[NickD]

Each wheel bearing has a speed sensor built into it.
The sensor is a electromagnet and it is stationary.
On the hub side of the bearing, there is a ring with, what a novice would call, teeth.....like a gear.
The two components are the speed sensor.
The electromagnet is powered whenever the vehicle is running and, when in motion, the trigger wheel (gear) turns with the vehicle wheel.....as each 'tooth' passes the electromagnet, a return signal variation, due to the proximity of each tooth passing the magnet, is sent the the ABS computer.
As long as wheel speeds are the same, plus or minus a pre-established range, the computer is satisfied that it is sending a signal and recieving a signal.

All that gobblygook to say that the metallic brake dust is attracted to the electromagnet.......and sometimes too much of it accumulates.
This interferes with the signal and is what sets the ABS/TRACTION CONTROL lamp.....the computer is getting flawed information.

All vehicles have the potental for this concern, but as a percentage, few are ever affected by it.
Usually any accumulated metallic particles drop off when the ignition is turned off.....but, as can be seen, sometimes a bit hangs in there.

Really nothing the consumer can do to avoid it.

Usually, simple cleaning and compressed air blow-off of the electro magnet (known as a stator btw) resolves the issue.

Rob

Are you saying the reluctors and the Cruze are not shielded? Weird, are shield on any other ABS vehicle I have worked on. Also paranoid with insurance companies, if involved with an accident, even though your car was parked, will claim its your fault because your ABS lamp stays on.

While that Stanford professor says having ABS is 14% safer thus becoming mandatory by congress, read that at the other 86% of the time, they are worthless.

But at least the Cruze has a separate ABS sensor, essentially just a coil of wire wrapped around a permanent bar magnet. Others use a Hall Effect sensor, more expensive, but degrade with temperature.

Some had this sensor integrated with the hub assembly, so have to replace the entire $$$$$ assembly just because of a broken wire inside of that coil.


ABS has two test modes, if the ABS light comes on with the ignition and stays on, it did not pass the static test. ABS master relay, pump relay, pump, and all four sensors are tested for open or shorts. If any fail, that light will stay on. But can come on at about 5-8 mph for the dynamic test, hear that buzz, then tests all the sensors for pulse output, this is where a plugged reluctor can be the culprit.

Since the traction control depends on the same wheel sensors, and if faulty, that lamp should come on as well.

That connector you see on that photo above can also be the culprit, done only for assembly convenience, since these pulses are applied to a very high impedance CMOS transistor, the slightest bit of corrosion can kill the signal. Ran across these as well, just cut them out and solder and water proof them. Its not like I am changing the sensor several time per day and need that connector for convenience. How many times does convenience cause a lot of extra grief? Don't need any more grief.

 

[NickD]

Nick,

Read my post above yours.

Rob

Cruze is still using the separate sensor for around 15 bucks, so do not quite get why the hub/bearing assembly has to be replaces, unless that shield is rusted out.

Not really much of a hub/bearing fan, another limited lubricated bearing, doesn't have to be mileage that wears them out, just time, that grease gets rock hard. and even worse when they are made in China.

Not a darn reason in the world the old fashion Made in the USA Timken adjustable bearings can't be use, even in a FWD vehicle. When doing a brake job, can be cleaned, would be out 80 cents for a new seal, and repacked with new fresh grease. Never ever had a bearing failure with these, but they claim people didn't know how to properly adjust them, so now hub bearings!

On some vehicles, 300 bucks each, and if all four fail, 1,200 bucks plus tax, and just for parts. Miserable to replace, because well rusted in. In my experience, another way overpriced throwaway part, even further complicated by integrating the ABS wheel sensor in these things.

Guess they call this progress, I call it screwing the consumer.

 

[NickD]

I loved the 3-4 transistor HEI distributors and 10SI solid state alternators where we even borrowed NASA thick film technology for superior reliability. And far superior to contact points. Even installed these in my pre-1972 GM vehicles.

But with OBD I and literally hundreds of thousands of transistors to get that same spark, started carrying towing insurance.

 

[NickD]

Typical generic scanners do not show ABS codes, for years, required a GM Tech I or II scanner with an ABS module. Something about liability that doesn't make a bit of sense. In theory at least, ABS is an auxiliary add on system that is not suppose to inhibit normal braking. But anyone can work on their own primary braking system, but not on the ABS.

I said in theory, because if you run across a modulator with a valve stuck closed, that particular wheel will get no braking whatsoever. And if the valve driver transistors are turned on by a 5 volt microcontroller that sees a transient that shorts out the outputs to Vss, all four transistors will be turned on, all four valves will be enegized, no brake fluid passage period, and you will have no brakes at all. Can also be caused by corrupted firmware.

ABS operates by interfering with the flow of brake fluid to each wheel! But it is the law.

Polarity does make a difference, positive spike is greater than the negative one. Shop manuals are written in such a way, where they say, solid state, do not test. Never read anything so idiotic in my life, you need the proper test equipment to check these out, and an ohmmeter is the worst possible tool to do this with. Should show the waveforms.

Can tell you as a long time engineer, designing any component is easy, the real difficult part is how to test it. To make sure its reliable and meets all specifications. Connectors are only used for assembly convenience, been saying this for years, best connector is NO connector. But outruled by production cost.

Diagnostics are also short of a bad joke, no secondary references, only detects an open or a short, but not if a component is way out of tolerance. Cure for this is to replace with a known good component. But how does one know its a good component if zero specifications are given?

Was talk about hiring hundreds of thousands of skilled electronic technicians when OBD I first came out. Never happened, some guy good at changing mufflers is handling this chore. And you wonder why we have problems.

 

[NickD]

We were all darn near 20 years longer the last time we could reset the codes in the vehicles made at that time by disconnecting the negative lead of the battery.

But didn't even need to do that, just needed a paper clip wire to short out a couple of terminals on the diagnostic connector. Could call this the good ole days, today you need a way overpriced scanner to do this. But with most ABS, after the problem is cured, will reset itself.