This started happening this weekend. It happens about once every other day I drive the car now. What happens is I'm just driving normally, usually in a stright line or a gental turn, and the traction control light starts flashing and it kills power to th car. I cannot accelerate and I start slowing down. I have discovered that clutching in solves the problem. But what is the problem exactly? How can this be fixed? Thanks.

Your dealer will have to fix this - hopefully you're still under warrantee.

Have there been any change in tire sizes, pressures, wheels to the car? Possibly maybe there is some suspension piece that is out of wack?

I have experienced the power cut...

I had to pull over and turn off the ignition, then restart and it has been fine since then.

but it does kill power and you cannot do anything but roll to safety or pop start it while it is still rolling.

Hope mine doesn't start acting up again.

Kev, I got new tires put on last week, and I just painted my wheels so they were all off the car just before this started happening.

Kev, I got new tires put on last week, and I just painted my wheels so they were all off the car just before this started happening.

That's the likely culprit there. All 4 corners or just 1 axle?

Just one axle. I had the rears replaced then rotated to the front. I now have 2 dunlap F901 225/45/17 in the front and 2 AVS ES100 235/40/17 in the rear. All four of them are between 50-70%

How can that cause this problem? Again, it only happens about once every other day, and I've noticed that it happens in sweeping bends under power. I clutch in or turn the car off and it stops doing it.

The DTC has to be noticing different movement of the 4 wheels, thinking you're constantly slipping since the different tires aren't moving the same. Just my opinion.

Lots of threads recently on this and other Z boards with users having squirrelly handling; and the one common theme has been running mismatched tires.

Are those the OE tire sizes? Calculate the rotational diameter of the front/rear tires and see how close they are to OE specs. I had a problem very similar to what you are experiencing when I when I bought new tires for my M3 initially. I was running 225/40/19 front and 275/30/19 rear. The traction control nearly put me into the wall due to the rotational tire difference.

It's is not just the rotational diameter of the tires on one axle, but the relational rotational diameter of the front to rear which causes people the biggest problem.

Lots of math in here...
http://forums.bimmerforums.com/forum/showthread.php?t=221794&highlight=diameter

Just one axle. I had the rears replaced then rotated to the front. I now have 2 dunlap F901 225/45/17 in the front and 2 AVS ES100 235/40/17 in the rear. All four of them are between 50-70%

How can that cause this problem? Again, it only happens about once every other day, and I've noticed that it happens in sweeping bends under power. I clutch in or turn the car off and it stops doing it.


Were the tires the same sizes all around before this?

It's is not just the rotational diameter of the tires on one axle, but the relational rotational diameter of the front to rear which causes people the biggest problem.

Bingo. I think.

Were the tires the same sizes all around before this?

No. On the car so far I have run these set ups without any issue:

OEM Bridgestone RE0-50 runfalsts 225/45/17

Yoko ES100 235/40/17 in front 245/35/17 in rear

ES100 235s in front, AVS sport 245/35/17 in rear

currently: ES100 235s in rear, with the Dunlap FM901s in the OEM sizing of 225/45/17 in the front. This is my first time running the Dunalp, but as you can see, I have run an assortment of tires and sizes in the past without issues. I can see how mismatched tires can be an issue, but this is the first time I have seen it. All the tires are in good condition, and I'm not noticing any loss of traction, even during the problem with traction control.

I honestly thing it is a tire size problem from the description... sometimes with new tires there is the first couple hundred of miles where they are 'sloppy'.

From doing some math... it looks like the 235/40/17 rears are telling your car that the rears are travelling 2.3% faster than the fronts. I unfortunately don't know what the allowable tire slip is for the Z4, but I would think that probably is part of it.

If you had 245/40/17, the diameter would be the same as the 225/45/17.

So I should see if it clears up from the tires breaking in, if not, look at matching the sizes.

Thanks for your help guys.

Does it happen all the time? I had some sort of sensor go bad on one of my e46's rear wheels. It was intermittent but it would set off the traction control at inopportune times.

No, it's on average every other day I drive the car. It has happened 4 times in the past two weeks.

I had two tires replaced before. They said to put the new ones on the rear axle. Try rotate the new tires to the rear axle.

OEM Bridgestone RE0-50 runfalsts 225/45/17

Yoko ES100 235/40/17 in front 245/35/17 in rear

ES100 235s in front, AVS sport 245/35/17 in rear

I had two tires replaced before. They said to put the new ones on the rear axle. Try rotate the new tires to the rear axle.

He has different size tires on the front so rotating front to rear is not good.

hey did you get this problem to stop cause i have the same problem sometimes. The traction control light comes on, the car holds the revs back and either you have to turn on the traction control or slow down.