Water under carpet of VW Passat

In this weekend’s show a caller had water under the carpet of a VW Passat.

This problem is very common to these cars, and it will cause very expensive electrical damage, not just mildew. About 4~5 gallons of water can actually be held under the carpet without the owner having a clue it’s there. There are two computers mounted under the carpet which will be ruined in short order if the water is not drained ASAP.

The drain plugs in the floorboard should be permanently knocked out to make sure water drains and will not accumulate. The enclosures holding the CCU and TCU should also be opened and drained or corrosion to the computers and wiring harness will continue even after the carpet is dry.

The source of the water could be from one of three places - sunroof drain lines, pollen filter, or under the ECU (plastic box under the hood near the windshield). The drain plugs under the battery should also be permanently knocked out to insure water does not collect in the cowling area, which is what causes the water to find its way in under the pollen filter or ECU.

I can’t buy that. Be observant and if water gets in there, look for and correct the cause is far better than just leaving a hole in the floor.

Really water or antifreeze? If antifreeze-then most likely heater radiator to heat the car inside is leaking.

I suffered with this probably repeatedly with my 2001 Passat Wagon. The source of the water was definitely the ECU. The cause was the drain holes clogging with leaves, twigs, etc. no matter how frequently I cleaned out the ECU. The drain holes have large rubber grommets that cover the edges of the drain holes but also act as perfect debris-collection dams. After I removed the grommets the problem has never recurred and I have never had to clean debris from the ECU.