1G 1g coolant temperature sensor

[90-GST]

so i searched around and couldnt find it on the site, probably because its a dumb question. but i have a 90 tsi awd that is throwing a code 21-coolant temperature sensor. the car is extremely hard to start when the car is cold, and most of the time i have to use starting fluid to get it to start. i have to hold the gas until it starts to warm up, and then it will idle extremely rough, but i know that is because of a vacuum leak.

anyways, i was wondering how to change the coolant temperature sensor. im pretty clueless and i dont even know where it is at to start with. if anyone could help me out that would be great.

 

[92AWDHX40]

That would cause a no start, look on the coolant thermostat neck, next to the head there are three sensors the gauge for coolant temp, fans and the coolant switch the coolant gauge has 1 wire the other two have 2 wires go to autozone or a parts store and tell them what you need.

 

[GRAVEDIGGER]

You need to find the thermostat housing where the cap is for the cooling system. The coolant sensor is right below that, near the top of the thermostat housing. It will have an electrical connector going to it. Below that is another sensor which has vacuum lines going to it (if they are still hooked up) and below that is yet another sensor, but the one you want is at the top (it sends info to the ecu).

 

[tunethis]

so i searched around and couldnt find it on the site, probably because its a dumb question. but i have a 90 tsi awd that is throwing a code 21-coolant temperature sensor. the car is extremely hard to start when the car is cold, and most of the time i have to use starting fluid to get it to start. i have to hold the gas until it starts to warm up, and then it will idle extremely rough, but i know that is because of a vacuum leak.

anyways, i was wondering how to change the coolant temperature sensor. im pretty clueless and i dont even know where it is at to start with. if anyone could help me out that would be great.

The sensor is the one with 2 prongs. When you find it, make sure it is still hooked up. My connector came loose and cause a CEL. The car started fine when it was hot but, once it got cold, it wouldn't start at all. The next day, I found the connector just hanging there.

A picture of the location can be found here.
http://www.dsmtuners.com/forums/problem-diagnosis/283796-coolant-temp-sensor-problem.html

 

[brownfinger]

The one you want has two wires. The terminals are perpendicular to each other; a sideways "T".
You unscrew it, and screw in a new one. Use teflon tape or sealant, unless the new one has some on it already. Coolant will gush out all over the place, by the way. You can drain the system, work really fast, or clean up a huge mess.
I like "work real fast".It goes like this: Wedge a towel under the sensor somewhere .Unscrew the sensor most of the way. Stand ready and steady with the new sensor in your right hand, while unscrewing the old one the rest of the way. Instantly slide in the new one, snug it in, wipe up the coolant that got away.
While the harness is unplugged you need to look really close at the wires for cracked insulation or broken wires. The CEL means that there is something wrong with the circuit, not just the sensor. It could be the sensor, or it could be a broken wire, or the sensor connector could be corroded.
Tell that bi*** who's boss!

 

[Mr Peepers]

I've seen the wires break off near the connector many many times, check that first.

The one you are looking for has two 1/4" spade style connectors on it, in this shape l- perpendicular to each other. There is another sensor for the a/c with 2 smaller pins in the connector, not to be confused.

If the wires are broken off, just crimp some 1/4" female spade connectors on the wires and hook it back up without the old plug.

As for the rest of the sensors, the one with the vacuum hoses is a thermoswitch for the EGR and the single prong is for the coolant temp gauge.

Looks like brownfinger beat me to a couple things

 

[brownfinger]

MrPeepers, I think we were racing.

 

[dsmfa9nutter]

That would cause a no start

After cranking forever, a car with a bad CTS would start.

 

[Hubbell91Tsi]

Can anyone tell me where the wires from the coolant temp sensor head off to? Back to the ecu or what? I have a 91 awd

 

[ilco187]

Can anyone tell me where the wires from the coolant temp sensor head off to? Back to the ecu or what? I have a 91 awd

yes they go to the ecu thats how the ecu tells how cold the engine is or hot it is, if the sensor is bad you will get a CEL reading and run like crap or have hard cold starts.

 

[dsmfa9nutter]

They go back into the loom that connects with the rest of the tb/cas sensor wires that combine with the fuel injector harness which snakes it's way back inside the cabin to the ecu.

 

[V8KLR]

I had my CTS go bad yesterday and all I did was take the 2 wires and grounded them on the thermostat housing. Car runs fine now

 

[bobglaub]

I had my CTS go bad yesterday and all I did was take the 2 wires and grounded them on the thermostat housing. Car runs fine now

Has anybody else done this? Mine CTS is bad and I did the same thing and she started right up. still have a couple issues to work out, but it started right up. Is there any detrimental damage that could take place by not having a CTS?

I am very curious to this fix. BTW, I plan on replacing my CTS soon, i'm just not in any hurry, she's not my daily driver, more of a project car. Also, if I did this, and tuned the car, would I have to re-tune it after I replaced the sensor?

 

[400HP1GT]

Can the A/C temp sensor be eliminated ? I have removed the a/c from my car. The ECM temp sensor is still hooked up, the A/C sensor is broken.

 

[jeffo]

Yes, if you are referring to the A/C thermoswitch at the thermostat housing. It is only used to shut the A/C compressor off if the temperature gets too high, so if you have eliminated the A/C you don't need it.

 

[9!'clipseDOHC]

Can anyone post a pic of this A/C theromoswitch? My A/C has been removed for several years. How do you remove the sensor/switch?

 

[SBR Joe]

Can anyone post a pic of this A/C theromoswitch? My A/C has been removed for several years. How do you remove the sensor/switch?

Its the only sensor on the water neck.

 

[9!'clipseDOHC]

Ok I figured it out... I think. First of all, the water neck it the upper portion of the Thermostat Housing. I made up this picture, but can someone confirm this info for me?

 

[Clutch GSX]

unscrew the coolant temp switch, buy a new one at the dealer (~$40) and screw the new one in using high temp thread sealant and your problem should be fixed. If not, check the wiring (or maybe check it before you spend $40...)

 

[9!'clipseDOHC]

Yes, unscrew the coolant temp switch, buy a new one at the dealer (~$40) and screw the new one in using high temp thread sealant and your problem should be fixed. If not, check the wiring (or maybe check it before you spend $40...)

I'm not looking to replace it, just to block it off. I'm going to try to find the bolt size today but I may have trouble since its Christmas Eve. I know that it is the exact same size as the vacuum control for the EGR which is also on the thermostat housing. I'm going to block off both just to clean things up a little. My A/C and EGR have been gone for years. Once I get the bolt/thread size I'll post it incase anyone else want to do the same thing.

As far as the picture, it has been confirmed several times on another thread. You guys can verify it here: What sensor is this & where can I buy it at? starting at post #9.

Ok I blocked them both off! The thread size is 3/8 pipe thread. I ended up using plugs instead of bolts. This is what it now looks like:

 

[Clutch GSX]

This is probably irrelivant but if anyone wanted to know, the plug from the dealer to block off those two ports is part number MS661162 and yes, it is 3/8. Although its probably cheaper to just buy a plug at a hardware store... Also, I would recommend using permatex thread sealant when installing those plugs, not too much though.

 

[9!'clipseDOHC]

Good find Clutch! Yes my way was much cheaper, free! Not sure how much it usually costs but when I asked the guy how much he just said to take it