Why do e90s eat wheel speed sensors?

[RealBACONATOR2]

Hi all, I'm at 50,000 miles and it seems like I'm just replacing wheel speed sensors all the time. What gives? Is this just a part that's especially fragile, or what? And how much do you normally get charged by mechanics to replace it? (I don't own a jack, live in small apartment)

[nicholg2286]

I've had 3 vehicles in the E9x series with over 250,000 miles between them all. Never had to replace one. Maybe it's a hub issue?


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[fumigator]

130kmiles on my 07 335i and no need to replace. I have the brake light trifecta due to the pump brushes.

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[JDStrickland]

Hi all, I'm at 50,000 miles and it seems like I'm just replacing wheel speed sensors all the time. What gives? Is this just a part that's especially fragile, or what? And how much do you normally get charged by mechanics to replace it? (I don't own a jack, live in small apartment)

Why are you replacing speed sensors? They are very robust and should never need replacing. A wheel speed sensor shouldn't take more than about 15 minutes for a mechanic to replace, or about an hour for you the first time.

Please explain the symptom set that sends you to the wheel speed sensors.

[RealBACONATOR2]

Sorry, yeah I should have provided more details. On the dash, yellow BRAKE light, yellow brake symbol light, yellow ABS light. In INPA, error code for front right wheel speed sensor.

[JDStrickland]

I assume you are clearing the fault and it returns. It's odd that you are going through them, they are all but lifetime items. They fail, but it's not common. Have you checked the fluid level in the brake reservoir? Usually, the yellow lights are telling you that the fluid needs you. If the fluid gets to a point where the ABS is affected, then that light turns on too, but INPA shouldn't call this out as a speed sensor.

[RealBACONATOR2]

I assume you are clearing the fault and it returns. It's odd that you are going through them, they are all but lifetime items. They fail, but it's not common. Have you checked the fluid level in the brake reservoir? Usually, the yellow lights are telling you that the fluid needs you. If the fluid gets to a point where the ABS is affected, then that light turns on too, but INPA shouldn't call this out as a speed sensor.

Yeah I've just been taking it to my mechanic for a replacement. I think I've gone through three at this point? But I haven't seen if the sensor itself is crushed or something. I should ask the shop if it's always been the front-right.

[JDStrickland]

I'm on BMW #6 at my house, the latest is an E93, but in all of the others I have never replaced a speed sensor. My neighbor needed a speed sensor once, but he used a jack to raise the car by the lower control arm, and pinched the wires to the speed sensor in the process.

Do you know how a speed sensor works? I will explain....

There is a ring that looks sorta like the main sprocket on a bicycle chain, except the teeth are square instead of pointed. At one location, two of the teeth are filled in, this makes a reference point. The sensor is located nearby to the sprocket and is essentially a magnet, as the teeth of the sprocket go by the magnetic field collapses and produces a square wave, and the point where the two teeth are filled in makes a longer pulse that is the reference. The computer counts the pulses and the reference should be every 60th (I made that number up) pulse so that the car knows that the tires are all rotating at the same speed, and it then activates ABS or DSC as needed to keep the car going straight. If the brake fluid is low, then ABS will go offline, and this will also take the DSC out because these are essentially the same thing, but one is when the car is stopping and the other is when the car is going. There isn't much that can happen to the sensor itself, but the wires can be compromised is they are routed improperly. Make the car safe and turn the steering wheel from lock to lock and see if the wires are being stretched.

[Critter7r]

Sorry, yeah I should have provided more details. On the dash, yellow BRAKE light, yellow brake symbol light, yellow ABS light. In INPA, error code for front right wheel speed sensor.

That sounds like it could be a battery issue.

[RealBACONATOR2]

Ok so the mystery continues, I had the rear left wheel speed sensor diagnosed as defective at a BMW dealership in 2015 and replaced, front left wheel speed sensor diagnosed and replaced in 2018, and now INPA says it's the front right sensor.

So uh, not sure exactly what that means. Maybe they were all improperly installed at the factory and the wires have gotten pulled? I'll break out a jack and phyically inspect the newest faulty sensor to see if it's actually broken.

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That sounds like it could be a battery issue.

How would I determine if it was a battery issue or the sensor actually being broken?

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I'm on BMW #6 at my house, the latest is an E93, but in all of the others I have never replaced a speed sensor. My neighbor needed a speed sensor once, but he used a jack to raise the car by the lower control arm, and pinched the wires to the speed sensor in the process.

Do you know how a speed sensor works? I will explain....

There is a ring that looks sorta like the main sprocket on a bicycle chain, except the teeth are square instead of pointed. At one location, two of the teeth are filled in, this makes a reference point. The sensor is located nearby to the sprocket and is essentially a magnet, as the teeth of the sprocket go by the magnetic field collapses and produces a square wave, and the point where the two teeth are filled in makes a longer pulse that is the reference. The computer counts the pulses and the reference should be every 60th (I made that number up) pulse so that the car knows that the tires are all rotating at the same speed, and it then activates ABS or DSC as needed to keep the car going straight. If the brake fluid is low, then ABS will go offline, and this will also take the DSC out because these are essentially the same thing, but one is when the car is stopping and the other is when the car is going. There isn't much that can happen to the sensor itself, but the wires can be compromised is they are routed improperly. Make the car safe and turn the steering wheel from lock to lock and see if the wires are being stretched.

That's how I understood them to work as well, and I've seen youtube videos of how the wires are run around the whole wheel area. Based on those, I guessed it was possible that road debris could have damaged the sensor or wiring, since it does kinda hang down into the wheel well area. I'll do that check you mentioned and see what I can see. Weird to know that this doesn't happen to all e90s.