Brake Troubleshooting

[vicnation]

I have a 2006 Denali XL with about 172K miles. I need some advice/help troubleshooting the following issues. There are no codes in the system. The accelerator pedal and the throttle position switch have already been replaced. The throttle body has been cleaned. When I try to accelerate from a dead stop, there is a brief delay after pressing the pedal. There is also some kind of mechanical sound during the delay before it finally takes off. The sound seems to come from under the drivers floorboard or on the firewall. When the noise stops, the vehicle accelerates as normal. When I accelerate from a slow roll, I sometimes don't get the delay, and there is no noise if there is no delay. The noise sounds like a light scraping on plastic or a rattling sound.

When I slow to a stop, I get a groaning noise in the same area as the noise described above and my brake pedal rises against my foot.

I'm wondering if these issues are related. I do have a leak at my hydroboost but even when the fluid is full, the noise occurs. Could my ABS be an issue? Could it be holding my brakes even after I release the brake pedal to try to accelerate? What would cause the pedal to move back against my foot? Any help/advice would be appreciated.

 

[swathdiver]

Sure seems that way. A Tech-2 type tool will assist you in diagnosing this.

 

[Fless]

Sure seems that way. A Tech-2 type tool will assist you in diagnosing this.

^^ THIS. Guessing an ABS or wheel speed sensor issue. You need a scanner on it that will read the ABS and body codes, the cheap code readers read only engine and emissions codes.

 

[nonickatall]

Okay I'm speculating...

You have broken front wheel beering hub or hubs which effects the ABS Sensor which is used as well for the tracking control and the tracking control or Abs are active when you accelerate...

The noise comes from under your seat because under your seat sits the abs control unit with the valves which make this stuttering noise..

And you have no error code, because you receive and error code when a sensor is not available anymore, but for the system it looks like that everything is okay, but your wheels are not turning (virtually) simultaneously. Means the system detect through wrong data, one wheel is slower, meas the other is slipping.

Can also be a problem with the control unit itself, but most likely, from my view, are the front wheel beering hubs..

 

[Fless]

The ABS modules in these do tend to go bad, but don't condemn it until you have collected some data and evaluated that. It's one thing of several that could cause the issue.

 

[Scottydoggs]

you'll need a high end scanner that can read abs codes. best to always see what codes there then work from there, everything else is really just a guess. other then making sure abs plugs and installed wires to them are not damaged.

but that actually does sound like the ebcm is broken. my guess.

you can pull the abs fuse from the fuse box, that will kill all abs stuff, tc, stability control, all of it. at least it wont be acting up till its scanned and you can figure out a plan of attack.

 

[vicnation]

Thank you all for the guidance. Is there an affordable scanner that you would recommend?

Also, I forgot to mention that I did replace the front wheel sensors. I did not replace the hubs.

 

[nonickatall]

The problem is, that when the front wheel hubs get play, then the sensor ring moves in a uncontrolled way in relation to the sensor.

That is the main problem, not the sensor itself.

So apart from that your sensor is defective, it makes no difference when you change the sensors, but not the bearing hubs.

When the bearing hubs are the problem...

 

[Fless]

Did this problem exist before the front wheel speed sensors were replaced? It's best to change the hub and the sensors as one unit; mismatches can occur if only one of those items is replaced. But I wouldn't change a thing until I checked the functionality of all of the speed sensors.

 

[vicnation]

I replaced the sensors due to this problem. It was less expensive than replacing the hubs and I didn't have the money at the time. Is there an affordable Tech-2 type scanner anyone would recommend? I've seen where someone mentioned the Foxwell NT630 Pro, the Foxwell NT630 Plus, the Foxwell NT510 Elite, and the MaxiCom MK808BT Pro. Will any of these work? Any other suggestions for something under $300? Is there a decent scanner that would provide this level of troubleshooting for both GM and other makes of cars?