It usually did this when it was hot.
There are several potential causes of this problem such as battery and alternator issues, and a faulty ABS module is another possibility.
We diagnosed a fault with the ABS module on this Commodore by waiting for the problem to happen and then simply hitting the module. The dashboard lights would change when the module was hit so that was a good enough sign that it was the problem for me.
Fortunately, unlike on some cars, you can replace just the electronic part of the module without having to disturb the brake lines and without needing any reprogramming.
You must find a module with the same part number as yours. Unfortunately that part number is on the bottom of the module where it's not easy to see unless you remove it. The modules are usually referred to by their last three digits and this is one way you can search eBay for a replacement. For example, ours is a "485".
To replace the module you need to disconnect the top connector, which is done by sliding the clip on the side of the connector towards the engine until the plug lifts up.
Then there are six Torx screws, some of which are a little hard to get to and you may need to lift the whole module up a bit to get access to some of them. The module is held in place by the two 13mm nuts on each side which just need to be loosened to lift the module up.
You may find it easier to unscrew the cruise control module (three 10mm screws) to get access to one of the 13mm nuts.
The brake pipes have just enough flexibility to lift the module and get access to all of the screws. If you lift it up too high the rubber support underneath may fall out of position, and it is a little difficult to put that back in place.
With the six screws out the module just pulls outwards and then you will find another connector at the bottom that can be unclipped and removed.
Installation is just the same in reverse.
You can buy aftermarket units for $600 or more, reconditioned or exchange units, or just a second hand one from a wrecker like we did, which cost around $150.
I did actually cut the old part open to see if I could fix it myself but didn't see anything obvious.
If you need to, the car will run fine with the ABS module disconnected until you get a new one. But keep in mind you won't have working ABS, or traction control and cruise control if fitted.
Since replacing the module we have noticed the engine actually runs smoother, and suspect that the engine computer was being disturbed by the faulty ABS module.
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