2004 Oldsmobile Alero



January, 29, 2013 AT 1:01 AM

The other day my Anti-Lock warning light and Service Vehicle Soon light came on and my brakes started acting funny. I drove it like that for a couple days. The lights would come on randomly after driving a few minutes then stay on until the car was shut off. I then replaced the wheel bearing and now the lights stay on from the time the car is started until you shut it off.

1) I DID double check the plug in that goes to the sensor.
2) Why would this replacement make the lights stay on constantly now?
3) I am desperate for help. This is an $88 item, I can't afford to keep buying them.


3 Answers



January, 29, 2013 AT 1:13 AM

What led you to the wheel bearings? GM does have a real big problem with them but there should be a diagnostic fault code stored in the computer. That will direct you to the circuit or system that needs further diagnosis. Once the yellow ABS warning light completes its self test in a few seconds, if it stays on right after that without moving the car, it's not wheel bearing-related. The wheel speed sensors don't develop a very strong signal to begin with and when the bearings develop a little normal play, (in as little as 15,000 miles), the signal can drop so low the computer can't read it. It will set the appropriate code and turn on the warning light, but the car has to be moving for that lack of signal to be detected. If the light turns on right away while standing still, that is due to an electrical problem with a sensor, or some entirely different problem. The fault code will provide more details.



January, 29, 2013 AT 1:28 AM

I am very limited on money. The reason I started with the wheel bearing (speed sensor) is because that is what the guy at O'Rileys told me it most likely was. Don't you think it is strange that the warning lights would come on after driving for a few minutes before the replacement and now that it is replaced it is on from the second you start the car?

How do I get this diagnostic fault code that is stored in the computer? And is that expensive?



January, 29, 2013 AT 2:57 AM

First of all, you took the advice of someone whose job it is to sell parts. Most of the time they never were mechanics and have little or no experience working on cars. They are trained to look up parts. The person most likely based his recommendation on what he sells the most of, and for GM vehicles that is wheel bearings. GM likes to use large assemblies made up of many smaller parts because the cars go together faster and cheaper on the assembly line. Owners pay for that later when they have to buy those more expensive assemblies. In this case, you bought a wheel bearing to get the wheel speed sensor. And I might point out, you got a deal. These bearings used to cost around $250.00.

Second, you said the brakes acted "funny". That doesn't tell us anything. If you can provide details and observations, the exact symptoms can be helpful in steering you in the right direction.

Third, did you just replace one bearing assembly, and if so, how did you decide which side to replace? The next point is related to this.

Fourth, you have the worst car brand in the world when it comes to making mechanics frustrated, and now you are going through exactly what we do. You said you drove it for a couple of days with the problem. That should not really be long enough to cause the frustration but here's a copy of what often happens when people wait weeks or months to have the problem diagnosed and repaired: The problem is when you wait a long time to have it repaired, you're going to be surprised with additional parts that no one was expecting. To set the diagnostic fault code, there is always a long list of conditions that must be met, and one of them is that certain other codes can't already be in memory. In this case, the computer looks at all four wheel speeds and compares them to be sure they're equal. Once a code is set for one wheel, the computer won't be able to use it as a reference to test the other wheels. In the meantime, with the extremely high failure rate of these bearings, it is likely a second one will develop signal dropouts but no fault code will be set. When you finally take it in for repair, there could be two wheel bearings that need to be replaced but there will be only one fault code in memory. The mechanic will only know about that one, and that's what they base their repair estimate on.

Once the first bearing is replaced and the fault code is erased, the computer can start doing self-tests again, and the new code shows up on the test drive. The mechanic is frustrated because he has to start all over with the diagnosis, and he has to tell you the car is not totally fixed yet after you spent all that money. You're frustrated because you're sure he didn't diagnose it properly the first time. Most of that frustration can be avoided if you have the first problem repaired right away.

Okay, I'm back. First of all I should point out that when I referred to the really high failure rate of the bearings, they aren't really failing. They develop a little play which is perfectly normal on any car that uses this type of bearing. The failure rate refers to a failure within the system. GM's style of wheel speed sensor doesn't develop much of a signal to start with. The little play that develops, often in as little as 15,000 miles, causes the signal to drop even lower; often low enough that the computer can't read it. It sets the code and turns on the warning light when it sees three wheels turning and not the fourth one due to the lack of a signal. The immediate fix is to replace the bearing. The long-term fix is to use the same type of sensors everyone else uses, but GM seems to prefer selling lots of replacement parts. That correlates with most of their other business practices.

The same bearing is used on cars without anti-lock brakes, just without the wheel speed sensor. The old bearing you took off can be used on one of those cars with no modifications or problems. In fact, it is real common to find these bearings WITH the wheel speed sensor cost a lot less than the same one without the speed sensor. We always check the prices for both when we need a bearing for a GM car without ABS. We can save the customer money by doing that.

To read the diagnostic fault codes you need a scanner that can access the Anti-Lock Brake Computer. The inexpensive code readers used by most auto parts stores typically only access the Engine Computer. The dealer will be able to read the codes for you but GM dealers charge quite a bit. Almost all independent repair shops have aftermarket equipment that will do most of what the dealer's equipment will do. The scanners are very expensive and it costs them a lot to keep on updating them every year, so they have to charge for reading the codes to help pay those costs. A typical charge might be around $50.00, but I'm guessing. I have my own Chrysler scanners to work on my own cars so I don't know what the going rate is now.

You have to understand too that fault codes will never say to replace parts. They only indicate the circuit or system that needs further diagnosis. They are just a starting point in the troubleshooting process. While it's true the sensor or solenoid referenced in the code will be defective about half of the time, it is just as likely you'll find a stretched terminal in a connector, a corroded terminal, a cut wire, or a computer problem. Too many people think we just read a code and it tells us which part to replace. It's not that easy.

It is also critical to use a click-type torque wrench on the axle nut when you replace the bearing assembly. If the car's weight is ever set down on the bearing while that nut is loose, the bearing will become noisy and sound like an airplane engine. Some people put the tire on and lower the car, then let that tire hold the axle from spinning when they tighten the nut. When that makes the bearing noisy, they blame it on the cheap part. Even when you don't do that, if the nut is not tight enough, the bearing can wobble a little internally, and that can lead to wheel speed sensor signal dropouts. Most front-wheel-drive cars call for around 180 foot pounds of torque on those axle nuts, and that's quite a bit. A lot of GM axle nuts call for as much as 240 foot pounds.

Many of those nuts are "torque-to-yield" nuts which means they are only to be used once. If you loosen them, you must replace them because they will not hold proper tension after that and they can work loose. Higher-quality bearings will come with a new nut when they are needed.

So, the place for you to start is by having the code(s) read. Your old bearing might have been causing a problem and needed to be replaced, but for sure, paying to have the codes read is less expensive than throwing random parts at the problem.

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