MarshallB

B7, coolant idiot light came on a week or so ago. Dropped at Audi for 85k service today, now they want to keep overnight to check it out (advisor mentioned a check valve, dunno if he meant the thermostat or not, is there a check valve somewhere, and if so where, and what does it do?). Fault info below.

Single fault and car is running fine, temperature dial on dash didn't budge when fault occurred, just over middle mark where it always is at operating temperature. Freeze frame says 72C, which I guess is a little low (particularly for driving at 92mph, though it was cold out, -4C is 25F).

Is the freeze frame temp the same sensor that the dash indicator uses? I am thinking just a glitch. Anybody disagree? Anyone know what the "fault status" value means?

1 Fault Found:
18613 - Performance Malfunction in Cooling System
P2181 - 008 - - Intermittent
Freeze Frame:
Fault Status: 00101000
Fault Priority: 0
Fault Frequency: 1
Reset counter: 255
Mileage: 135909 km
Time Indication: 0

Freeze Frame:
RPM: 3404 /min
Load: 95.3 %
Speed: 148.0 km/h
Temperature: 72.0∞C
Temperature: -4.0∞C
Absolute Pres.: 1010.0 mbar
Voltage: 13.843 V

Readiness: 0000 0000

MarshallB

This problem came back with the cold weather.

I did notice that temperature gauge dropped to about 1/4 one time after being at operating temperature (about half scale), so suspecting the temperature sensor, ordered one of those and I can see it at the back of the engine but sure looks like skinny hands and feel required ...

Also poking around found a TSB (C 19-05-02) indicating that engine warm up can be slowed by bad check-valve in hose between main and left aux radiator, but don't understand what a check valve would have to do with warm-up (a thermostat, on the other hand ...).

Now wondering if slow warmup can cause this fault to be thrown. In cold weather probably takes me 10 miles for engine to come to full operating temperature.

Anyone have any thoughts on my little problem?

Thanks.

s4master1

sounds like the thermostat is sticking open.
when this happens you drive at high speed and the air flow thru the radiator cools down the coolant
if you drive at slow speed is ok as the flow of air is less.