Engine coolant temperature sensor

[one1ove]

My ECT gauge has been acting up, going from 0 to half and then back randomly at all times. MY CEL came on at one point but went off again. Is this the ECT sensor? Do I need a new part? if so, what part #? thanks

[Poopie]

yes, the question has been answered before. you can find the part on ecs or just go to the dealership. it should onle be $20-$30.

[t1demont1]

if you go to a vdub or audi dealership and tell them you need a coolant temp sensor for whatever year your car is, theyll hoook you up.

[flyromeo3]

i dont think the the coolant sensor will throw a CEL ?
Can someone correct me on this .

[SykoraA4]

it will, i had one, and i thought it was causing my boosting problems. i replaced it. so now it doesnt throw that code anymore... but i still dont boost right...

[Nebone]

It does throw a CEL. It can sometimes be a tricky bastard and throw a CEL thats not related to it but caused by it. You need to search your code and the cause will most likely be that sensor.

What year and engine in your car?

[flyromeo3]

i think he has a 01 a4 1.8

[Nebone]

It totally sucks to replace that sensor on the 01. You have to literally hug the motor with both hands. You'll know what I mean when you get to it.

[4bagels]

That sensor is actually 2 sensors in one (bonus!) That's why there are 4 conductors, half go straight to the gauge, the other half go to the ECU.

So if the gauge side of the sensor goes bad, then your gauge starts acting flaky but it doesn't throw a CEL. Or if the ECU side of the sensor goes bad, you can get a CEL but your gauge runs fine. Kooky.

[jpo]

I threw a CEL for the ECT sensor..what is more I was having boost issues (i.e. slowest car on earth for about 10 mins after start up) that went away after the sensor was replaced.

[JoBuNY]

I got a CEL from my ECT and it was covered under that extended warranty thing from Audi they mailed out. I got my letter back in like April or May of this year. I have a 2001 A4 so you should be covered on yours as well.

[Nebone]

^ O yea. Just go to the dealer and they will do it free of charge.

[E Blacklock]

Was wondering if your ECT gauge would never "warm up" on drives, or if the gauge was actually broken.
What's happening with mine is I would go for a long drive and the gauge would never say it's warmed up. I would stop for something to eat, turn the car back on and the gauge would say it's warmed up. Then after driving a while it would cool back down.
Was wondering if that's the gauge or something more expensive?
Thanks

[4bagels]

that could be your thermostat - common failure mode in our cars.

[walky_talky20]

Yes, could be thermostat, or could be the sensor. My car was doing the same thing a while back (reading cold while driving, and fluctuating). Changed the thermostat and it was all good. 3 months later it started doing it again! I was like, "another thermostat, really?", then one day the car was really hard to start and threw a code for the ECT sensor. Changed it and the gauge reads normal now.

If you have vag-com you can compare the ECU's temp reading to your gauge. If they don't agree (gauge says cold, but ECU says ~90c), then the sensor is bad. If they do agree, then the car is *actually* running cold and it's probably your thermostat.

[E Blacklock]

Thanks! The computer and the car agreed on temp, so that gave me the answer.

[d3br34k5]

It does throw a CEL. It can sometimes be a tricky bastard and throw a CEL thats not related to it but caused by it. You need to search your code and the cause will most likely be that sensor.

What year and engine in your car?

Just to add some credibility to this statement, I picked up a Bank 1 too lean code earlier this week. I had no idea what was going on until I was driving the next night and the coolant temperature on my cluster fell to 60 (ECT sensor stopped working). I guess it was on its way out and wasn't sending the proper temperature to either my cluster or the ECU.

I ran VCDS the last couple of days to make sure my coolant was at the right temperature and logged my trim levels. Coolant (group 2) was reading fine at 90-95C and my trim levels (group 32) were 8.3(add)/-3.0(mult). Swapped the sensor today, cluster is working fine again and my additive trim has started to normalize.

I didn't clear the MIL yet, waiting to see if it will go out on its own as my trim(a) levels get closer to 0.

There was no DTC specifying the ECT sensor was going bad, just the lean code. On a related note, what a pain that thing is to get to. Be careful not to upset the braided vacuum line on the Kombi-valve if you haven't already swapped that line out.

[jahnetik]

Would a failure of the ECT cause the temp gauge to not work AT ALL and a slow depletion of the coolant from the coolant reservoir?

[QuattroGinger]

if its the thermostat i would think it would overheat because of it not opening.

[Seerlah]

If the thermostat was stuck closed, the car would overheat. If it were stuck open, it would take longer for the oil temp to warm up (probably would not warm up till driven). The CTS on the rear coolant flange would make your gauge be off. Bad thermo can also do the same thing.

[walky_talky20]

Would a failure of the ECT cause the temp gauge to not work AT ALL and a slow depletion of the coolant from the coolant reservoir?

Well, the gauge needle is always pointing to *something*, so it is always "working" (ie: pointing to a temperature). Whether that temperature is *accurate* is the question. If the thermostat is stuck open (or removed), it would be expected that the coolant temp gauge would hardly move under average driving in cold weather. The other possibility is a faulty coolant temp sensor, or a faulty gauge. The gauge can be tested directly using vag-com's "output test mode" on the instrument cluster. It can command each of the gauge needles to move throughout their range. If the gauge itself is broken, that test would show it. Vag-com could also look at the incoming coolant temp value to the cluster. You could compare that to the incoming coolant temp value to the ECU (or to the physically measured temperature of the engine coolant using a thermometer).

As for the leak, that would be a completely separate failure from the electronics, obviously. It could be the coolant temp sensor's o-ring that is leaking, or it could be the plastic coolant flange that it is mounted in. Both are common leaks. Other possibilities are hose connections, leaky radiator end tanks, etc. Generally cooling system leaks are found by the evidence of the leak (crusty pink stuff in the case of OEM Audi coolant) or by doing a pressure test of the cooling system and watching for the leaks in real time.

if its the thermostat i would think it would overheat because of it not opening.

The most common failure mode of a thermostat is for it to stick OPEN, making the car run cold. They are designed to fail in this manner, it is a fail-safe.

[FU5E]

Im having the same problem, my collant flange is leaking and I asked the dealer for the flange and the sensor, I got the flange? I have a 2001 1.8t do I need to call them with a part number or is this it? this thing is burried deep back there I only want to get back there once.

[Seerlah]

You need a replacement o-ring also for the flange. The coolant flange are block specific (or cylinder head specific) so it must be for the AWM. Part number is 058121132C. It will be molded onto the flange, so you just need to confirm you have the correct one. And you can pick up the sensor for $15 shipped from MJM (CTS also needs new o-ring).

http://www.mjmautohaus.com/catalog/p...oducts_id=1207 (comes with o-ring for sensor)

And to throw in a curve ball, my rear coolant flange was leaking. I inspected it, and found the flange to be just fine. So, I just replaced the o-ring (sourced the leak to here) and everything was fine after that. I would suggest you watch where the leak is actually coming from on that flange. But since you already have a replacement flange, might as well just swap it in. Only issue is it is more work in a really tight space.

[walky_talky20]

For a 2001, you want to have the following on hand if you are going back there:

Flange:http://www.ecstuning.com/Audi-B5_A4-...ges/ES2187573/
Sensor:http://www.ecstuning.com/ES2535414/
O-ring for sensor:http://www.ecstuning.com/Search/N90316802/ES2467/
Clip for sensor:http://www.ecstuning.com/Search/032121142/ES1906430/
O-ring for hard pipe:http://www.ecstuning.com/Search/058121687/ES250825/

I asked the dealer for the flange and the sensor, I got the flange?

Sounds like your dealer sucks...just sayin'

[FU5E]

Yup they dropped the ball on me

Did get the leaking flange fixed though would have been nice if send me all of it, included all of it. So now I just have too wait for a sensor

Thanks for the info though it helped me out

[bmarshall]

I have a leaking flange snd found there was a bit of degredation of the plastic where the o ring sits.

[QuattroGinger]

fuck those flanges. my timing belt kit was easier for me to do than that thing. lol