2001 TT Roadster 1.8L, 180 HP, AWP Engine, 52K miles, original owner. Intermittent false overheating alarm. Most commonly occurs shortly after cold startup. Eventually resolves itself if you keep driving. This problem has been with this vehicle for a while. It used to occur rarely but has become very common (occurs more than 70% of startups). No diagnostic codes thrown. During event (warning symbol, audible alarm, and temperature gage pegged to Hot) climate control diagnostic code 49c pegs to 121 degrees C. The cooling fans go to high and the AC is disabled (seems like a reasonable response to a true overheat). Initially replaced the engine coolant sensor(s) (G2/G62 in Bentley). No change in behavior. Partly out of frustration I whacked the top of the dash during an event. I was running the 49c diagnostic at the time and noticed the displayed temperature immediately dropped from 121 to 111 degrees C. When I hit the dash again, the temp dropped to upper 80's and stabilized. Pulled the instrument cluster to check for wiring issues, etc. One of the connectors was not fully secured (center one, not the one which carries the G2 temperature signal). Re-secured all plugs and tested the car without the lower dash cover installed hoping I could do some cable wiggling if the problem returned. Car ran fine without any temperature alarms, needle excursions, or temperature spikes shown via 49c. Hoped problem might be gone. After I re-secured instrument cluster and installed lower dash trim got a temperature alarm on next subsequent startup (“fixed”with a dash whack). The instrument cluster has some issues which I'm not concerned about (missing segments from center display and a temperature gauge that reads consistently high (not hot) even when 49c temperature is normal (87-90)). I'm suspicious of the instrument cluster, but have not seen any forum data relating to this particular failure mode (temperature spikes /alarms). I'd hate to drop money on a replacement or rebuilt instrument cluster and still have the issue. The car has a few other issues that I don't believe are related but: 1 ) Airbag alarm with un-clearable faults from most if not all igniters. 2) Intermittent (every other drive) Anti Slip Regulation (ASR) / Electronic Stability Program (ESP) alarm. DTC code points to issue with G200 lateral acceleration sensor. Looking for some pointers on the overheating issue as far as next step. I have not been able to identify any wiring issues in the area, but it's tough to see it all. Instrument cluster shock or cable movement appear to “correct” the problem but not produce it. Any ideas on how to narrow down problem or opinions as to whether it's the instrument cluster or not would be appreciated.

 

I had that overheat issue with my 2001 225. Gauge showed overheat and fans did not come on. Had it towed to a local shop that changed my water pump then determined it was the gauge, thanks. Found a rebuild place on ebay for 149. that fixed my cluster via fedex and had it back on the road in 2 days. That was 3 years ago and its been fine since.

 

I also have an 01' Quattro with a similar issue. There are several "quirks" with the instrument cluster which includes fuel gauge malfunction and the LED readout in the center -
the "information center" which has a mind of its own and goes haywire. At some point, I too will more than likely be sending my instrument cluster in for service.

Until then, here are a few helpful tips:

These cars are prone to overheat due to a design flaw. I know, really?

If your driving any distance, the quick and easy fix is to crank up the heat.
Yes, the heat. The "heat" for the interior from your HVAC comes from the engine/engine compartment. The cabin filter is used to diffuse the exhaust and other "vapors" from the engine and the outside fresh air intakes. The heater acts as a supporting "condenser/radiator" combination and will actually reduce the temperature from the engine compartment.

Another option, is to pull over and pop the hood. It is here where you can hear the cooling fans running. The TT has a sealed coolant system and does not have a radiator cap. Well, this is true for the 1.8 Quattro. I'm not sure about the 1.8 non-Quattro.

Keep a phillips head screwdriver in the car that fits the screws that secure the panel over the overflow bowl so the panel can be removed. Now, very carefully, slowly turn the cap on top of the bowl counter clockwise to release the heat a little at a time. As the water level increases near the top, start to tighten it back up. Do this a couple of times until you hear the cooling fans go off. Close the hood, crank up the heat and go. If the problem continues, take it to your mechanic or the dealer and or have it towed. DO NOT take a chance!

Hope this helps.

Best of luck.

Rudy