first, my coolant temperature sensor is erratic.. sometimes it'll work just fine, sometimes it'll just sit at cold no mater what kind of driving i'm doing.

second is the outside temperature sensor which has been dangling and moving around inside the bumper since i bought the car. depending on its mood it'll read fairly accurately or just make up numbers

my question is, as the title asks, what are some of the effects of these dodgy sensors? reduced performance? overcompensation? or even more grim effects that i'm not aware of? there is no CEL present

either way i'll be fixing both but id like to be informed.

 

The only potential bad effect of the ambient air temp sensor is, if it reads below a certain temp, it'll turn on your mirror defoggers (if your car has them). Too much time with them on burns the fluid inside and turns your mirror glass brown. As for the CTS, it can give you difficulty starting, poor fuel mileage, rough running, and other similar issues.

 

man.. you sure know a shitload about these B5's.. thank you

my drivers side mirror is actually brown around the edges - as i bought it. i just figured it was some cheap replacement where the reflective material was coming off. makes a lot of sense considering that the ambient air sensor has been sitting and jumping around at the bottom of the radiator for who knows how long.

a lot of smaller issues are also explained with the bad CTS. on occasion itll have trouble starting, the mileage isn't all that bad but i spend more time working on it than driving it, and the idle is still rough despite my efforts replacing the vacuum system, spark plugs, seafoam, intake cleaning, MAF cleaned and/or unplugged, +

we'll see how the replacement CTS changes things if at all

 

You can just ziptie the ambient temp sensor up out of the way and you'll have way less damage and much more consistent readings, if it wasn't already broken. As for the CTS, a lot of your issues have been shared by other car's and have been solved with a new CTS in the past.

 

im glad i stumbled in this thread...my coolant temp has been doing the same thing. At first I thought it could be the thermostat, but im starting to lean more to the ECT...

 

Still need to change mine as well.

 

Yeah, don't go cheap on that one. Figured I might save a couple bucks and buy a cheaper no name at Autozone, but the POS only worked reliably for a week or two before crapping out. One more thing on my list!

 

which CTS is it? green, blue or black? i'm out of the country now and would like to have it shipped before i get back

 

Depends on your car - best breakdown I can give you is that in general the early 12v cars had the black sensor, the 30v and 1.8T dbc cars (98-99) used blue, and the later dbw (post facelift) are green. I'm sure there's overlap though but if you order from ECS, PureMS, or GermanAutoParts, you should be able to have them look up the right one based on your VIN number.

 

I have only just noticed a similar problem with my Temperature gauge. I have a 2001 1.8 quattro, Where does this coolant temperature sensor reside?