If you’re experiencing the classic dashboard lit up like a Christmas tree scenario in your E90 3-series BMW, you are probably thinking that something horribly catastrophic just happened to your car.

But don’t worry, yet.

Recently my 2007 335i broke down on the highway on the way home from my mother-in-law’s birthday celebration. I was with my wife and daughter and it was just getting dark out. It was also the hottest and most humid day of the year so far with temps around 90 degrees.

This was the worst possible time to experience a break down!

The car was cruising along for 15 minutes on the journey home, without any hint of a problem. All of a sudden, every warning light in the car came on and it began slowing down. The speedometer dropped to zero, even though we were going 65 MPH. The transmission shifting felt clunky, too.

The coolant, ABS, airbag, DSC dynamic stability control, brake, service engine soon, yellow gear of death, and others, came on and cycled through like a holiday light display. The car was jerky and then would not drive. Once I pulled over to a safe place, I turned the car off and back on. I tried to drive, but the shifter would not come out of park. I thought the car was in limp mode, but it really wasn’t.

Looking back on all of this now, it’s easy to see that this group of symptoms was a classic voltage regulator failure. When that part fails, the alternator overcharges the system with 18+ volts, when it should only be receiving in the 13.8 range.

As a result, all of the car’s complex modules and computer systems go haywire due to the extra voltage; if you continue limping the car along like this, a module or electronic part may get fried. So it is best to pull over and call for a tow.

Thankfully, I had AAA roadside service, which I highly recommend to anyone. I have the gold service for around $120 per year, which includes up to 100 miles of towing. That’s the one to get.

My mother in-law came to pick up my wife and daughter to take them home, and I waited with the car for AAA who arrived 15 minutes later. I can’t say enough good things about the AAA service. When you need it, you need it. Especially if you own several BMW cars.

I had to car towed to my house, though I was tempted to bring it to a local shop because I was so thrown off by the number of lights and codes. Upon scanning the car with my $60 C310 scan tool, I saw many codes for over-voltage. That is a clear sign that the voltage regulator needs inspection.

I ordered a Bosch unit from FCP Euro for around $43 and had it the same day. Typically, there is no need to replace the entire alternator, which is more like $400 and a ton of work. To replace the entire alternator, the oil filter housing must be removed in order to make room. I recommend trying the $43 part first, which can be installed in less than an hour with simple hand tools.

Upon removing the old voltage regulator, I saw that the brushes were very worn down. You can see in the image above that the new brushes are more than twice the length of the old ones. These brushes wear down over the years and eventually fail; the alternator is designed that way and the regulator is designed to be easily removed and replaced.

The BMW part number for this regulator is 12317561939.

If you drive an E90 3-series, replace these brushes as soon as possible. It’s an easy job, less than $50 and just might save you from an unexpected break down.

Buy a new regulator here to avoid a future headache!