98 Passat - Probs with Coolant Temp/Level Light

I have a 1998 Passat GLS with the 1.8l four cylinder turbo engine. Car has 67k miles on it. The problem is that when it gets a little cold (and we're talking CA weather here, so in the over all scheme of things, I'm talking about pretty mild weather), the coolant temperature & level warning light comes on, the audible alarm plays for a while, then the light stays on for the duration of the trip. The problem is intermittent. The coolant level appears fine (when the engine is cold, it's about half way between min and max on the overflow tank), and the car's been checked out by the dealership. They didn't find any apparent problems, and replaced the temp sensor (I think; I'm borrowing the car from my in-laws, who are traveling). The problem went away for a couple of weeks, then came back. Engine starts and runs fine even when the problem is happening, there's no evidence of coolant leakage under the hood (i.e., that white crusty residue) or in the oil, the coolant is a bit dirty, but looks OK.

Any thoughts on what could be causing this? Thanks!

Sorry don't have any good ideas about this, but I have been experiencing almost identical problems since my 1998 Passat was two-and-half years old (purchased new). Dealer couldn't find anything after $50 of diagnostics. My coolant light comes on at cold start in morning when ambient temperature is below about 55 or 50 F. Then after the engine warms up it goes off and does not come on again until the next cold start. Doesn't do it at all in the summer, but does it all winter (here in Seattle). I have read somewhere that this is a problem with the coolant level sensor in the expansion tank, but it hasn't concerned me enough to spend any more money on it, so I've been living with it for years. It doesn't affect drivability in any way. If you discover anything, let me know.

hi. i cant help you in any way, but i also have a 98 passat gls 1.8t and i have the same problem. about a year ago i only had the problem occasionally, but for the past 6 months at least the light stays on all the time. just flashing. the temperature remains normal, the gauge remains normal..the light just flashes. with all the other problems ive been having with the car, i figure this one is just a nuissance and nothing more. after reading the thread, it seems we're not alone, eh?

strange issue to have, though

Unfortunately, I had the same problem under almost the same circumstances. I was told that it is yet another problem in the control module, which will cost about $1200 to fix. (Coincidentally, this is what I had to pay to fix the ignition control module when it went bad. Each part of the module is outrageously expensive to replace.)

You are correct, there is nothing mechanically wrong with the car, and after driving with the identical problem for two winters, I haven't detected any bad effects.

Alright this will be my first contribution to the Volkswagen/Audi world. Here is the story...

Before I begin, this fix is time consuming, aggrivating, and requires the utmost paticence. Anyhow, 01 Passat 1.8t AWM, non-corrosive environment. Helped a family member pick it out approx 1.5 years ago. From word go coolant level light flashing, verified false alarm. Told them to purchase new coolant tank installed, still same problem then, the vehicle's fuel pump relay started acting up, along with various systems. That told me to start looking into ECM,CCM,Grounds. As I started diagnosing systems 1 by 1 could tell previous owner or someone had already been where I was going up to the ECM. Pulled CCM unwrapped wiring harness all splices were pristine along with CCM. After viewing electrical diagrams for 1 day discovered that seemingly seperate systems were actually related. Here is the "FUN"? part, removed interior from instrument cluster back to rear seats. After doing that started looking at ground points one on each B-Pillar one on each A Pillar one under center console, and one chassis to battery. After pulling ground nuts discovered that instead of using bare nuts they were painted with the body, leaving a 1/8" +- ring of paint buildup around the edge of the contact side. maybe when the car this is okay, but after a few years where it was just pushed into the body humidity creeps and leaves an oxidized surface and now has to try and find ground through the nut with the paint buildup it can't. So what I did was take 100 grit sandpaper on a flat surface and sanded the ring of paint off completely. After reassembly, motor ran smoother, turbo more responsive, coolant level light quit flashing, relay quit chattering, and some other things that I can't remember right now. Sorry for the poor construction, not good at telling stories. Anyhow if someone else having similar multisystem malfunctions, and trys this let me know the results on your vehicle please. May have found the problem source for alot of ECM appering problems.
Next in post is a good resource for the B5, I know its russian but there are english docs
http://vwts.ru/pl_b5.html