B7 S4 Coolant light issue

[Scottish Burro]

A few weeks ago, I replaced the coil packs and plugs on my B7 S4 convertible. In doing so, I snapped the ridiculously fragile plastic upper coolant hose located next to the passenger side coil pack wiring harness. I found the replacement hose assembly online for over $200, which seems outrageous, so I purchased the same diameter (3/8") high pressure fuel injector hose. I purchased the replacement hose coupler (from Europa) located at the front, off the top passenger side of the radiator, and installed both this past weekend. I had purchased the Audi G12 coolant from the dealer and replenished approximately half gallon into the expansion tank. I read on this site about the need to "bleed" air out of the coolant system, so I removed the cap off the expansion tank and ran the car with the heat on high and got the temperature up to normal. I could see the coolant circulating into the expansion from the upper rear coolant hose. The red coolant light on the dash still would not go out. I let the car cool and tried again, and the light remained on. I tried the same bleed procedure as above, with the same result. No coolant is leaking anywhere and the coolant level has stayed close to the "max" level. At this point, I'm not sure what I should try next to clear the coolant light. Is there a sensor that may have gone bad? I'm suspicious that it might be sensor that would go bad at the same time that I break the upper hose.. Any thoughts? My next step is to take it to the mechanic, but would rather not waste the time or $ if there is a possible simple fix that I don't know about or that I overlooked. Thanks.

[VinnysS4]

did you damage the wire that plugs into the bottom if the expansion tank?

[VinnysS4]

it may be different, but when i removed the rear drivers side coil, there wasnt much room between the coil and the tank and i unscrewed the expansion tank to get enough clearance to remove the coil. Have you bled the system the proper way through the heater core hose?

[Brettannica]

Might be the Coolant Temperature Sensor (Green Sensor/Black Plug) located behind the intake manifold along the solid coolant pipe at the rear of the block.
As well as doing my oil check valve/valley pan gasket/oil filter housing replacement, I also have the three beeps at start-up, my coolant light flashing, occasionally my thermo fans running and no coolant leaking. I had the car scanned and this is the culprit.

[Scottish Burro]

Thank you both! Vinny, I did have to lift out the expansion tank to get at the last two coils, so I will double check the wire/sensor underneath. Can you explain how to bleed from the heater core hose? I've tried to find links for the DIY for this, and have not found anything specific to the S4 platform.
Brett, thanks for the heads up on that sensor as well.
You've both given me some things to check, which is better than where I was earlier. I'll let you know what I find.

[VinnysS4]

Ok to bleed the system, take off the rain tray. It is held on by the rubber molding. To the right of the battery will be the heater core hoses. They are usually covered by a fabric protector of sorts, if they are, just pull it back. The upper heater core hose has a small hole in it. You need to loosen the clamp and work the hose almost off..Basically until the hole is exposed to the coolant. Let the car run for a little bit, it will bleed itself. Put it all back together and you're done.

[Scottish Burro]

Vinny,
Awesome, thank you. I'll let you know the result. Thanks again for your help.

[Scottish Burro]

Thanks Vinny! it was the plug under the expansion tank. Light is gone and running fine

[VinnysS4]

Awesome! Glad I could help