Slow and irratic ambient temperature reading (Climatronic)

[Juka]

2001 Octavia Combi 1.8T with Climatronic. Symptoms, after I start up the car the initial (correct) reading is stuck for at least 5-10 minutes, then it starts working but kind of irratic. I know this as I have an underground garage that throughout the year is 13~17°C, and immediately when I leave it the temp reading goes up or down, in a matter of maybe a minute I get the actual ambient temp, same thing when I return to the garage.

 

I had no problems whatsoever with ambient temperature readings until I changed both radiator fans (?!). I went back to the electro-specialist shop who did the change and told them about it, they changed the ambient temp sensor and it was still the same, after that they connected to diagnostic and saw that the ECU actually reads the correct temperature on all three sensors (ambient in the bumper, intake on the AC and inside temp) - but the one shown on the dash and climatronic is stuck. They disconnected the Climatronic and reconnected and it worked for a few weeks but now it's coming back.

 

Anyone has any ideas what it might be?

 

@Stjepan

[mac11irl]

a broken temp sensor in the climatronic would be my guess..

[Juka]

3 minutes ago, mac11irl said:

a broken temp sensor in the climatronic would be my guess..

Is it a common failure, where could I find the sensor, and is it DIYable? 

[mac11irl]

have no idea tbh, I dont have experience with climatronic...

but on the basis of your post, it seems a logical starting point?

 

[Juka]

Eh, but that's the thing, all three sensors are working fine, but the display temp is stuck... Wanted to find out if anbody else had these issues with climatronic. 

 

(me tbh, I wanted a car with classic AC but ended up with a loaded one, precisely because of such electronic gremlins) 

[mac11irl]

sorry, I think I mis read your description of what's reading what...

 

could be a corroded wire that disconnecting/reconnecting the unit jiggled back into action temporarily . try checking the loom for any breaks?

[Stjepan]

after carefully reading I am still not sure are you talk about OUTSIDE temperature sensor ? ambient is internal cabin temperature but since you mention radiator fans I am prety sure you talk about outside..that sensor is in area of front bumper near left foglight or behind bumper space in front radiators..sometime senzor is fine wires are coroded...this outside temp.you can also see in engine ecu,in climatronic,in dashboard...dont have schematic on this laptop but I belive sensor is hardwired to climatronic only,but sensor value are spread out via CAN bus network to every modul who is interested..when you disconect clima modul you brake CAN comunication between modules so they reseted on first ignition ON status..I dont belive its CAN faults,you just need more time to investigate and compare temp.value of that sensor in ALL car modules..IF they are same then sensor and 2 wire from it are fine..but Iam prety sure its wire/conector/sensor itself..climatronic is modul in clean enviroment relativly stable temperature no reason for fault on measurins inputs...on the other hand sensor is in bumper,wires rubing on chasis,small ****y conector in weather conditions.....

[Juka]

I didn't want to reply earlier until I got more data - so I played around with Climatronic diagnostic mode - tracking the bumper sensor (position 05) and fresh air intake sensor (position 06) and the calculated temperature from those two sensor that is shown both on the dash and the climatronic panel (position 04).

 

What I can see - both sensors work and seem to show correct temperature (maybe the fresh air intake is a bit on the high side, but it's near the engine and all that...). The conclusion is the calculated outside temperature is the one that is stuck for about 5-10 minutes into the ride.

 

https://photos.app.goo.gl/VZs936eN7bBy52CD7 - cold start measurements - all seem to be in order.

https://photos.app.goo.gl/2qAmYVPZZqH1YENp7 - warm measurements - unfortunately I didn't catch it, but when I fired up the car the temperature was 15°C on all sensors, after leaving the garage both "live" sensors rose to actual ambient temperature, but the number on the dash was still 15°C. Then all of a sudden just moments before I started recording it displayed the correct temperature...

https://photos.app.goo.gl/pwF7qPp2JzoxfUCHA - here is where I caught it acting up after a ride, you can see all sensor showing completely different (higher) temperatures than the one that is shown and stuck

 

This leaves me puzzled and I'm still leaning on that my Climatronic unit is acting up, and from the research I've done, it's not uncommon that they fail in this way... The thing is I got the car a few months back when it was cold, and it has always shown correct ambient temperature when cold outside. Only now when it's warmer the only pattern I can see that ~15°C is it's breaking point, if it's colder outside measurements work flawlessly, if it's hotter it gets confused and irraticly shows the correct temp, even though both sensors work...

 

When I get the time, I'll disable one of the sensors and see how it "failsafes" itself. If anyone experienced similar behaviour I'd be happy to hear how they solved it.

 

 

[Stjepan]

NOPE...Iam prety sure that temperature reading in dash is ONLY data from bumper senzor....AC intake temperature senzor have nothing to do with this display....maybe Iam wrong cause not a skoda expert..but most vw car work as I describe...

electronic input in clima modul have some "window"..will try to explain on my tarzan english

IF climamodul see that resistance is less then 600ohm it will display - 20

IF climamodul see that resistance is more then 2000 ohm it will display +45

that is working window for that modul..from 600 to 2000 ohm

so if resistance is inside this 2 values climatronik means all is fine I can show some calculated values..for you its time to investigate..is value on display MORE then real or LESS then real when this hickups hapens..one wire to sensor is GROUND another is signal..if this signal wire somewhere rubs on chasis then it will ADD resistance so dispalyed value will be MORE ..IF conection is bad then display will show less..we dont speak about broken wire IF is broken then you will easy dtermine where..this is situation sometime...

send me part number of climamodul..IF I have it I can send you for few days to test on youre car..but Iam sure modul is fine..Iam not telling you change blue/brown wire..just try to teach you how this crap in modern cars work..it is same story in all vw group

 

 

[Juka]

Quick update https://photos.app.goo.gl/qSoWjoAT8eCELYQ17 - again I caught it stuck, so while the fresh air (06 line) and bumper temp (05 line) show real time temperature, the display temperature (04) is stuck at a value on startup. This was at least 15-20 minutes into the drive, then as before it suddenly "unstucks" and jumps to the actual ambient temp but I'm not sure how accurate it is (kind of dangerous driving and playing with climatronic diagnostic during driving :-S )

 

[Juka]

Another update - the car was actually at @Stjepan for diagnostics and it was confirmed the climatronic unit is acting up. For some reason it just reads jibberish from the sensors (which do work well) and gets stuck.

 

The good thing is that the weather is now mostly warm and I seldom notice it being stuck. It's the transition period of 16~17°C that makes it stuck for a long while. It seems if it starts anywhere above and lower than that temperature the climatronic works nicely.