How To Install a Transmission Cooler on a Grand Prix GXP

Diagnosing and Replacing Front Wheel Hubs Bearings or Speed Sensors on Grand Prix GXP

This is a really common issue on Grand Prix GXPs and it gets confused with a similar issue I'll briefly mention

If your Drivers Information Center (DIC) says

Service Brake System... Service ABS System... Service Traction System... Service Stability System... Service Variable Effort Steering... and then repeats, your EBCM has gone bad (also known as the ABS module). You can either pay a dealership to replace it for you, for the mighty sum of $1200+ like I did, or, remove it yourself and mail it to a place like Module Master to get repaired for under $200. Wish I knew that Module Master existed before I spent $1200+... Your parking brake symbol will also likely be lit up, despite the parking brake not being on, but that symbol is in the gauges, not on the DIC.

If your DIC says

Service ABS System... Service Traction System... Service Stability System... and then repeats, it can be one of your hubs... the bearings... the wheel speed sensor... or the wire that goes to the brakes. That is what this short page on my website is going to be about.

My main focus is on hub replacement as the solution, but the PDF I've created should help with all possible issues. My procedure below that, however, is specifically with regard to front wheel hub replacement.

Disclaimer

If you follow my instructions, you’re doing so at your own risk. By proceeding to follow anything I have written below, you agree to hold me without liability. The guide below is simply how I did it on my GXP.

If you found this guide helpful and would like to make a donation to me for my time and effort writing this guide, providing diagrams, and creating a website for it, you can donate via this PayPal link.

You need to buy a high quality OBDII scan tool, not a cheap one or you'll be throwing money at your car

I see guys throwing parts at their cars trying to DIY fix them, and they aren't even using a scan tool to find out what's causing them to have lights on their dash and DIC. This isn't the 1980s anymore and our old GXPs can tell us quite a bit of data to help us narrow problems down. (It's a shame they can't tell us when they have a torn rubber on the swaybar or a bad tie-rod end, but oh well). DO NOT waste your money on a cheap scan tool. Most cheap code readers/scan tools don't show ABS codes and therefore they aren't all that useful. You need a better one that can read ABS, Airbags, TPMS codes and more since our cars tend to have electronic problems as they are getting older. A Blue Driver is what I have and it's freakin' awesome. You can buy a Blue Driver on Amazon. Use it to scan your car while the code is actively cycling those annoying messages on the DIC and the Blue Driver will tell you exactly which wheel sensor is causing the message to show up and annoy you. If you turn off the car... ABS codes go away with it. So carry your Bluedriver with you in your glove compartment so you can plug it in when the error gets triggered. (Make sure to set up your Bluedriver in advance (connect via Bluetooth to your phone) so you are ready to scan even if you're in a hurry on your way to work. Don't leave it in the box and wait for a problem to occur. Get it paired with your phone when you first receive it.)

Is there any way to know if your hubs are bad without a scan tool?

Honestly, it's pretty obvious if you jack your car up into the air and put the car on jack stands.

Once you've done that, put your hands on the top and bottom of one wheel that's up in the air and see if you can rock the wheel back and forth, top to bottom, very much. If it does move back and forth quite bit, then you should probably replace the hub.

Another way to somewhat tell, is if when you're driving around, and you do a turn at an intersection, if you feel like you hear/feel your wheels grinding like they have gravel in them, that's a good indicator that you should check them. Our Bilstein struts kind of make a similar sound/feeling too though. When driving straight over uneven (imperfect) roads, the car will shake a little tiny bit if your front hubs are worn out. When going over railroad tracks, it'll feel like the wheels are falling off.

I'm not sure how many miles hubs typically last, but I think I got around 50k miles out of my front ones. My part of Texas has a lot of speed bumps, manhole covers, and some damaged roads, so it's not gentle on hubs.

Here's the repair procedure for diagnosing and replacing front hubs on a 2004-2008 Grand Prix or 2005-2008 Grand Prix GXP

Unlike my transmission cooler page, I don't have to walk you through this and spend a billion hours doing so. The service manual (shop manual) for our cars has great information about all of this. I extracted all the relevant pages from my 2005 service manual, then combined them, shuffled them into the order of the procedure, and finally deleted the irrelevant text about how to fix unrelated stuff and I modified the text here and there. There's a little repetitive info, but not too much.

It now reads like an instruction manual and can be navigated one page at a time while you're in your garage working on your car.

The order is:

ABS schematics
ABS connector (end view) diagrams
Testing the resistance of the speed sensors (and similar diagnosis and testing tasks)
Process to remove a front hub with the process to remove the front brake rotors and calipers inserted where it belongs in the order of operations
Process to install new hub, then reinstall brake rotors and calipers, and then finish installing the new hub

Download the PDF

Parts and Tools Needed for Diagnosing Speed Sensors

This is a really annoying process, in my opinion.

First of all, you need a scan tool to get the code to tell you which speed sensor is causing the error messages. I recommend the BlueDriver.
Second, if you're going to follow the shop manual, you're going to need a scan tool that can turn on the fans. I don't have one, so I couldn't do that part of the process...
Related to above... you may have to resort to the tricks discussed in the box below if you don't own a scan tool that can tell the fans to turn on...

If you're diagnosing a speed sensor and your scan tool can't turn on fans...

Here's this post written by supercatxr7 on LS1tech. I'm copy and pasting it here in case LS1tech ever goes down and this text disappears with it:

I've been hunting down a ABS/Traction Control/Stability Control issue on my 2006 GXP. I found the following on another site and it helped me to get to the bottom of my issues and all is good now. My issue was the hub was bad # 1 and also the wiring for the sensor had gone bad along the frame area. Not a grounding/bare wire issue, but I found by hooking up a voltmeter to the wire with ignition on that the voltage jumped around when the wire was bent/shaken slightly for the right front sensor. Clipped the bad area of the wiring harness replaced with new wiring, and all is good.

Anyways - here's the procedure I found on another site and thought it will help others, copied and pasted a few together:

"Each wheel has a AC gernerator that is used to tell the ABS brake module what that wheel is doing. These sensors are nothing more than just a coil of wires with an input & out put lead. Either they work properly, are open( broken wire) or are shorted to ground. Unplug each one & check the tresistance in them. If you have one that is different than the others----- youve found a problem Resistances values need to be 800-1600 ohms.

Once you've confirmed the sensors are all good & the lights are still on, there are other issues. You need to check the wiring from each wheel sensor to the ABS module. Again very easy. Plug all the wheel sensors back in, & then unplug the main plug at the ABS module. Remeber each wheel has it's own set of 2 wires that tell the module what's going on.

With the pin end of the plug facing you you want to check the wiring to each wheel. There are VERY small numbers moulded into the corners of the plug. Looking at the pin end of the plug the numbers start at 1 in the upper right side ending in 11 upper left side. The last row starts with 20 in the lower right & ends at 30 in the lower left.

#2 & #3 pins Right rear wheel

#4 & #5 Right front wheel

#20 & #21 Left Front wheel

#22 & #23 Left rear wheel.

Again check the resistance for each wheel at these pins. They should all be very close to the values you got at the wheel sensors alone. If there is a reading that is out of place, then the problem is in the harness, now you have to find it, but at least you know which area to be looking for."

"I checked the voltage at the end of each harness connector to the wheel speed sensors with the ignition turned on. Three of them were at 4.8 volts, and the RF was varied between 2.1 and 3.6 volts. As I shook the harness next to the RF brake, that voltage at the connector would jump up and down. With the connector still disconnected from the wheel sensor, I probed the length harness with pins and a voltmeter. At the ABS ECM, the RF circuit was 4.8 volts like the other three wheel circuits. As I moved along the harness, it stayed at 4.8 volts until I got to within about a foot of the wheel sensor. Then it dropped off to the lower level I measured at the wheel connector.

I eventually pulled the wires out of the harness guard, and cut open some of the shrink wrap around the wires. Even though the car had not been driven for 5 days, the wires were wet, and the inside of the shrink wrap was full of sand and salt. I think what had happened was that the dirt there eventually degraded the insulation on the wires and was allowing some current leakage that resulted in the voltage drop.

I intended to rewire this part of the harness and replace the end connector. I couldn’t get a new connector at the auto parts stores, but three different stores and a Chevy dealer sold a relatively short section of the harness with a new connector. My conclusion is that this mode of failure must be common, or all of the auto parts stores and GM dealers would not be selling a replacement harness section.

After wiring in the new section on the end of the RF wheel harness, the ABS warning light is no longer coming on."

If all your wheel sensors are good, & all your harnesses are good then you need to be looking at the ABS module itself.

Parts and Tools Needed for Replacing Front Hubs

It isn't difficult, but this whole job is massively benefited by having two people working on the job. I would highly recommend you don't try to do this job solo, unless you have access to a lift and you own all of the specialized tools you might need.

The service manual calls for a J-42129 Spindle/Hub Remover, which from my research, is actually the same one GM recommends using on the rear axle of a Corvette or Cadillac XLR. As long as you have a helper, you don't need one, you just need your thumbs to push on the axle. If you don't have a friend to help you, you probably need one of these hub removers just because you don't have an extra 2 arms to help you. It also calls for a couple specialized die grinder tips for cleaning up the rotors, but they appear to just be wire brushes. We didn't need them, as rust isn't a problem in my part of Texas.

Here's an incomplete parts list (mostly stuff I ordered, with a few other things mentioned that I already own that I know are needed)... consult the PDF to see if you need more... I am going to replace both front hubs at the same time, which is generally recommended, so some of the stuff below is doubled...

This is off-topic, but before starting this repair, wash your wheels and brakes really well with some wheel cleaner (like Black Magic) and a garden hose so you don't have a bunch of crap falling in your face as you work.
Nitrile Coated Work Gloves... these are awesome and you're going to need a pair of gloves of some kind, and they are going to get filthy.
You'll need a pair of needlenose pliers to pinch the ↧ (plastic arrowhead) that holds the sensor to the mounting bracket in order to remove it.
at least an 8-inch C-clamp or larger. We didn't have a c-clamp large enough (I would guess mine was 6 inch), so we had to resort to shoving pieces of wood in the calipers once we got them off. The front GXP calipers are huge! I'm not sure if you'll need a 10-inch one or not.
Some reasonably thick wire for supporting the brake caliper or brake caliper hooks.
You'll need a jack, jack stands, etc. Look at my How to Install a Transmission Cooler on a GXP page for links to those. Make sure to put on the parking brake with your left foot before jacking the car up. Putting some wood behind the rear tires is a good idea, but the brake is essential.
You're going to have to remove the front wheels, so you either need an impact wrench or you're going to need a lug nut wrench. If you use a lug nut wrench, make sure to loosen all 5 lug nuts a little bit before jacking the car up. Even with the transmission in park, our front wheels still turn, and you'll never get them off without an impact if you already lifted the car and are trying to remove them manually. I don't recall the size of our lug nuts, so I'm not providing a link to a lug nut wrench, in case I select the wrong size.
The front caliper bolts for GXPs are discontinued (as far as I can tell) and not possible to find, so hopefully yours are in good shape, because you'll need to reuse them. If they are in bad shape (rusted), try to do some research in advance so you can hopefully buy some new bolts before you get started. The bolts I am talking about are only visible on the back side. If your car doesn't have much rust (or any), just go with the assumption that you don't need new ones.
You'll have to buy Loctite Threadlocker (the blue type) so you can reuse the brake caliper bolts.
(6 total bolts, so 2 orders of) DORMAN 917503 bolts for the wheel hubs (you're a fool if you don't replace these, they are what hold the wheels to the car and the service manual repeats multiple times to never reuse these) NOTE: your hubs you order might come with replacement bolts, make sure to read what your hubs come with when ordering them. The Mevotech ones I used came with these.
You'll need a 34mm impact socket for the axle nut. You can use an impact socket on a ratchet, but you can't use a regular socket on an impact gun, so get an impact socket whether you own an impact or not so you never have to own both types of sockets.
I also ordered a 33mm impact socket because the OEM axle nut is 33mm. Your car may or may not still have the OEM 33mm size nut on it. Mine did, despite my car already having both hubs replaced by a Pontiac dealership in 2010, so I'm glad I purchased both the 33mm and 34mm.
You'll need a 1/2" breaker bar for removing the axle nut. You might be able to do without it, but good luck if you try! I don't think you're supposed to use an impact on it, even for removing the nut.
You'll need a drift or something similar (maybe a big flat head screwdriver would work if you don't want to buy one) to shove into the brake rotor to prevent it from rotating as you remove (and install) the axle nut. On a GXP, there's not a specific slot on the front caliper for sticking a drift or flat bladed tool into the caliper, so you have to use one of the gaps in the edge of the rotor. I don't know about regular Grand Prix brakes...
(2 orders of) DORMAN 615144 axle/driveshaft nuts (in case the ones on your car look terrible due to the last person using an impact wrench on it... which might be why you're having to replace your hubs if they aren't that old...). Again, the Mevotech hubs I ordered came with new ones, so I didn't have to buy them separately. I'd recommend installing new ones no matter what. One of mine definitely looked like it was installed with an impact because it was ridiculously tight.
a torque wrench that has a range of at least 30 lb ft and 120 lb ft to cover the different specs you'll encounter in this repair. You don't want to mess up your brand new hubs with an impact wrench do you? You CANNOT do this repair without a torque wrench. If you don't own one and refuse to buy one, DO NOT DO THIS REPAIR YOURSELF. You will be much better off if you have a ratcheting one that isn't very long. We had a hell of a time using an old-school type without a ratcheting head. The handle was too long to make the job easy and quick. BUY A SHORT ONE.
13mm, 15mm, and 16mm metric sockets
1/2 inch extensions... you cannot get those 3 hub bolts off without extensions.
3/8" To 1/2" Socket Adapter... you'll likely want one of these unless you own sockets in both 3/8" and 1/2" to complete this job. If your torque wrench is a 3/8" you'll need the opposite adapter in order to install the axle nut. These are handy to have.
a T-30 torx 3/8 inch bit (here's a 1/2 inch drive one if you prefer) to remove the brake rotor's screw. The service manual does not mention this. You're technically supposed to torque the screw to 13 lb ft when reinstalling it, but we found that to feel so tight that we were worried the head would snap off the screw, so we did not tighten it that tight.
and most importantly... you're going to need 2 new hubs. If you want to go with the OEM AC Delco one, the part number for a Grand Prix GXP's front hub is ACDELCO FW293 and this is the main listing on Amazon. You'll need two of these if you're doing both front right and front left hubs. There's also an Amazon Prime listing for this same ACDELCO FW293 with free shipping and returns for Prime members but it is a little more expensive (at the time I am writing this). I did not use AC Delco ones, because Mevotech has produced a much higher quality version. (If Amazon doesn't have it, get it from Rock Auto).

Should you go with OEM AC Delco hubs?

People on Amazon are complaining about the "made in Korea" AC Delco ones now that they are now manufactured there. I don't know if there's any credibility to their complaints or not. A lot of people probably don't own a torque wrench and just ruin everything they install and then blame the product. However, what made me want something different, was just how high quality a different brand looks (particularly the sensor cable) and how it includes all the mounting hardware I was going to have to buy separately. I'm talking about the MEVOTECH TXF513179, which often goes out of stock from Amazon... but is available from other retailers like Rock Auto.

Check out a little side-by-side competitive comparison.

MEVOTECH TXF513179

Mevotech Titan-XF ultra premium hubs are engineered with cutting edge improvements for working truck and SUV Applications.

includes mounting bolts, sensor clip, axle nut, and wheel studs
the sensor is fully enclosed to protect it from the elements
there's a surface coating on everything to prevent rust and corrosion between the brake rotor and hub
there's an additional seal on the brake side to protect internal rolling elements
the flanges are thicker than OEM to provide more stability and protection for the internal components, which will help guard against road vibration and harshness

The blue coating makes the bolts look like they are made of plastic LOL, but I thrilled with them. You can't see any of the blue once the wheels are mounted anyway. The price through Rock Auto is actually cheaper than the OEM AC Delco price too. Certainly cheaper than buying the AC Delco, then separately buying the mounting bolts and axle nut. There's not a single review on these on any website, so I guess I'll be the guinea pig. You can read more about this product on Mevotech's website.

ACDELCO FW293

GM OE parts are the true OE parts installed during production by GM—designed, engineered, and tested to rigorous standards and backed by GM.

includes sensor clip and wheel studs
the sensor is... well... there... with a piece of something loosely around it
there's nothing special to say about it, except that it should be identical to what your GXP originally had on it from the factory
it's going to rust and corrode just as much as your original one has, but how much does the appearance of this hidden piece matter to you?

Normally I'd order this, because I generally prefer OEM parts because they always fit. But the way the Mevotech one has the sensor wire completely encased... I chose it instead.

ACDELCO 513121A

ACDelco Gold parts are the high-quality alternative to OE parts, manufactured to meet GM expectations for fit, form, and function and backed by General Motors.

includes sensor clip and wheel studs
the sensor is there and wrapped in an old Band-aid that washed up on a beach
this has surely got to be a cheaper version of the OE AC Delco one... it doesn't look like an improved, deluxe one to me

I've encountered AC Delco Gold parts here and there throughout the years, and they honestly just confuse me. I've never bought any because of it. The name implies higher quality, but they seem like an economical product instead. They are always cheaper in price, and visually, the few parts I've looked at online look worse and/or like they don't come with everything that the OE AC Delco products do. Sometimes they even have different dimensions than the OEM AC Delco parts, like they were made to be lighter weight. They just confuse me overall. I don't understand why they exist. Wouldn't AC Delco make more money (by spending less money) if they just produced one version of a part instead of one version plus a cheaper version?

Received my MEVOTECH TXF513179 hubs

I received my Mevotech TXF513179 front hubs for my GXP 6/21/21. They look really well made and the coatings to prevent rust and corrosion are super cool. I really like how the sensor is completely sealed and protected on this one. The blue coatings do make the bolts and nut look like plastic, but they are definitely metal. The blue won't be visible once the wheels are back on.

Photos from the process

I don't intend on writing my own "how to" guide, because the service manual excerpts I created in the PDF above (and below) are pretty much all you need. I will, however, show some pictures I took and caption them.

How long did the process take?

Well, we had to go to Autozone to get some blue Loctite and a 3/8" to 1/2" adapter (for twice the price of one on Amazon), and we also ate lunch, so I'll have to guess. We also only had a very long handled old school torque wrench in the 1/2 inch size to use, and that made the entire process take longer. I'd guess around 4 to 5 hours if we worked nonstop. If you have a shorter torque wrench, you can probably get it done in around 3 hours. The first hub was tricky, but by the time we had that one figured out, we knocked the other one out two or three times faster. As long as you have a second person to help you, you can very easily get both replaced in half a day. You'll have a hard time if working alone... that's a lot of steering wheel turning and axle pushing to handle by yourself.

Download the PDF if you haven't already

Driver's side front wheel removed. Take note of the T-30 torx screw and the OEM 33mm size axle nut.

Like I said above, we didn't have a large enough C-clamp, but we were able to shove 2 pieces of wood (that added up to the thickness of the brake rotor) into the caliper, and used wire to support it on the spring.

Rotor and axle nut removed...

Old hub removed. This one wasn't wiggling as bad as the passenger side one, so we started with this one. It didn't fight us as much as the other one did. The 3 bolts were difficult to remove with a 1/2 inch ratchet due to the lack of space. Frankly, they were difficult to remove with a 3/8 inch ratchet as well due to the tie rod and other things getting in the way. We had to turn the steering wheel often to get enough room. One of us would often have to hold the brake caliper higher to get it out of the way of the person trying to undo the bolts.

Old AC Delco hub compared to new MEVOTECH TXF513179. I didn't take very good comparison pics because it was hot outside and we were in a hurry. Take note of how the Mevotech one has a really well shielded sensor and some design improvements over the original AC Delco design to keep internal components from getting dirty.

It's hard to tell, but the design was a little different on this side too. The Mevotech one was a bit thicker to "provide more stability and protection for the internal components, which will help guard against road vibration and harshness." It fit the car perfectly and didn't give us any trouble at all when we went to install it.

The only caliper bolts I could get from Rock Auto were for the rear, and they were not the right size, so we had to reuse the old ones. I don't know the size of them. My dad cleaned them up with a brush and put blue Loctite on them when reinstalling them.

New axle nut, new hub bolts, and rotor put back on. Again, the torx screw is supposed to be tightened to 13 lb ft according to the service manual, but we were worried it would snap off if we did that, so we did not go that tight. We did, however, tighten all these other bolts and the axle nut to the proper torque specs (as you should too). Take note that the Mevotech nut is 34mm.

If you have the time, it's a good opportunity to clean up the inside of the wheels while they are off. I didn't have time, but my favorite cleaner is Black Magic No Scrub Wheel Cleaner.

Caliper back on.

Everything torqued properly and finished. Let's move on to the next one!

This hub was the one with the obvious problem. Not only did it rock back and forth when manually tested while the wheel was on, but it was the one that triggered the error code 3 times over 5 months. The lubricant inside the old hub must have leaked out. It had a smell to it. The grooves were full of gunk. We cleaned this driveshaft end up with mineral spirits and an old toothbrush and then installed the new hub and finished the job the same as the other side.

Are you happy with the Mevotech hubs?

So far, yes! The car is driving smoother, more accurately, and better than it has in many years. Everything feels tight and smooth now. I never noticed how much it felt like my wheels were falling off back when I had the old worn out hubs on the car.

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