A couple of weeks ago as I was out driving, the Automatic Stability Control (ASC) on my BMW 528i randomly kicked in and started cutting power to the engine. I pushed the ASC button a few times, but it didn’t do anything, and when I pulled over and stopped, the engine stalled. After letting it sit for a few minutes, I started it again, and the light remained off and the car drove fine. However, just a few miles down the road, the fault emerged again. In my case, this was not proving to be fun.
Still a good 20 miles from home, I pulled over again and checked the fuses, which were both fine. I disconnected the battery and let it sit for five minutes, and then reconnected it. Once again, the fault disappeared, and this time I drove for about twenty minutes before it came on again. The final time it came on was just two miles from home, and I managed to drive it home without it stalling again.
Research the forums, no one seemed to have the exact same problem I did. In all other cases, the check engine light had come on as well, and most were able to narrow it down to a either a problem with the ABS system or a faulty wheel speed sensor. One person had a similar problem with the traction control actuator, but on a 1998 model with the M52 engine, which uses a separate actuator with a cable. Mine, however, is an M52TU engine (which came out in 1999), and controls the cruise control and traction control electronically.
In the end, I decided to buy an OBD-II scanner to see if that could throw light on the situation. I purchased the Creator C110 BMW Code Reader, as it has very good reviews and reads BMW-specific codes. It pulled a number of codes (more than I expected, actually), including a faulty mass air flow sensor and a mechanical throttle issue.
With that information in hand, I pulled the air intake system apart, installed a new MAF sensor, and thoroughly cleaned and lubricated the throttle body and cable (located under the intake manifold in the photo below). I then reset the codes.
Since then, the problem has not returned, and the car seems to be driving more smoothly. I’ve activated the traction control by launching on slippery surfaces and everything seems to be working as it should. I can only assume that a combination of that sticky throttle and an electrical gremlin of some sort caused the problem. I’ll report back if anything happens again.
(NB: Another code that showed up tells me the thermostat is stuck open, hence the problem with the O2 sensors you see on the screen of the code reader above. Replacing the thermostat is a job for this week.)