Low Coolant warning

Since last week I am getting a coolant warning in the DIS. It happens about 5 minutes after a cold start and goes away after another 5 minutes. While the message is in the DIS the temp gauge stays at zero and when the error goes away it suddenly jumps to the actual temp. There is enough coolant fluid in the system and the temp does go to a perfect 90 degrees (celcius), so everything seems to be okay.

The dealer says it sounds like a faulty sensor (The car is booked for next week). Is the coolant temp sensor the same one as the level sensor next to the filler cap? I unplugged en re-seated that one but that hasn't helped.

Nah, it won't be a porous head casting. I am not losing any coolant, it looks like a false alarm since the coolant level is not dropping and the engine reaches a perfect 90 degrees.

Anyway, the car went in yesterday and they replaced the little expansion tank (there is a sensor in there). They said it was quite a lot work work too! Good thing I took the additional warranty.
Edit: CRAP crap crap... just got a call from the dealer, The repair is not covered by the extended warranty. WTF? Surely this is not a consumable part!

When I left for work this morning the coolant warning came on in the DIS again :-(. Looks like the new tank+sensor did not solve the problem. Somehow I knew this was going to happen. As far as I know the sensor in the expansion tank is a level sensor (basically two metal rods that stick in the fluid) and not a temperature sensor, while the symptoms indicate a temp sensor issue. Does anyone know where the coolant temp sensor is located?

I hooked up VAG-COM last night and two errors popped up.

2 Faults Found:
16502 - Engine Coolant Temp. Sensor (G62): Signal too High
P0118 - 002 - Lower Limit Exceeded - Intermittent
18359 - Radiator Fan 2 (V177): Movement Restricted / Jammed
P1951 - 002 - Lower Limit Exceeded - Intermittent

The car was in for a callback (some gasket in the coolant circuit) in January. I wonder if that has anything to do with these faults. I wouldn't be surprised if they knackered a plug or loom that carry the signals of both the temp sensor and the fan controller.

leggy said:

I used to get the coolant warning light come on in my A3 1.8t, it used to come on seconds from starting the car and would probably last a couple of minutes,although this would only ever happen in the winter,come summer it was fine,i used to just ignore it in the end.The first time it happened was panick stations,thought i had big problems cause the levels all looked fine.I had the local Vag specialist garage looked at it,he cleaned the sensor up that measures the coolant level,problem was solved although it did return about a year later,so like i said,from then on i just ignored it and never had a problem !

Click to expand...

The coolant level sensor is part of the expansion tank and they replaced the whole tank earlier this week. Despite the fact that I have extended warranty they are even charging me for it too! I hope they are not randomly changing parts and then charge me for all of them. I though it was a good dealer, but this is really putting me off Audi.

Car was at the dealer yesterday. They replaced the coolant temp sensor (G62) and one of the radiator fans. No coolant message in the DIS anymore, but when I checked with VAG-COM as soon as I got home last night I still found a fault. Maybe they forgot to clear it. Anyway I cleared the fault and everything seemed to be okay on my way to work today. I'll plug in VAG-COM again tonight. Hopefully the fault hasn't returned.

I have a gut feeling that they are replacing all these parts while the actual problem is actually something else. I find it too much of a coincidence that all these coolant related parts seem to fail a few weeks after work was done on the coolant system. It is much more likely that it is a problem with a plug/wiring/controller. I bet some coolant leaked into an electrical part the first time and now that corrosion is setting in it starts throwing all sorts of sensor faults.

Anyway, I hope I am wrong. Going to France this weekend so we'll see how the car holds up. I'll certainly be taking a laptop with VAG-COM and a bottle of coolant with me...

So far, so good. Maybe I've been a little too paranoid about the fault finding skills of my dealer. Several trips later and VAGCOM has not registered any new faults since I reset them when I got the car back from the garage. Perhaps the fault is actually fixed. As far as I'm concerned: case closed.

(Remains an issue of them invoicing me twice for some other work that was done at the same time. New tires & new brake pads. But that's another matter that I won't bother you with)