want to do the job of fixing this, the other said id have to remove the cylinder head in order to beable to access the sensor, (from what i understand this would not give ACCESS to the broken sensor.) what do i do? is there anyway to remove this sensor and put a new one in thank you ryan.

    1. Yikes! The only thing I can think of to try (which some people use with broken bolts) is to use a dremel tool to cut philip’s head screwdriver marks into the remaining sensor body, then unscrew. However, I would have to suggest to do this at your own risk, since who knows what the internals of the sensor are made out of and you might end up causing more damage this way…

      You could also try using those backwards-threaded screw/bolt extractor drill bits that you can use to back out bolts that get broken off (like these: But once again, you run the risk of it not coming out, drilling through the sensor, and getting debris into your coolant lines.

  6. Thanks a lot for this info, is really awesome and helpful.

    I have a question, couple days ago a mechanic changed the ECTS and thermostat but he didn’t remove the air intake duct when he did the job, is there any problem with that ?

    Also, the gauge is moving about 1/2 when I’m driving, once stop the car, the gauge goes more than 1/2, if I drive again the gauge comes down just a little bit less than 1/2 and so on…. (never reach the 3/4 or get a light on) also I checked the coolant and was not boiling.

    Btw this is my first saturn and I don’t know if is normal or not.

    Thanks and sorry for my English.

    1. Cesar,

      Yeah, it’s fine that he didn’t remove the air intake duct. It is just much easier to do the job if you remove the duct.

      It is normal for the gauge to stay at around 1/2. If I’m driving in traffic it stays at that value. It should never go much higher than that, since at that point usually the electric radiator fan has kicked in and the thermostat is probably fully open. I wouldn’t worry too much about it unless it starts to regularly stay around 3/4 or a light comes on.

  7. Does the ECTS, which operates the temperature-display gauge , also control the “turn-on” critical-temperature for the Electric Radiator Fan (ERF) — when the air conditioner is not turned on? Or, is there anothe “sensor”?
    I am experiencing the same problem with the temperature gauge that you describe , and in addition the ERF does not turn on — I have had two recent “boil-over” episodes when I got into a stop-and-start traffic situation. I subsequently observed on these occasions that the ERF was not running. I am in the process of “gearing-up” to fix this problem, so I am collecting salient information related to this “malady”.
    Kudos, Mr. Thomson, on a truly top-class set of instructions.

    1. Yes, this would also be used for turning on the fan. If you are boiling over and the temperature gauge in your dash still reads a low temperature (1/4 mark), then you definitely have a faulty ECTS. After you replace your ECTS, you should still monitor your fan to make sure it turns on, too, just for ease of mind.

    2. Also note that if you’re boiling over, you should definitely also change the thermostat, as it might be contributing to the problem if it is stuck in a semi-closed position. Generally it is best to replace the thermostat anyway, since it is a cheap part and you’ll already have the coolant drained for the ECTS, too.

  8. When the engine coolant temperature sensor is defective, the vehicle may be hard to start ,get poor fuel economy & cause the vehicle to overheat.When replacing the engine coolant temperature sensor, always use a factory part, clean all the connections, and ensure that the entire cooling system is in good working order with fresh, clean coolant.

  9. I just recently replaced both of these parts and the temp gauge inside vehicle is still registering 1/4 but the car is still getting hot. it will run for about ten minutes then it just dies. what is causing this?

  10. I got a 99 saturn w2 was replacing connector pulled on black part where it clicks at the yellow wire came out of the pigtail connector is there anyway to out it back in? My car won’t stay running I think it’s because the sensor not getting full connection. If I do gotta get s new pigtail 2 wire connector where would I get one?

    1. It might be best to replace it if the current one is in bad shape. From what I’ve read before, most people go to a auto junk yard to get one of the connectors from another car (apparently a lot of the GM connectors are the same across cars). Otherwise, you’ll have to get a new crimped pin on the end of the wire and put it in. Not sure how available the individual components are.

  11. The connector was for temp sensor on block the black wire still in it but yellow one is out not

  12. You are a life saver! You have the most comprehensive and thorough process. I got the Haynes book and looked all over and nothing came close to your post here.
    Keep up the great work, you are a necessity to backyard mechanics everywhere

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