ABS light comes on......... Sometimes.
 

What would be the cause of this gremlin?

usually it happens when you hit the brakes hard, as if in collission avoidance maneuvre... no biggy, system is working as designed...

Oh Im talking about. Randomly every other week or so usually on my way home from work. I really havent done any of the above mentioned.

I dont know if its a coinsidence of the hot weather but seems to happen when AC is on too..Maybe.....

hmmm... if the system is malfunctioning, then you need to gather as much information for the diagnsotics - year, model, engine, mileage, options, aftermarket or factory accessories for your ride. when the issue is happening, what precipitates it, can you predict it and if you can, based on what factors, what kind of work had been done on the car, how old the battery and has the current battery been discharged dead in its known life...

without any of that information, you will not get much help, as it is hard to just hear "my ABS light is on", and answer, "oh, it is because you have rear window open"... i wish it were that easy... lol....

2003
E53 3.0
172K
Stock everything except sub and amp which was done 3 years ago.
Battery I replaced about 4-5 years ago

check the charging voltage, and battery voltage under the load, to make sure that your battery is not dying - when batteries die, they "give" out vibes that show up as strange things in the car... search the forum, there were very good posts on the battery... once the battery is cleared of the suspicions, then you can move onto the next things...

Mine has been doing this. Given that occasionally the nav does not start and my wife said the radio once failed to connect I suspect it is the plug next to the dsp amp which connects the NAV harness to the rest of the car.

Cant prove it yet and I don't remember if the ABS module lives under spare wheel but I am going to try some contact spray there soon. Mine lit up this morning as soon as I hit the airco button. (It was cool enough when I left the house to go w/o AC but I switched it on around 9 am when the sun got hotter and bingo)

ABS module lives under the hood, in your E53 probably under the oil filter, behind the left headlight... do a google image search for bosch 5.7 (not sure if yours is 5.7 or the other model) but you will see the picture of the module, so you can find it under the hood... not sure about your E70 though...

might need to get that ABS module rebuilt, bosch 5.7's are located right behind/below the drivers headlight in the E53, and with time/mileage and thermal cycling the power contacts start to go and they throw all sorts of weird errors. If it's lights that pop on intermittently with hotter weather that is a pretty good cause for needing repair.

Good thing is that there are many competent rebuilders who will do your bosch 5.7 for 90-150 bucks, which is the better alternative in my opinion to getting a remanufactured module from BMW, which will have to be coded after the fact, and costs about 500 bucks to start.

RB is right, if the main culprit is the ABS module, it makes sense to repair it with lifetime warranty, as opposed to buy a new one with 2 year warranty from a dealer... but before getting that deep, lets take baby steps... we haven't heard yet if the battery and alt have been ruled out...