2000 A6 175K miles. Instrument cluster temp gauge started acting flakey, going from cold to normal, to cold randomly. Then after a week, always showed cold. Accompanied by code P1296. replaced the black CTS with a green one and cleared codes. Took a few 30 minute trips and the code is gone, but temp gauge in instrument cluster is still stuck on cold.

Using Vag-Com, looked at coolant temp via OBD-II generic mode - looks fine. Also looked at it by selecting instrument cluster group, advanced measure blocks, and that temp looks fine as well.

Seems like too much of a coincidence that I'd have developed an instrument cluster problem with the temp gauge at the same time. Read an old post where someone said the reason the CTS has four wires is that two send the reading to the ECT and two send the reading it to the gauge. That seems odd (you'd think the ECT would control the gauges), but if so, maybe replacing the CTS caused one of the gauge-related wires to have a bad connection.

Other posts mention the other temp sensor near the bottom of the car, but that it affects the fan speed and not the gauges.

In another post someone mentioned making the gauges move via vag-com, but I'm thinking that's only for newer cars than mine, no?

With the vag-com showing good temps I think the engine will be fine, but am pissed the temp gauge doesn't read anymore. Then again, I've never done anything based on that gauge in 13 years anyway. Would be nice to have advanced warning though if I'm about to overheat. Anyone have any thoughts? Thanks

 

First of all, for any of you who bothered to think about this post, apologies for a silly mistake. I got P1296 (coolant temp sensor issue) and then for the first time really started paying attention to my temp gauge and noticed it jumping from normal to cold and back at various times. Then I replaced the CTS, the code went away, but no change to the gauge I was looking at. It turns out that the gauge that caught my attention was actually the oil temp gauge, not the coolant! So, mystery solved regarding coolant temp - both the gauge and vag com agree it is fixed and temps are normal.

I guess it's pure coincidence that I also developed a oil temp sensor problem at the same time - really strange! Although a few weeks ago it would sometimes show correctly on the gauge, now it is pegged at cold. Vag Com sweep test confirms the gauge works. Vag Com constantly shows 155 C even when the engine is cold (instrument cluster, adv meas, display group 50). No idea why that doesn't peg the gauge at medium instead of cold. So I guess I should just ask my mechanic to replace the sensor at my next oil change and see what happens. Sound right?