Plenum drains blocked - a helpfull guide.

[techie]

As this seems to come up daily on the forum I thought i'd put together a little fact sheet if you like on the causes and symptoms of this very common B5 + B5.5 fault (does seem to happen more on 5.5's though I must say). This is an age old Audi fault that unforunately VW inherited when they nicked the platform for this Passat.

How the system should work -

Rain water runs down the windsceen and onto the scuttle, from here is in the case of the B5 collects in the plenum area (where the battery etc sits, a secondary bulkhead if you like) on the B5.5 it will run accross the plastic cover and down the sides. Either way water collects in the plenum and drains out of two small bungs/drains under the battery/servo (also above the steering rack) and out onto the floor.

How the system usually works -

Rain water runs down the windscreen and onto the scuttle, then runs down into the plenum and cant go anywhere because the drains are full of leaves and mulch. Water levels builds up and swamps the seals on the pollen filter housing and ECU box and leaks into the car. However the pollen filter seals are very poor and have been known to leak anyhow if ther eis a collection of leaves at the edge of the cover on the 5.5.

Common symptoms -

Alarm issues (going off randomly)
Bonnet open light not working (B5.5, maybe B5)
Central door locking not working
Indicators staying on (maybe just one side)
Brakes sticking on
Wet carpets
Condensation in car
Constant smell of old socks in car.

This can be a very expenive fault to put right. I have known cars to collect enough water in the plenum that they flood the brake servo with water which corrodes the back of the brake master cylinder, also freezes up in cold weather. A bit less extreme but usually the most common complaint is the alarm going off all the time or the oil level warning light will not clear when the level is topped up. The cause of this is water ingress through the pollen filter housing. Water runs down inside the car to the connectors at the A pillar. The back one which is a grey plug houses the wiring for the bonnet pin switch, this corrodes out and creates issues. Also the water runs down into the CDL ECU which sits under the carpet on the passenger side. Issues arise on the drivers side as water passed the ECU box or the bonnet cable grommet, usually a failure of the throttle pedal is the first sign of trouble.

These are all very common faults but they all can be avoided if the pollen filter housing is sealed properly and the rain guide hasnt been lost on top of the pollen filter and the plenum drains and plenum area are kept clean and clear of debris. To seal the pollen filter housing properly I use sealing cord (available from VW). Its like Dum Dum (for those in the know) on a roll, does the job perfectly but can be taken apart again if needs be. Silicone sealer however wont help in this matter.

There is a very handy how to here on this subject -

http://www.weirdlittlebiscuit.com/passat/leak

However should anyone be suffering some of these symptoms and needs some help I could repair for you and do a more indepth 'how to' for a very modest fee (compared to dealers anyhow).

[mycarsavw]

I compiled a guide on another forum, s'pose I could link that here when I find the, erm, link - if techie doesn't mind that is.

[techie]

No problem at all, we are all here to help.

[mycarsavw]

Link as promised;

Water Ingress and Solutions

[Ste_Nova]

bonnet open warning.... i've never seen that, and when i had oil low warning it was battery off for a night to clear it!

[strictlyVAG]

i did this last weekend and quite enjoyed it, lol

pushing my index finger throught all the goo was somehow pleasurable!







is this wrong!

[doobie]

Yes
Very

[ldavies93]

FYI: The sealing/Dum Dum tape is also known as Bitchumen tape, creates a seamless join out of bitchumen - I bought a roll from the local Volvo garage was about £11 at their hugely inflated prices but I've got plenty for other jobs now.

I found the VW advisory on the web somewhere and followed that but it basically said wrap the stuff round twice, seamless join, then squeeze it down by bolting the casement down onto it.

No water problems since Well apart from the door lock mech messing me about coz the window scraper separated Still thats another job for another day!

[BRIDGEY 20V T]

I had a quick look at mine today oops i had a duck flooting in my bulkhead so of cours by this time the weather being how it is it starts to pee it down so did a real fast bodge job an realeased the gromit for the heater pipes cause i cudnt get my hand under the servo but it did the job till a dry day when i can remove my battrey and tray and do it proper. i also checked my pollen filter why i was there flipin ek it was filfey cleaned it up for the time being but must get a new one

[g60dubster]

Think VW released a TSB sometime advising to pull the grommets out of the drain holes too...

[64 SPLIT]

yeah I just pulled both of my gromets out, cut out the flappy bits of rubber in the middle and replaced so there's no chance (or very little) of them blocking again

[Lee]

can we reach the plenum drain grommets from under the car? (I'm imagining a strange reaching up and delicately "milking" the sludge out type action... and just about making it seem easier in my mind than opening the plenum area up and so on as suggested....)

(that car's wearing a leather bandanna???) (look up)

[Lee]

oh.. those images change... oh well lol

[TDWEYI]

What a crackin bit of advice and photo tutorial
Did this last weekend and discovered a pond under the battery and alarm and master cylinder
the grommet under the brake cylinder is a twit to remove as a brake pipe goes through it, I just pushed a finger through the shite and woosssshh no more pond,. Cleaned up the general area flushed the remaining debris out. The battery was a **** to remove . Any way just off to cut down the neigbours sycamore tree for clogging up my plenum "Starts chainsaw

[richard s]

wife told me that water was dripping into passengers footwell yesterday so while i was looking for some ideas as to why i found this thread after thinking it was something to do with the inlet
i found for a quick job tonight before i got soaking wet that when battery was removed i could reach under the servo and i could just get my fingers through the battery tray enough to poke my finger through the sludge after that poured a couple of watering cans of hot water down and now have a good flow of water coming out
so cheers to the person who started this thread

[Lee]

can we reach the plenum drain grommets from under the car? (I'm imagining a strange reaching up and delicately "milking" the sludge out type action... and just about making it seem easier in my mind than opening the plenum area up and so on as suggested....)

this was a serious question..! lol

Okay then, what about using coathanger wire or similar to budge the sludge... without removing the battery... would that be feasible I wonder... only someone who's been there would know... I'm not lazy, I just hate breaking 50 per cent of the plastic parts I remove no matter how careful I am.. these things are not designed to be disassembled/reassembled...

[techie]

You can get one of them from underneath but its not easy as the grommets sit above the steering rack.

And if you do get one look out, your gonna get stinky and wet.

[rossmck]

Okay then, what about using coathanger wire or similar to budge the sludge... without removing the battery... would that be feasible I wonder... only someone who's been there would know... I'm not lazy, I just hate breaking 50 per cent of the plastic parts I remove no matter how careful I am.. these things are not designed to be disassembled/reassembled...

Mine was done (by Colin - thanks!!) with a ridiculously high pressure pressure washer without removing the battery! - When it was next in a VW garage (for damage caused by water ingress) they commented how well cleaned out it was

[J1MMY]

Mine indeed does smell of socks!

However the scuttle (plenum is a new name to me ) seems pretty clear. Also, the moisture seems concentrated on the passenger floor and under the seat. No moisture in the slope of the footwell. Is this likely to be the same problem or could it be a different yet well known one? The smell is DISGUSTING. I wish the weather was better, I could pull the carpets and dry them out.

[techie]

More than likely the pollen filter housing.

It wont feel wet down the 'slope' as the water runs behind it and the carpet is very thick there.

[J1MMY]

Nice one Techie

Pulled the battery out yesterday and cleared the channels which actually weren't blocked too badly - the area under the battery was bone dry. The pollen filter was a different kettle of fish - the rubber seal was split and the sponge sealed totally useless and half falling into the blower. Didn't have any of the prescribed sealants to hand so doubled up on double sided glaziers tape (used for putting cosmetic bars on windows) which will do unil I get to a windscreen place for some of that evil double sided sticky rubbery stuff (yeah technical term ).

Now then, how do I get rid of the horrendous stench in the car?

[b5rockingthevdub]

just did mine after i found a pond in the back foot well behind the drivers seat, the drainage hole of the drivers side was well blocked,, fingers crossed after i dry it out it wont come back now. but the rear offside passenger door isnt looking sometimes on the first attempt but always on the second,,, would that be related to abit of electronics being moist,,, it stopped for a few weeks during the drier period we had a few weeks ago,, but now back in force(now its raiing most days). fingers crossed now ive sorted the main problem it should dry out and sort itself,, but is it easy to find and check it yourself?..

[grhdylan]

Just checked mine today....... 1 hole completly blocked, other one gunged up but still letting water pass through. I took out the rubber grommits completly to stop it happening again ...... i'll have to see if i get any engine smells in the car, if i do i will put them back in, i'm just hoping this way i can forget about cleaning them out every year !

[rossmck]

Both my rubber grommets were removed by my local VW dealer ... so i'm sure it wont cause any adverse effects

[Lee]

well I was fitting my front coilovers ... dropped a 13mm nut from the top-mount down under the brake servo . And searching for it I came across the small vw swamp ecosystem living at the bottom. And proceeded to carry out the only correct procedure.... shoved my finger into the clag... and "sploosh" the small amount of gunge fell out onto the block pave under the car. How satisfying! Couldn't find the other one under the battery though? But I did find the loose neg terminal... God one day I'll just go over the car and tighten everything up... I'm sure I'll find more loose things than at a brothel, for instance .