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Old 10-02-2012, 07:05 PM   #1
Caden
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Tires replaced at discount tire, now dsc and yellow brake light are on.

Just replaced my two front tires and balanced the back two. Right after I left discount tire I realized my DSC Light and the yellow brake light were on. What could be causing this? Could they have broke something?

SES light not on or any other lights.

Last edited by Caden; 10-02-2012 at 08:06 PM.
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Old 10-02-2012, 07:09 PM   #2
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If the DSC control unit senses a 2% (or is it 2mph?--i forget) difference in rotation speed between the two axles, the DSC light could illimunate. Yours must be so extreme that the system has disabled itself. how big of a difference in tire wear? same tire type AND size? more info please
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Old 10-02-2012, 07:16 PM   #3
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Different tires. Same specs. 225-40-zr18. Back tires are 245-40zr18
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Old 10-02-2012, 07:56 PM   #4
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They messed something up. Bring it back.
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Old 10-02-2012, 07:59 PM   #5
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Should you have 245/35 rears?
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Old 10-02-2012, 08:05 PM   #6
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Should you have 245/35 rears?
I did have 250/35 in the rear but the tire was due for replacement and the local shop down the road only had 245/40. These lights haven't come on the whole time i've had this tire set up, until discount tire touched the car.

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Old 10-02-2012, 08:03 PM   #7
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I brought it back, manager says he has no clue and I think he doesn't think that they caused it. I was like wtf. The DSC is not working, I shouldn't be driving the car, right? What should I do next? I have to go back tomorrow and speak with the store manager I guess.

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Old 10-02-2012, 08:19 PM   #8
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I brought it back, manager says he has no clue and I think he doesn't think that they caused it. I was like wtf. The DSC is not working, I shouldn't be driving the car, right? What should I do next? I have to go back tomorrow and speak with the store manager I guess.
Drive it all you want, lots of cars with RWD don't have DSC so your car with the DSC disabled is no different than these other cars.

They managed to knock a sensor off. You need to take the tires off and inspect all four corners for the speed sensors to be intact.
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Old 10-02-2012, 08:22 PM   #9
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Your trouble is in the Brake Light, not the speed sensors. It never hurts to take the tires off and look, but the brake light means that the car thinks the brake fluid is low for some reason. Open the hood and look at the brake fluid reservior.
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Old 10-02-2012, 09:04 PM   #10
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Originally Posted by Caden View Post
I brought it back, manager says he has no clue and I think he doesn't think that they caused it. I was like wtf. The DSC is not working, I shouldn't be driving the car, right? What should I do next? I have to go back tomorrow and speak with the store manager I guess.
You will be perfectly fine driving it.



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Old 10-02-2012, 08:13 PM   #11
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Have you checked to see if they knocked out the brake sensor?
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Old 10-02-2012, 08:22 PM   #12
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The brake sensor was disconnected. This would trigger the DSC light, right? They knocked it out when they were balancing the back two tires. If this is the case, how long would it usually take to reset?
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Old 10-03-2012, 01:59 PM   #13
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The brake sensor was disconnected. This would trigger the DSC light, right? They knocked it out when they were balancing the back two tires. If this is the case, how long would it usually take to reset?
The left front and right rear have two sensors, one monitors wheel speed the other monitors brake wear.

In the days of old, people had to -- wait for it -- _look_ at the brakes to see if they were worn out or not. BMW put in a sensor that "looks" for you constantly so you do not need to do an inspection. The Brake Wear warning comes from one of two things, the brakes are worn or the sensor is broken/disconnected. The brake wear will not trigger a DSC light.

The wheel speeds are monitored to prevent brake lock up or uncontrolled wheel spin. If you slam on the brake and lock a tire, the ABS jumps into action to release the brake pressure to that tire so it can turn -- the idea is that a tire that is turning can be aimed in a new direction while a tire that is skidding will continue on its path regardless of where you attempt to get it to go -- and if the car detects wheel spin, then it will apply the brake to that wheel and reduce the application of throttle.

Since there is a brake wear sensor and a wheel speed sensor both at the right rear corner, I suggest taking that tire off and inspecting the wires to these sensors, and inspecting the brakes at the same time. It is possible that the brakes just happened to wear out at the same time as the tire service, and it is also possible (probable) that the tire service disturbed the sensors.

In any case, the best course of action is to go back to the tire store and take all four tires off and look at the brakes and check the condition of the wires that lead to the wheels. The second best course of action is to blow the tire store off and do this at home.
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Old 10-02-2012, 08:28 PM   #14
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Yes, it would trigger the traction control fault. The car sees the rear tires going too fast relative to the front tires, the brakes are applied and the throttle is reduced. If the brakes are disabled, then they cannot be applied and the light comes on to tell you the system is unreliable/disabled.

The light should go out if you set the ignition to Position 1 for 30-ish seconds so the car can look to see that the systems are all System Go.
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Old 10-02-2012, 08:53 PM   #15
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Yes, it would trigger the traction control fault. The car sees the rear tires going too fast relative to the front tires, the brakes are applied and the throttle is reduced. If the brakes are disabled, then they cannot be applied and the light comes on to tell you the system is unreliable/disabled.

The light should go out if you set the ignition to Position 1 for 30-ish seconds so the car can look to see that the systems are all System Go.
I set in position 1 for approx 2 mins. No change. The tire size hasn't been a problem for like 6 months. Why would it be now?
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Old 10-02-2012, 08:59 PM   #16
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I set in position 1 for approx 2 mins. No change. The tire size hasn't been a problem for like 6 months. Why would it be now?
Honestly, it isn't. The person who mentioned it is incorrect. You would run into mechanical and maybe electrical issues if you were running 16" wheels/tires in the front and 18" tires/wheels in the back(in simple terms). The problem is a speed sensor that is now dirty or has become dislodged.This has happened to a few members in the past. The brake sensor, unless it's the ABS sensor, has nothing to do with anything other than how much life you have left in your pads.

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Old 10-02-2012, 08:43 PM   #17
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The correct tire size for the back is 255/35/18. Currently, there is discrepancy in what the sensors are measuring up front and in the back, which is probably why your DSC light is on. It is also possible that you will need a alignment along with correct size tires.

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Old 10-02-2012, 08:46 PM   #18
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The correct tire size for the back is 255/35/18. Currently, there is discrepancy in what the sensors are measuring up front and in the back, which is probably why your DSC light is on. It is also possible that you will need a alignment along with correct size tires.

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I'm having a hard time believing this. 325i's come stock with like 195/50/16
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Old 10-02-2012, 09:14 PM   #19
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I'm having a hard time believing this. 325i's come stock with like 195/50/16
Stock tire size for a 325 is 205/55/16, which results in an overall diameter of 24.87'', not too different than that of a 225/45/17, or 205/50/17, or 225/40/18, or 255/35/18 (all stock sizes).

The correct tire size combination for a staggered 18 inch set up is 225/40/18 fronts and 255/35/18 rears (for example, stock ZHP). The overall diameters are 25.08'', and 25.02'' inches respectively, the slight difference is negligible.

OP's problem is having incompatible tire sizes in the front and rear. He could have gone with 245/40/18's all around (even though not a stock size), or 225/40/18 all around (assuming wheel width allows). Putting one size in the front and the other in the rear is a NO GO.

Let me elaborate even further:

If you install 225/40/18 in the front and 245/40/18 in the rear, rear tires will be rotating 809 times per mile, while the fronts will be rotating 829.3 per mile, the difference is quite possibly large enough to be picked up by the DSC sensors. For the correct rear tire size, i.e. 255/35/18, revs per mile is 831.3, which is much closer to that of a 225/40/18 size tire, and the difference is within DSC's operating limits.
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Old 10-03-2012, 02:24 AM   #20
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Stock tire size for a 325 is 205/55/16, which results in an overall diameter of 24.87'', not too different than that of a 225/45/17, or 205/50/17, or 225/40/18, or 255/35/18 (all stock sizes).

The correct tire size combination for a staggered 18 inch set up is 225/40/18 fronts and 255/35/18 rears (for example, stock ZHP). The overall diameters are 25.08'', and 25.02'' inches respectively, the slight difference is negligible.

OP's problem is having incompatible tire sizes in the front and rear. He could have gone with 245/40/18's all around (even though not a stock size), or 225/40/18 all around (assuming wheel width allows). Putting one size in the front and the other in the rear is a NO GO.

Let me elaborate even further:

If you install 225/40/18 in the front and 245/40/18 in the rear, rear tires will be rotating 809 times per mile, while the fronts will be rotating 829.3 per mile, the difference is quite possibly large enough to be picked up by the DSC sensors. For the correct rear tire size, i.e. 255/35/18, revs per mile is 831.3, which is much closer to that of a 225/40/18 size tire, and the difference is within DSC's operating limits.
Nail on the head. The DSC, TCS and ABS all work by monitoring the wheel speeds relative to each other. When one wheel starts spinning faster than the others, it indicates that wheel is slipping and the DSC/TCS/ABS will intervene to try and stop it from slipping. Here, your tire sizes are such that your front wheels are ALWAYS spinning faster than the rears (since the rears have a larger diameter) and the DSC is basically telling you to go **** yourself since it has no idea what's going on or how to fix it. You can drive fine without it, but I would just keep the car happy and install the correct diameter tires.

Also, your ABS is likely inop since it works off the same principle as the other systems. You may get by just fine without it, but if you are not a skilled threshold braker I wouldn't chance it (especially in rainy climates).

Honestly I would expect a service manager to know all of this since it is very important with modern cars. I think it could be considered unsafe of him and you may want to speak to someone higher up about it and let them know about the whole situation.

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