H.A.C not working as designed.

[toyo]

On my new to me 08 I don't feel this is operating like it should or like my 04 model used to. Here is my scenario that I am doing where it should be working.

To get into my office/building I pull up a ramp that is about 20 feet long and 5 feet high at the highest point at the entrance. I pull to the top, get out and open a roll up door. Get back into the car, put into drive and as soon as I put my foot on the gas my VSC system starts blinking and activates. It should not be doing this as it is not slippery at all. I tried to see what happened if I activated the HAC system and it did not hold the vehicle as designed. I have no codes for any systems at all. Curious if anybody has experienced this at all? Search came up with nothing.....

 

[BlackWorksInc]

Are you confusing HAC (Hill Assist Control) with DAC (DownHill Assist Control).

HAC is passive and functions to prevent the vehicle rolling back down a hill when in Drive and/or applying light throttle and will activate the VSC/TRAC system to hold it in place irregardless of "slipperyness" as it is a function of inclination and the vehicle sensing itself rolling backwards.

DAC functions only at low speed and in low gear to control the vehicle going down in sharp downhill situations. You are actually supposed to let the vehicle do the braking for you when using DAC (its a very awkward experience) and is again more tied to inclination and rolling downhill (in this case nose first vs. backwards.)

 

[toyo]

I am on an incline going up, so no I'm not confusing the two. In my situation the HAC should be holding the vehicle from going backwards. My 04 did without fail. What's puzzling is I have no other symptoms of a problem such as lights or stored codes.

 

[nevada]

On my new to me 08 I don't feel this is operating like it should or like my 04 model used to. Here is my scenario that I am doing where it should be working.

To get into my office/building I pull up a ramp that is about 20 feet long and 5 feet high at the highest point at the entrance. I pull to the top, get out and open a roll up door. Get back into the car, put into drive and as soon as I put my foot on the gas my VSC system starts blinking and activates. It should not be doing this as it is not slippery at all. I tried to see what happened if I activated the HAC system and it did not hold the vehicle as designed. I have no codes for any systems at all. Curious if anybody has experienced this at all? Search came up with nothing.....

that's IS the HAC activating. you're saying when those lights come on, it still rolls back?

you said you "activated the HAC", what exactly did you do differently to activate it, if not the above?

 

[toyo]

that's IS the HAC activating. you're saying when those lights come on, it still rolls back?

you said you "activated the HAC", what exactly did you do differently to activate it, if not the above?

I "activated the HAC system by taking my foot off the brake and it does not hold. This is the only way to use the system. When I apply the gas that's when I hear the brake booster and the ABS pump doing it's thing. Which it should not be doing.

The system is designed to not allow the vehicle to roll backwards from the time you release your foot from the brake pedal to the gas pedal. My 04 did this in perfect silence without you ever really knowing that it was functioning.

Tomorrow I will take some shots on what exactly it is doing to better describe it.

 

[toyo]

This is a description from a Toyota press release.

The basic function of the HAC system is to help increase control on steep
upgrades and stopping and starting on slippery surfaces. The HAC system is designed
to help prevent the vehicle from rolling backward or slipping sideways during transition
from a stopped position to climbing an upgrade. The system is automatically activated
when the transmission is in any forward gear. The HAC system controls the brakes to
help stop the individual wheel or wheels, which helps prevent the vehicle from rolling
backward or slipping sideways.
Toyota HAC and DAC 2-2-2-2-2


The HAC system determines the driver’s intended vehicle direction from the
present gearshift position of the transmission, the moving direction of the vehicle wheels,
and the wheel speed of the four wheels through the use of active wheel sensors. When
backward rolling or slippage occurs, the HAC system is automatically activated. Upon
activation the HAC system gently applies the brakes. The HAC system measures the
necessary brake pressure of each wheel to help prevent individual wheels from locking
and causing vehicle slippage.

 

[BlackWorksInc]

Your earlier statement doesn't make any sense when you look at what you just posted above, HAC & DAC are purely controlled via the ABS system and Hydraboost Unit. If HAC kicked in you'd hear the ABS system functioning to some extent. The system will take over, use the ABS solenoid pack to actuate the brakes and clamp them down enough to stop the vehicle from rolling back, the resultant use of stored hydraulic force will cause the hydraulic accumulator pump to kick in momentarily and thus you'd get all the whirring, buzzing noises of the Hydraboost unit doing its job

If HAC kicks in it should sound similar to the ABS kicking in, but not as aggressive; more of a "pump noise running, some solenoid noise." What you may have been perceiving as HAC was merely the V8's low end torque resisting inclination. i.e. the vehicle wasn't creeping forward as it does on level ground with the foot off the gas, but simply preventing gravity from pushing the 4Runner backwards. I experience this regularly in my '04, but it is not a function of HAC as much as it is a result of the vehicle's drivetrain.

 

[toyo]

Your earlier statement doesn't make any sense when you look at what you just posted above, if HAC kicked in you'd hear the ABS system functioning to some extent. The system will take over, use the ABS solenoid pack to actuate the brakes and clamp them down enough to stop the vehicle from rolling back, the resultant use of stored hydraulic force will cause the hydraulic accumulator pump to kick in momentarily and thus you'd get all the whirring, buzzing noises of the Hydraboost unit doing its job

If HAC kicks in it should sound similar to the ABS kicking in, but not as aggressive; more of a "pump noise running, some solenoid noise." What you may have been perceiving as HAC was merely the V8's low end torque resisting inclination. i.e. the vehicle wasn't creeping forward as it does on level ground with the foot off the gas, but simply preventing gravity from pushing the 4Runner backwards. I experience this regularly in my '04, but it is not a function of HAC as much as it is a result of the vehicle's drivetrain.

I see what your saying, but this is not normal. I am wondering if the incline is too much for the system to handle. I am going to test it out lower down the ramp and see what it does.

I appreciate your comments and helpfulness. We'll get it figured out. I think once you see some pics of what I am feeling you will have a better idea of what I am trying to describe. I guess I will have to do a small video clip of the noises and lights.

I am not looking for a problem believe me, I just don't think this is correct in what it is doing.

 

[nevada]

I "activated the HAC system by taking my foot off the brake and it does not hold. This is the only way to use the system. When I apply the gas that's when I hear the brake booster and the ABS pump doing it's thing. Which it should not be doing.

The system is designed to not allow the vehicle to roll backwards from the time you release your foot from the brake pedal to the gas pedal. My 04 did this in perfect silence without you ever really knowing that it was functioning.

Tomorrow I will take some shots on what exactly it is doing to better describe it.

my 06 works just like this.

as far as I can tell, its doing what its supposed to.

 

[RobRomero]

I’ve got the same problem

I see what your saying, but this is not normal. I am wondering if the incline is too much for the system to handle. I am going to test it out lower down the ramp and see what it does.

I appreciate your comments and helpfulness. We'll get it figured out. I think once you see some pics of what I am feeling you will have a better idea of what I am trying to describe. I guess I will have to do a small video clip of the noises and lights.

I am not looking for a problem believe me, I just don't think this is correct in what it is doing.

Did you solve the problem? Thanks