2012 Jetta Sportwagen glow plug light and check engine light for split second

[EHoullahan]

So I’ve been having an issue with my 2012 CJAA where the car will loose a bunch of power then the glow plug light and check engine will turn on and off in a split second. If the car is idling it will bog and shut off. When driving it will jolt and seem to be in a limp mode for like 10 seconds then go back to normal. I can hear relays clicking under the dash so I pulled the panel off and found the bottom left two smaller relays(646) would click off and right back on. Replaced the relays and didn’t change a thing, still does it. Does anyone know what these relays are for, couldn’t find a diagram for a sportwagen. Doesn’t throw any codes, just comes on and goes right away. Very random. Anyone have any ideas?

 

[EHoullahan]

Have you scanned with a VAG scanner like Vagcom?

Yes. The only codes it had were for the plate lights being out because of them being led and one of the marker lights.

 

[EHoullahan]

FullSizeRender.MOV

• EHoullahan
• Jul 10, 2024

Cjaa cutting out. Have to idle high to keep it from stalling.

 

[Tuheeden]

With VAG running, you should be able to catch the codes when it happens. Very unusual not to have any pending codes.

 

[wonneber]

Yes. The only codes it had were for the plate lights being out because of them being led and one of the marker lights.

Did you scan ->before<- turning the key off?
Some codes reset when you turn the ignition off.
When I was having boost problems with my 2003 JSW going into limp mode I got good at stepping on the clutch, turning the ignition off for a few seconds, back on, and slowly letting the clutch up.
All this at 70 MPH (US) or so.
After I starting giving the car an Italian tune up daily.
I still do that with my 2014 JSW.