2001 Tahoe Lunging Forward When Stopped

Hi,

My Tahoe lunges forward when stopped. It's very sporadic and can't be duplicated.

2001 5.3 two wheel drive Tahoe

Conditions:

When stopped in drive with foot on brake

Symptoms:

ABS Light comes on and off randomly as driving
Traction control light comes on and off randomly as driving
This is when somethbing is about to happen but can drive for weeks with nothing happening

Diagnostics:

Full systems diagnostics shows no errors or stored faults
I did the diagnostics myself as did the Chevy dealership

Effect:

The vehicle lunges forward at enough rpm to propel it into the middle of the road.
You press on the brake hard to try to stop the vehicle but the abs kicks in (so it seems) the pedal goes all the way down and shudders
Happens for around 2 seconds every time.

Over the past 2 years this has happened 1/2 dozen times to myself and my wife so I highly doubt we're both accelerating while trying to stop the vehicle.

Also, the first time it happened I replaced a bad hub on the drivers side and it stopped doing it. Started again about a month ago. Too freaked out to drive the car now as it seems to be worsening literally throwing you into cross traffic. Luckily there we no cars or the 60mph cross traffic would have been a direct drivers door hit.

Anyway this is my last ditch effort to try to make sense of it. I plan on buying another SUV this weekend but if this is common and a known issue with a fix, maybe I'll consider keeping it.

Thanks!

this may be just the front hubs rusted fouling the front wheel sensors. with my 2000 sil 4X4 the hub bearing seals rusted out . this then caused the amber ABS light to go on/off intermittently. braking was very intermittent on ABS activation. I do not have traction control.

check the ground connection also under the drivers door on the frame rail as this is the ABS module ground.

the low sensor voltage can get distorted with a bad ground.

Hi,

My Tahoe lunges forward when stopped. It's very sporadic and can't be duplicated.


Thanks!

on the idle problem this maybe the PVC or hoses.a worn pcv or a cracked leaking pcv hose can create idle problems.


also the throttle body/IAC needs cleaning. this controls the idle. if this is dirty restricted binding etc with too much air entering the throttle body can cause high idles.

with too much air entering because the IAC is sticking the computer/pcm increases the fuel which increases the idle RPM so the the mixture is correct.

I would say you have at least two problems.

Yeah, sounds like some unwanted abs activation as stated above. You can try cleaning the sensors themselves, look inside the sensor mount hole at the grease. If its rusted(red in color) the hub needs replaced, although this will not always indicate the bad hub. Basically one of the speed sensors drops out before the truck is stopped causing the EBCM to think you have a lock up condition, activating the ABS.

check for codes sounds like egr valve open

Hi,

My Tahoe lunges forward when stopped. It's very sporadic and can't be duplicated.

2001 5.3 two wheel drive Tahoe

Conditions:

When stopped in drive with foot on brake

Symptoms:

ABS Light comes on and off randomly as driving
Traction control light comes on and off randomly as driving
This is when somethbing is about to happen but can drive for weeks with nothing happening

Diagnostics:

Full systems diagnostics shows no errors or stored faults
I did the diagnostics myself as did the Chevy dealership

Effect:

The vehicle lunges forward at enough rpm to propel it into the middle of the road.
You press on the brake hard to try to stop the vehicle but the abs kicks in (so it seems) the pedal goes all the way down and shudders
Happens for around 2 seconds every time.

Over the past 2 years this has happened 1/2 dozen times to myself and my wife so I highly doubt we're both accelerating while trying to stop the vehicle.

Also, the first time it happened I replaced a bad hub on the drivers side and it stopped doing it. Started again about a month ago. Too freaked out to drive the car now as it seems to be worsening literally throwing you into cross traffic. Luckily there we no cars or the 60mph cross traffic would have been a direct drivers door hit.

Anyway this is my last ditch effort to try to make sense of it. I plan on buying another SUV this weekend but if this is common and a known issue with a fix, maybe I'll consider keeping it.

Thanks!

There is several TSB's on cleaning TBI and reprograming the VCM to correct idle problem.
Also a recall on ABS brake problem.

Have you dealer run vin no for RECALLS and TSB's.

Has the TBI ever been cleaned?
Any ABS recalls done?

Thanks for the replies guys.

The dealer told me all recall work was done or in their words "doesn't look like you need any recall work done". They thoroughly checked the ABS system and found nothing wrong with it.

I'll work on it tomorrow and address all your suggestions. TBI was cleaned at last tuneup (5K miles ago). I'll tear it down completely and go over every bit though.

Interestingly, today as I was driving and going over some speed bumps, the traction control light was turning on and off. This is a major symptom. Any thoughts on this? I feel it's related but don't have a shop manual to follow components and circuits. Maybe grounding out somewhere? No codes as usual... I'll start at the wheel sensors and work back.

Dealer wants to give me only $2K for a trade-in on my immaculate Tahoe with many many extras. I'd rather part it out... between my ent. system, wheels and tranny I can make more than that! sheesh what a ripoff.... this car is flawless except for this problem.

Thanks for the replies guys.

The dealer told me all recall work was done or in their words "doesn't look like you need any recall work done". They thoroughly checked the ABS system and found nothing wrong with it.

I'll work on it tomorrow and address all your suggestions. TBI was cleaned at last tuneup (5K miles ago). I'll tear it down completely and go over every bit though.

Interestingly, today as I was driving and going over some speed bumps, the traction control light was turning on and off. This is a major symptom. Any thoughts on this? I feel it's related but don't have a shop manual to follow components and circuits. Maybe grounding out somewhere? No codes as usual... I'll start at the wheel sensors and work back.

Dealer wants to give me only $2K for a trade-in on my immaculate Tahoe with many many extras. I'd rather part it out... between my ent. system, wheels and tranny I can make more than that! sheesh what a ripoff.... this car is flawless except for this problem.

any 10year old vehicle any condition , the dealership sees this as you screwing them ....you bring a vehicle 10 years or older to the dealership for repairs they at the end, will make you regret paying alot to fix it.

when the sensors loose the pickup voltage because of rust they will act up much more so over any road defects especially at the lower speeds less than 10 mph. also when making turns at low speed abs lt will come on.

Check out alldata.com. May be worth the $20-25 for a year subscription to help you thru this issue.

Good Luck

Check out alldata.com. May be worth the $20-25 for a year subscription to help you thru this issue.

Good Luck

WOW! This is an awesome resource... had no idea it existed! Puchased Tahoe and my 911 that is normally ridiculously priced for shop manuals. :smile: Also saved a few bucks with a coupon from here: http://www.retailmenot.com/view/alldatadiy.com

Cheers!

Thanks for the replies guys.

The dealer told me all recall work was done or in their words "doesn't look like you need any recall work done". They thoroughly checked the ABS system and found nothing wrong with it.

I'll work on it tomorrow and address all your suggestions. TBI was cleaned at last tuneup (5K miles ago). I'll tear it down completely and go over every bit though.

Interestingly, today as I was driving and going over some speed bumps, the traction control light was turning on and off. This is a major symptom. Any thoughts on this? I feel it's related but don't have a shop manual to follow components and circuits. Maybe grounding out somewhere? No codes as usual... I'll start at the wheel sensors and work back.

Dealer wants to give me only $2K for a trade-in on my immaculate Tahoe with many many extras. I'd rather part it out... between my ent. system, wheels and tranny I can make more than that! sheesh what a ripoff.... this car is flawless except for this problem.

If traction control light coming on it has a problem and code.
AS SUGGESTED GET THE THE ALL DATA DIY REPAIR SUB WILL TAKE YOU THREW THE REPAIR.
Check out the tsb's and recalls listed in it on ABS and other stuff..
Bad wiring and rust build up on speed sensors is a good place to start.

Got the alldata sub and went through the wheel speed sensor cleanup and test. Pushing 1.2v (1200mV) on both sides so it checks out. Forgot to test before teardown for comparison.

Cleaned ground under drivers side and also repaired a ground that went from DS firewall to the hood that was broken. Also cleaned another ground from DS firewall to tranny somewhere.... didn't trace it. Cleaned all connectors from EBCM and all other connections I could find while under there.

Noticed a vacuum connection was cracked on the DS fuel rail? so fixed that too. Cleaned throttle body again.

No signs of corrosion anywhere but cleaned anyway. Hubs looked rust free but kind of greasy so cleaned those as well.

So far so good just took a "speed bump" run and no lights show.

We'll see how it goes.

Thanks for your help guys....much appreciated. Will report back either way in a couple weeks.

Today I removed the EBCM and sent it in for repairs. Looks like there is definitely a problem with it. Read in another post about Module Master that does EBCM repair so off it went for $130.... not bad at all.

When I took the EBCM off the hydraulic unit I saw what looks like rust/burn on one of the whatchamacallits (see photos - looks like it got a short - brown/black). Now I'm concerned that might also need repair. No real way to get to the internals to know for sure if that's also an issue. Egh I've never been a parts swapper... would really like to diagnose before I get a new one.

Next logical step is to clean it and look for pitting with a magnifying glass.

Anyone know of any process to test the hydraulic units? Haven't been able to find anything on the topic or even a resource I can sent it to.

Cheers!

Today I removed the EBCM and sent it in for repairs. Looks like there is definitely a problem with it. Read in another post about Module Master that does EBCM repair so off it went for $130.... not bad at all.

When I took the EBCM off the hydraulic unit I saw what looks like rust/burn on one of the whatchamacallits (see photos - looks like it got a short - brown/black). Now I'm concerned that might also need repair. No real way to get to the internals to know for sure if that's also an issue. Egh I've never been a parts swapper... would really like to diagnose before I get a new one.

Next logical step is to clean it and look for pitting with a magnifying glass.

Anyone know of any process to test the hydraulic units? Haven't been able to find anything on the topic or even a resource I can sent it to.

Cheers!

if the dealership put the ABS tester on it to check the valves and read those codes and with your saying they found nothing I would say the abs control module is ok.

the relay in the control module will be replaced with the service you are having as that relay GM put in lacks the ability to handle the 90 amp surge when you start the vehicle each time to test for ABS operation.

with no dtc abs or other codes I would say the front sensors/hubs are the issue.

Just an update on this to help others with a similar problem.

I repaired the EBCM (had blown components not apparent when testing) and also decided to replaced the ABS modulator since 1 looked pitted and I wasn't convinced it was good since a hard stop locked up the wheels (this also bench tested well but it didn't feel right).

I also replaced both front hubs and sensors as they were acting up when I was testing the resistance again... sometimes 1.2volts and other times nothing.

The master cylinder was very gritty and dingy so I swapped that out as well (see my other thread for more details on this).

I also did all the wiring ground work recommended by others on this thread and cleaned out my throttle body again even though I had done a full tune-up not long before.

Cost of repair:
Repaired EBCM: $180 shipped
New ABS Modulator: $156.61 shipped
New Master Cylinder: $50 shipped
New Both Front Hubs + ABS Sensors: $86 shipped
Synthetic Dot3 Brake Fluid: $18 local
Total cost: $487.61
Labor: $0 (6hrs total of my time)

The car is perfect now. On a hard brake, absolutely no locking up and stops better than new! I can now feel the rear brakes working too.... no more nose dives.

There are no symptoms or signs of the lunging problem at all and a I now have a higher, harder and more responsive brake pedal due to the larger bore master cylinder.

I suspect I had multiple issues that contributed to the problem and all of these repairs seem to have corrected it.

Thanks for everyone's help I very much appreciate it! Now for my loose freeway steering... but that's for another thread.

Happy new year!

Just an update on this to help others with a similar problem.

I repaired the EBCM (had blown components not apparent when testing) and also decided to replaced the ABS modulator since 1 looked pitted and I wasn't convinced it was good since a hard stop locked up the wheels (this also bench tested well but it didn't feel right).

I also replaced both front hubs and sensors as they were acting up when I was testing the resistance again... sometimes 1.2volts and other times nothing.

The master cylinder was very gritty and dingy so I swapped that out as well (see my other thread for more details on this).

I also did all the wiring ground work recommended by others on this thread and cleaned out my throttle body again even though I had done a full tune-up not long before.

Cost of repair:
Repaired EBCM: $180 shipped
New ABS Modulator: $156.61 shipped
New Master Cylinder: $50 shipped
New Both Front Hubs + ABS Sensors: $86 shipped
Synthetic Dot3 Brake Fluid: $18 local
Total cost: $487.61
Labor: $0 (6hrs total of my time)

The car is perfect now. On a hard brake, absolutely no locking up and stops better than new! I can now feel the rear brakes working too.... no more nose dives.

There are no symptoms or signs of the lunging problem at all and a I now have a higher, harder and more responsive brake pedal due to the larger bore master cylinder.

I suspect I had multiple issues that contributed to the problem and all of these repairs seem to have corrected it.

Thanks for everyone's help I very much appreciate it! Now for my loose freeway steering... but that's for another thread.

Happy new year!

You are welcome and thanks for posting back how went and the fix.
Did the All Data help?

thanks again with the detailed repair info ..very good post to help other forum members.

MT-2500 the all-data did help some mostly to verify that chevy does have an issue with the ABS/Traction control and their symptoms and repair.

Also I forgot to mention where I purchased all the parts.

* eBay for all the parts listed
* Modulemasters for the EBCM repair
* Autozone for the brake fluid.