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Discussion Starter #1
Hi all have the dreaded intermittent above messages 1 day after Car service..... at startup only.

1) Have bleed the brakes with over 1L of new brake fluid using a vacuum system (just in case some crud or air or ?), Disconnected 12V battery 12.4V tested after drive 12.8V when the fault happened again.
2) Cleaned very carefully grounding point G117 which was clean showing no signs of corrosion & is a press hex fit on the Id - cleaned with contact cleaner and reassembled.

Logging in scanner shows no fault codes logged but brake assist is definitely not working when driving the car until I initiate clear fault code command and error messages clear, normal brake assist resumes.

Will just keep doing this till it is a hard fault vs intermittent as my only authorised dealer is way across town and I don't wish to waste futile money diagnosing an intermittent fault.
The other thing will be the horrendous costs to replace the x2 relevant modules if deemed faulty.
I'll have to find out what is covered by Holden Australia vs Australian consumer law for products - I know GM in Australia avoid doing the right thing when it comes to abiding by local consumer law.
I don't have $1,000's sitting by just to do unexpected major brake component replacements on a 6 year old Volt.

As I'm the only driver, I just keep it going till it fails permanently with knowledge I may have to press brake pedal very hard just on hydraulics and or activate electric park brake.
Been happy in the past with Forward braking, but have had the Volt with extremely weak / pedal sinking braking in reverse on a forward incline that took me by surprise many times.
For this reason I never lend the car to anyone to drive.

Love my Volt, but am getting very tired of serious expensive faults in the past year.... and I have less than 30K Km on the car over 6 years. Car is parked in a dry garage - so no it doesn't see any corrosion like some do in North America or Europe.
 

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Discussion Starter #3 (Edited)
Check the abs rings
please explain, ie missing teeth, loose etc. I have heard on later models damaged wiring to the ABS can produce this error. Will put it back on the lift and do a quick check.
Update ....
LOL this model is one with magnetic plastic abs rings in the hub that are known to crack and fall out.
The front ones I can see from inside through a gap, the rears I had to pull the wheels and remove the sensors.
All mine do not have any chunks missing but not easy to inspect if they are cracked & spun.
Still could be a faulty sensor or wiring harness though.
Traced & checked all the wiring and all is in perfect condition and connects are clipped in all the way.
Guess I keep driving it till it gets constantly worse then it should be easier for the techs to diagnose.

Interestingly it never faults while driving it does so on start up stationary.
I've tried shutting off with brake pedal applied or without, still is random.
Service Stabili Trak warning comes first then -
Service Brake Assist
Red Brake Fault light, Amber ABS and Stabili light also display on panel.

Strangely when cleared via OBD2 I can drive / brake normally give it full throttle on a corner and it activates Stabili track (ABS)
All perfect - never faults when cleared and driving.
Only does so at stationary start up.
Must be something stuck or faulty sensor reading on power up.
 

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Discussion Starter #4
Just to update after numerous drive cycles today all appears well after finding old fluid in main reservoir again.
Put another 0.6L of Dot3 through it but this time while having the Mitivac pulling vacuum on each wheel nipple one at a time,
I pressed the brake pedal to the floor - 4 times for each respective wheel bleed *
*Do not let the brake fluid run low while doing this - two people job.

It appears to have freed up what ever was causing the intermittent error codes on start up.
If you don't see an update it has been success otherwise I will keep you all posted.

Best to let the dealer do brake fluid flushes as they can cycle the system (if done properly) and put fresh clean fluid through it completely.
The Volt system is very complex and apparently has many inbuilt miniature filters but who knows if miniature dirt will get through hence cleanliness is most important best use clean lint free cloth when opening or servicing the system.
Clean with separate cloth etc. before opening fluid cap for service.
 
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