P0638 and Air Regulator Flap/Throttle body Valve

Rigger007

Member
Joined
Feb 21, 2012
Location
Portland Oregon
TDI
2010 Jetta 6MT
Hey folks, I know TDIs don't technically have a throttle body flap, but it has a lot of names depending on whom you ask. My car just gave me a blinking glow plug light, along with a solid CEL, so I scanned it with VCDS and pulled a P0638 implausible signal code. I pulled the valve and cleaned it up, cleared the codes, but they came right back. I took it to the dealer and they confirmed I needed a new valve. They're saying the valve needs to be programmed after replacing. Is this something I can do with VCDS?

I can't pay a couple hundred in labor to replace a part I just pulled, cleaned, and reinstalled in less than 45 minutes. Not to mention I consider any money spent on this car now to be money wasted.

If I can program it myself, is there a write-up on Ross-tech or somewhere?

Please advise, thanks folks!

Tim
 

meerschm

Top Post Dawg
Joined
Apr 18, 2009
Location
Fairfax county VA
TDI
2009 Jetta wagon DSG 08/08 205k buyback 1/8/18; replaced with 2017 Golf Wagon 4mo 1.8l CXBB
Just looked at this. I think there is an adaptation pull down on VCDS

but it could be that you can put the new valve in and it will make peace with the car on its own. the part has not only the intake throttle valve, but a position indicator.

The J338 is discussed in the self study guide on page 54

http://www.natef.org/NATEF/media/NATEFMedia/VW%20Files/2-0-TDI-SSP.pdf


if that indicator is broke, all the cleaning in the world will not fix it.

why don't you want to spend money on the car?

(and by the way, you need this valve for the DPF to regenerate, so you might want to park it or fix it.)
 
Last edited:

Rigger007

Member
Joined
Feb 21, 2012
Location
Portland Oregon
TDI
2010 Jetta 6MT
Thanks Mike. I ordered the part and will see how it goes.

I'm not crazy about spending any money on the car because of the emissions issues. I've actually had the DPF replaced, EGR valve twice, constant issues with the emissions system on this thing during the last 50k miles. Luckily that was all under warranty. I'm over 110k now, and unless I just gut the exhaust and all the emissions the car is too expensive to maintain vs its value, which thanks to VW is now zero.
 

Bravo19r

Veteran Member
Joined
Jan 11, 2010
Location
Burnaby, British Columbia
TDI
Y2K4 Jetta Variant TDI (RIP), 1996 B4V 1.9 TDI (Re-Homed), 2010 Jetta TDI Highline
Speaking of this fault, this happened to me the other day. 64k miles on the clock.

Just waiting for the long weekend to look at it.
 

meerschm

Top Post Dawg
Joined
Apr 18, 2009
Location
Fairfax county VA
TDI
2009 Jetta wagon DSG 08/08 205k buyback 1/8/18; replaced with 2017 Golf Wagon 4mo 1.8l CXBB
If you plan a DIY, I found that it is a little tight to get the three torx screws that hold it together. a 1/4 inch drive ratchet and a couple extensions did the trick.
 

odeanono

New member
Joined
Oct 29, 2017
Location
Seattlelish, WA
TDI
10 Jetta 6Spd CJAA/06 Jetta DSG BRM
Hello All, I also just popped a check engine and flashing glow plug showing a P0638 pulled at an O'Reilly's. It is on my '10 Jetta CJAA. But I made it to 265K first. It runs fine and the part doesn't look too difficult to pull and clean but a Y_tuber said if you don't unplug the electronic connector then I won't have to recalibrate it. I assume this is what everyone is using a VCDS for, which I don't have. It would be a lot simpler to clean if I pulled it all the away out. Does anybody know? Also where can I get these gears inside if the teeth are bad? More time than money ya know!
 

Strong Malt

Member
Joined
Dec 19, 2013
Location
Utah
TDI
2010 Sportwagen
Hey All, I have a 2010 JSW TDI, 176k miles. Recently threw the P0638 code. After watching a few youtube videos I removed the throttle body, cleaned it thoroughly with carb cleaner and re-installed it. Code, engine and (blinking) glow plug still there.

Any updates from anyone on the best resolution here? Thx much.
 

BrettM

Member
Joined
Jan 29, 2018
Location
Camp Point, IL
TDI
'06 Jetta, ‘13 JSW
Same issue here on my 2013 JSW. I’ve found a lot of questions throughout the internet but the only suggested solutions have been to attempt cleaning or to replace the throttle valve. When those don’t work for people, the conversations stop. I’ve cleaned mine but don’t want to replace it if that’s not the fix.
 

hertdi

Member
Joined
Dec 10, 2018
Location
Puget Sound
TDI
14 JSW
Same issue here on my 2013 JSW. I’ve found a lot of questions throughout the internet but the only suggested solutions have been to attempt cleaning or to replace the throttle valve. When those don’t work for people, the conversations stop. I’ve cleaned mine but don’t want to replace it if that’s not the fix.
Any updates?
 

Michael B

Member
Joined
Jul 11, 2018
Location
Utah, USA
TDI
2010 Jetta TDI
Any updates?
BrettM is not me, however, my 2010 jetta tdi was getting the same code. p0638. glow plug light would flash. the MIL came on. I wanted to try cleaning it myself but eventually the diesel particulate filter came on and soon after the car went into a limp mode. I HAD to take it in at that point. They weren't able to clean the valve and force a regen, so it needed replaced. After the replaced it, and driving in the right 2500-3000 RPM for about 4 hours, the regen was able to clean out the DPF.

Since it was replaced I have had some sort of electrical issue off-and-on. Not sure it's related, but on occasion the TCM stops communicating with the ECM and the car won't start, and if it does start, doesn't let me change gears (P, N, R, D, and S all just flash). I open my hood, wiggle some electric cables, and the car works again.I'm still trying to figure out why it happens sometimes.
 
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