J808 Regulating flap

Living with a Scirocco 1.4 TSI 160 (118kW) – Part 3, Supercharger Bypass Valve (P10A4 Fault)

Sometime last year I was having problems finding a spot in a carpark so ended up sat in the car with it idling for several minutes and when I went to pull away the engine warning light flashed on almost immediately – not something anyone wants to see!

For the rest of the drive the car would mostly work ok at low engine RPM but the engine all but refused to go above approximately 3000rpm which is around the RPM the turbo takes over from the supercharger on this engine and the supercharger is disengaged by its electronic clutch. The curious bit was that at hitting the cut off there was a sudden loss of power at that RPM rather than it staying consistent and just holding an RPM limit suggesting it wasn’t a limp mode as such. My initial suspicion was that the turbo wasn’t spooling up so whether the wastegate was stuck open or something I didn’t know.

Luckily I bought VCDS which is an excellent tool for diagnosing and performing adjustments and if you do a lot of work on VW’s well worth the investment so I hooked that up to see what fault the check engine light was actually reporting and saw the following :

A quick Google of the code P10A4 identifies specific air regulating flap in question but this could also be found by a brief search of the engine bay – there aren’t many flaps in the intake! VW refers to this part as J808.

Image of the TSI160 engine with intake flap highlighted

What this flap actually does is when the supercharger disengages the flap opens providing an unrestricted flow to the intake of the turbo. Obviously if this doesn’t open when the supercharger disengages suddenly the air supply to the engine is closed and you get a massive power loss. You can see what’s going on in the image below which is taken from VW’s manual for this engine – SSP-359. This isn’t a workshop manual but does explain the design and behaviour of this engine in a good level of detail.

There are quite a few guides on how to replace this part such as using the one at workshop-manuals.com . This is an excellent resource but I do recommend using an ad blocker before going there as there are so many ads it’s very annoying otherwise!

My approach to get at the flap was to start at the airbox end and disconnect all the lines going into the intake tract (there are many in all directions so carefully work along it). Eventually once everything is detached you can undo the three long screws which hold the intake pipes on either side tight against the flap and so hold it in place. In my case I ended up detaching the section of pipe after the flap as well so I could lift the whole intake pipe up to get access to the bottom screw nearest the engine as its very awkward to get at otherwise.

Anyway as usual I didn’t want to replace the part if I could avoid it and luckily I found some comments somewhere saying the problem was caused by oil weeping from the intake into the flap unit clogging up the motor so I wondered if it could be cleaned because fundamentally there’s very little that can go wrong inside as they are basically just a motor. Luckily at this point knowing this was likely the problem I figured I couldn’t make it any worse than dead so started trying to work out what was going on.

So looking at the casing of the valve I came to the conclusion there was a simple gearing mechanism inside but based on the space between the clear position of the motor under the curved housing the likelihood was that the gear on the motor itself was small and so I could not explain why there was a significant large area in the housing below it which would likely be a handy cavity with no obvious purpose. The problem being caused by oil makes sense – the motor sits in the bottom of the housing which is underneath the intake pipework so any oil leaking into the housing would pool around the motor. I think the leak is through the spindle bearing for the flap.

So I came up with a plan which may be apparent already because I neglected to take any “before” pictures. I didn’t want to cut the unit open because even though the two halves appeared to be screwed together it looked like the seam had been sealed in some way (presumably part of why oil gets trapped inside) and while nothing appeared to be spring return I really didn’t want to risk it. So I decided to drill a small hole into the extra casing I identified earlier by using the casing as a guide as to where the gear and so end of the motor was. I then carefully drilled a small hole approximate 4mm in the casing and indeed there’s clear space behind this area.

My plan was basically to just flush the inside out with brake cleaner to remove all the oil residue so the hole was just a little large than the straw on the spray can. Sure enough on blasting some into it immediately the predictable brown runoff started pouring out. Another interesting thing happened as well – some residue started to run out of the seam inside the intake passage suggesting this isn’t sealed from the internal workings and in fact the seal on the unit is only on the very outer edge if the housing which may well explain the leaking issue! anyway several passes with brake clean and sloshing it about inside to rinse out as much as possible (I recommend just keep replacing the brake clean until it runs out clear) and it should be ok again hopefully. At this stage you might want to spray a small amount of lithium grease through the hole onto the gears for longevity but if you do just keep it small so you don’t just end up fouling everything with that instead!

Next, make sure the thing is totally clear of brake clean! I held mine under a hot air hand drier for about 10 minute to make it hot enough to drive off all the vapour then left it out in the sun for about half and hour. The last thing you want is a it catching fire!

The final thing I wanted to do is cover up the hole, particularly now knowing the intake wasn’t sealed from the innards. To solve this I tapped the new hole out to M5 and carefully checking the clearance I had behind the cover I put a short button head in place that wouldn’t foul the motor drive gear. Hopefully this also means If I ever have this problem again cleaning it should be easier. You can see the new M5 button head below.

After putting it back into the car I used VCDS to clear the fault code and so reset the engine warning light and took it on a test drive to confirm everything was fine. I think in total this took me about three hours but I was figuring it out as I went so you could probably do it in less.

While this was done during 2020 and so I have been using the car less due to travel limitations and working from home I can confirm that now five months later the car still works well and I have had no further issues following this repair.

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