VDC intermittent fault

[rfesu]

sometimes totally at random (cruising on the highway, cornering, whatever) VDC will kick in and odd things happen.

 

sometimes it brakes, sometimes it cuts boost.

 

sometimes it does this with no evidence, but sometimes it also lights the VDC OFF, and sometimes both VDC OFF and check engine, but both of these conditions clear themselves very quickly and things are back to normal.

 

tires are brand new (problem seemed the same with the old tires)

 

i don't have a scan tool that will read the VDC error codes yet, but hope to get one, not sure the best thing to use. i tried connecting the black wire but didn't get any codes.

 

in the mean time, does anyone have any insight into what i could start looking at?

 

it seems there's not a lot of documentation on this early VDC system

[rfesu]

i found a very interesting thing while installing my boost gauge last night

 

on the right side of the dashboard there are three switches - fog light, headlight angle, and then a blank. the empty switch hole has a plug going to it.

 

i did a bit of wire tracing and found that it has connections to the VDC box, and while probing it i accidently grounded something - it blew the ABS fuse.

 

then i found this in the parts diagram.....image attached

 

it appears to be the same switch type as the fog switch

 

i wonder if maybe they intended to install a VDC switch there and decided not to

[rfesu]

so it turns out that ecm codes can trigger a vdc fault. i had a knock sensor code. the ecm seems to trigger the vdc module into a failure state before it even sets its check engine light... interesting behaviour. i triggered a code 66 after replacing the sensor (missed a vacuum line) and it killed VDC again. could not get any codes from the vdc unit at all.

i guess if we could reproduce that signal we could enable/disable this early vdc system at will although there could be a better way