2010 F01 740i Wet rear left footwell. No air from rear left foot vent.

[Eddles]

Hi all,

My F01 740i with 78k miles has quad-zone climate control. A month ago, I discovered the carpet for the rear left footwell was soaking wet. It would splash when gently slapping the carpet. I used a wet/dry vacuum to suck it up, and I sucked up like 2 - 3 litres of water. It felt a little greasy and strange, but the carpet was clean. I used a hairdryer to dry it out. Everything else is bone-dry - the door, the seats, the wall carpets, the front footwell, etc. I used a hose to check the sealing of the doors, and they're solid. Despite setting the rear left fan to maximum and directing it to the footwell, no air would come out of the vent. The same setting for the rear right worked perfectly, and warm air came out of the foot vent. So, I suspected the rear left footwell ducting was flooded with water and decided to use a borescope to double-check at some other time.

A few days later, it's damp again, but not as bad.

Recently, I got a "low coolant!" error, and I filled up the coolant. I didn't think much of it.

Today, I finally got time to put a borescope through the rear left footwell vent grille and discovered a heat exchanger within the ducting for the rear left footwell. Looking at RealOEM, I believe this is the electric pre-heater, as evidenced by this photo in this e-bay auction for an electric pre-heater. The ducting looks pretty dry, however. The borescope is a cheap Chinese special, so the quality isn't excellent.

Considering the low coolant error, I wonder if the heating system is leaking into the rear left footwell, but I doubt this is the case, as there shouldn't be any heating lines from the front to the rear.

Am I on the right track or barking up the wrong tree? What should I look at next?

Thank you!

[M_Bimmer]

Originally Posted by Eddles

Despite setting the rear left fan to maximum and directing it to the footwell, no air would come out of the vent. The same setting for the rear right worked perfectly, and warm air came out of the foot vent. So, I suspected the rear left footwell ducting was flooded with water and decided to use a borescope to double-check at some other time.

The air flow for the rear floor vents, in the 4-zone temperature HVAC system, are controlled by stratification flaps on the air box under the front dashboard.

As you noted, the floor vent has both a heating element and a temperature sensor.

The ideal path forward would be to run ISTA to look at what codes have been set on the HVAC system (IHKA = A95 or the FKA = A39, the FKA is a slave to the master IHKA ECU).

When using the rear floor vent, the temp sensor is used to regulate the rear floor stratification (air flow).

What you could do, is lift your front seat as high as possible, peel back the carpet on the right side of the vent, and disconnect the connector to the temp sensor. The other connector is for the heating element.

Make sure there there is no water inside the temp sensor connector, and if so, remove, and reconnect the temp sensor.

Test the system again.

BTW, the vent is held in by a 10mm plastic nut, then the assembly slides out from underneath the carpet. I think the only way to get to the nut is to remove the front seat, and in order to peel back the front carpet section, the bass speaker cover will need to be removed.