Question about Hummer H2

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I have a H2 2005 that keeps on giving me problems when decelerating from speeds higher than 50mph when braking the pedal is rock hard. I have had the servo unit on the brake replaced but no luck. I have also had the oil system cleaned out, no luck. PLEASE help it has set me back 3000 dollars in repairs and parts.

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  • Hummer Master
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The servo unit is replaced.But it still indicates vacuum problem.Get the servo pressure, the master cylinder the brake pads, the servo air leak and servo suction checked.Bleed the brake lines, there is air.If servo unit vacuum pressure checked ok and there is no air block then its brake master cylinder problem.------- This should help.Thanks.Helpmech.

Posted on May 21, 2011

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2.7 s type brakes not working as they should they are ok when you start breaking but when you are down to about 10mph the pedal becomes very hard to push and the car trys to roll on ?


It is possible the problem is ABS related but could equally be a problem with the vacuum servo or brake booster or the "supply" of vacuum.

Certainly best practice would be to begin by ensuring the brakes at each wheel are in good order.

Test the brake servo by pressing the brake pedal vigorously several times while stationary with the engine off. The pedal should then feel higher than usual and rock-hard.
Apply the footbrake with a moderate force and start the engine without using the accelerator pedal, if possible. The brake pedal should be felt to pull itself down under your foot immediately the engine starts and stop pulling down in just two or three seconds, maybe just a second or two more if it is a diesel model.

Release the brake, allow the engine to idle for a few seconds longer and switch off. Listen carefully in the resulting silence for the sound of air leaking. This might have to be repeated several times in order to listen under the dash and in the engine compartment around the brake booster and vacuum lines. A short piece of garden hose used as a listening tube can be useful.

Once a servo has been charged with vacuum, in the absence of leaks, it should remain charged for a long time if the brake is not used - certainly hours but often months or even years is not unusual. Aplly a moderate pressure to the brake pedal and a shhhhh... sound should be heard that lasts about a second and then stops. Increase the pedal pressure and another shhhh sound and stop.

If all tests ok you can be reasonably confident the brake booster and vacuum lines are in order though it is still possible the vacuum supply is insufficient for sustained braking. A road test on a clear and safe downhill route will determine if this is so. Make a rapid series of brief brake applications at a constant speed of around 30mph and the braking effort and the feel of the pedal should remain consistent and if it does not it indicates restricted supply pipes or hoses, poor engine tune, incorrect idle speed (petrol models) or a worn or inefficient vacuum pump if it is a diesel.

Jul 23, 2016 | 2006 Jaguar S-Type 2.7

2 Answers

Uplander shake when braking at high speed


It can be issue with brake system alignment.Get the brake assembly checked.Something is not right and out of its way causing these problem.----------
Click the help links mentioned below and go with the troubleshooting solutions to confirm what is exactly faulty in your case:-----Click the link :----Car shakes like the wheels are going to fall off http://technoanswers.blogspot.com/2012/11/car-shakes-like-wheels-are-going-to.html
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CAR BRAKE PROBLEMS



It can be issue with master cylinder or the problem is there is still some air there in the system,that has to be bleed.Or else the parts replaced are not aligned properly/.I suggest everything back.


There are few help links mentioned below to troubleshoot the issue.


Click the link below and follow its procedure:-----


All types of brake problems and repairs http://howtobyme.blogspot.com/2011/11/abs-and-service-light-comes-on.html

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Brake Fade Issue? http://whoisbyme.blogspot.in/2012/07/brake-fade-issue.html

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Brake System Troubleshooting? http://technoanswers.blogspot.com/2011/11/brake-system-troubleshooting.html

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Car Brake lines have no pressure? http://schematicsdiagram.blogspot.com/2011/12/car-brake-lines-have-no-pressure.html

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Car Brakes Dragging? http://repairhelpcenter.blogspot.com/2011/12/car-brakes-dragging.html

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Car Brakes grabbing? http://repairhelpcenter.blogspot.com/2011/12/car-brakes-grabbing.html

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Car Brakes Making Noise? http://repairhelpcenter.blogspot.com/2011/12/car-brakes-making-noise.html

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Car Brakes Pulling? http://repairhelpcenter.blogspot.com/2011/12/car-brakes-pulling.html

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Pulsating Brake Pedal? http://repairhelpcenter.blogspot.com/2011/12/pulsating-brake-pedal.html

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Spongy brake pedal? http://repairhelpcenter.blogspot.com/2011/12/spongy-brake-pedal.html

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Hard Brake Pedal? http://repairhelpcenter.blogspot.com/2011/12/hard-brake-pedal.html

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Fading Sinking Brake pedal?

http://whoisbyme.blogspot.in/2012/06/fading-sinking-brake-pedal.html

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Feels Like Brake pedal Pulsating http://repairhelpcenter.blogspot.in/2012/06/feels-like-brake-pedal-pulsating.html
============These will help.Thanks.

Nov 23, 2012 | Chevrolet Uplander Cars & Trucks

1 Answer

Obd2 system rediness status won't clear so I can run the smog test due to replacing the battery.


takes a long time to run the rediness test since there are 6 different tests to complete...

PROCEDURE 1
EVAPORATIVE EMISSION SYSTEM LEAK MONITOR
Inspection Conditions
Engine coolant temperature: 30°C (75°F) or less (The engine is stopped before the test drive is started).
Atmospheric temperature: 5 - 30°C (41 - 113°F).
Condition of A/T: Selector lever D range.
Fuel remained in fuel tank: 30 - 50% is recommended.
Time required: 16 minutes or less after started the engine.
Drive cycle pattern: One trip monitor (from start to ignition switch to "LOCK" (OFF) position. Well be completed while traveling with the following drive cycle pattern.
Test Procedure
Engine: start.
Accelerate until the vehicle speed is 89 km/h (55 mph) or more.
While keeping the accelerator pedal opening degree constant, keep the vehicle speed at 89 km/h (55 mph) or more and travel for 16 minutes.
Return the vehicle to the shop, then turn the ignition switch to "LOCK" (OFF) position.

PROCEDURE 2
FUEL TRIM MONITOR
Drive Cycle Pattern
Inspection Conditions
Engine coolant temperature: 100°C (212°F) or less.
Atmospheric temperature: -10 - 60°C (14 - 140°F).
Condition of A/T: Selector lever D range.
Time required: 30 minutes or more.
Drive cycle pattern: One trip monitor (from start to ignition switch to "LOCK" (OFF) position). Will be completed while traveling with the following drive cycle pattern.
Test Procedure
Engine: start.
Accelerate until the vehicle speed is 89 km/h (55 mph) or more.
While keeping the accelerator pedal opening degree constant, keep the vehicle speed at 89 km/h (55 mph) or more and travel for 30 minutes.
Return the vehicle to the shop, then turn the ignition switch to "LOCK" (OFF) position

PROCEDURE 3
CATALYTIC CONVERTER MONITOR
Drive Cycle Pattern
Inspection Conditions
Atmospheric temperature: -10°C (14°F) or more.
Condition of A/T: Selector lever D range.
Engine coolant temperature: Not set.
Time required: 16 minutes or more.
Drive cycle pattern: One trip monitor (from start to ignition switch to "LOCK" (OFF) position). Will be completed while traveling with the following drive cycle pattern.
Test Procedure
Engine: start.
Accelerate until the vehicle speed is 89 km/h (55 mph) or more.
Travel for 300 seconds or more while keeping the vehicle speed at 89 km/h (55 mph) or more.
Decelerate until the vehicle speed is within 80 km/h (50 mph) or less.
While traveling at 56 - 80 km/h (35 - 50 mph) for 10 minutes or more, fully close the throttle at least once in 2 minutes and decelerate for 10 seconds or more.
Do not repeat deceleration too often.
Vehicle speed may go below 56 km/h (35 mph) after the deceleration.
Stopping and braking are permitted. (If stopped or drive at 56 km/h (35 mph) or less for more than 5 minutes the monitoring may be stopped. In this case please restart monitoring from the beginning.)
After completing the above deceleration, bring the vehicle speed back to 56 - 80 km/h (35 - 50 mph) and keep it in the range until starting the deceleration again.
Repeat the above deceleration at least 5 times.
Return the vehicle to the shop, then turn the ignition switch to "LOCK" (OFF) position

PROCEDURE 4
HEATED OXYGEN SENSOR MONITOR
Drive Cycle Pattern
Inspection Conditions
Engine coolant temperature: 100°C (212°F) or more.
Atmospheric temperature: -10°C - 60°C (14 - 140°F) or more.
Condition of A/T: Selector lever D range.
Time required: 16 minutes or more.
Drive cycle pattern: One trip monitor (from start to ignition switch to "LOCK" (OFF) position). Will be completed while traveling with the following drive cycle pattern.
Test Procedure
Engine: start.
Accelerate until the vehicle speed is 56 - 80 km/h (35 - 50 mph).
While keeping the accelerator pedal opening degree constant, keep the vehicle speed at 56 - 80 km/h (35 - 50 mph) and travel for 16 minutes or more.
Stopping and braking during this operation are permitted. Keep the accelerator opening degree constant for 1 minute or more after each acceleration.
Return the vehicle to the shop, then turn the ignition switch to "LOCK" (OFF) position

PROCEDURE 5
EXHAUST GAS RECIRCULATION (EGR) SYSTEM MONITOR
Drive Cycle Pattern
Inspection Conditions
Engine coolant temperature: 100°C (212°F) or less.
Atmospheric temperature: 5 - 60°C (41 - 140°F).
A/C switch: OFF.
Condition of A/T: Selector lever D range.
Time required: 16 minutes or more.
Drive cycle pattern: One trip monitor (from start to ignition switch to "LOCK" (OFF) position). Will be completed while traveling with the following drive cycle pattern.
Test Procedure
Engine: start.
Accelerate until the vehicle speed is 56 - 80 km/h (35 - 50 mph).
While traveling 16 minutes or more at 56 - 80 km/h (35 - 50 mph) with engine speed 2,000 r/min or above, fully close the throttle at decelerate for 5 seconds or more until the engine speed reaches 1,000 r/min or under.
Do not repeat deceleration too often.
Stopping and braking are permitted (Rapid deceleration and sharp steering are not permitted).
After completing the deceleration, bring the vehicle speed back to 56 - 80 km/h (35 - 50 mph) and keep it in the range until starting the deceleration again.
Repeat the above deceleration at least 8 times by fully closing the throttle valve.
Return the vehicle to the shop, then turn the ignition switch to "LOCK" (OFF) position

PROCEDURE 6
OTHER MONITOR (Main Components, Sensors & Switches, Wire Breakage & Short Circuit)
Drive Cycle Pattern
Inspection Conditions
Engine coolant temperature:
100°C (212°F) or less (Except engine coolant temperature sensor monitoring).
30°C (86°F) or less (Engine coolant temperature sensor monitoring).
Atmospheric temperature:
5°C (41°F) or more (Except engine coolant temperature sensor monitoring).
-10°C (14°F) or less (Engine coolant temperature sensor monitoring).
Condition of A/T: Selector lever D range.
Time required: 21 minutes or more.
Drive cycle pattern: One trip monitor (from start to ignition switch to "LOCK" (OFF) position). Will be completed while traveling with the following drive cycle pattern.
Test Procedure
Engine: start
Accelerate until the vehicle speed is 56 km/h (35 mph) or more.
While keeping the accelerator pedal opening degree constant, keep the vehicle speed at 56 km/h (35 mph) or more and travel for 16 minutes or more.
Return the vehicle to the shop.
After stopping the vehicle, continue idling for 5 minutes, and then turn the ignition switch to the "LOCK" (OFF) position. Moreover, the vehicle should be set to the following conditions for idling.
A/C switch: OFF
Lights and all accessories: OFF
Transmission: Neutral

Sep 15, 2010 | 1998 Mitsubishi Eclipse

1 Answer

ABS light stays on sounds like a abs pump is staying on. Is there a pump for the abs system?


There is no seperate pump. The following lines will give you more details

Braking force and the tendency of the wheels to lock up are affected by a combination of factors such as the friction coefficient of the road surface, and the difference between the vehicle speed and the road wheel speed. The ABS prevents the road wheels from locking up during heavy braking by controlling the vehicle's brake system hydraulic pressure.
During normal braking, as the rotational speed of the wheel falls, no electric current flows from the ECU to the hydraulic unit. The solenoid valve is not energized. The brake master cylinder hydraulic pressure is applied to the brake unit, and the ABS is not involved. However, even though the ABS is passive during normal braking, its control module is constantly monitoring for rapid deceleration of any of the wheels.
If a wheel-speed sensor signals severe wheel deceleration - which means the wheel is likely to lock up - the ECU sends a current to the hydraulic unit. This energizes the solenoid valve. The action of the valve isolates the brake circuit from the master cylinder. This stops the braking pressure at that wheel from rising, and keeps it constant.
If the sensors signal the wheel is still decelerating too rapidly, the ECU sends a larger current to the hydraulic unit. The armature moves even further and opens the valve. It opens a passage from the brake circuit. Brake fluid is sent from the brake circuit back to the master cylinder. Pressure in the brake caliper circuit is reduced so that the wheel is braked less heavily.
If the wheel sensors indicate that lowering the brake pressure is letting the wheel accelerate again, the ECU stops sending current to the hydraulic unit and de-energizes the solenoid valve. This lets the pressure increase, so that the wheel is again decelerated.
This cycle repeats itself about four to six times per second.
It is normal in an ABS for the valves in the hydraulic control unit to keep changing position as they change the brake pressure that’s being applied. These changes in position may cause rapid pulsations to be felt through the brake pedal.

Jun 06, 2010 | 2003 Chevrolet Silverado 1500

1 Answer

1999 jeep grand cherokee tacometer reading???


Cruising rpm even after the OD has engaged has a lot to do with the differential gear ratio and tire size.
There will always be a variation between different vehichles due to that alone.
To see if the OD is working, at about 50mph, lightly touch the brake pedal. If the rpms increase for a moment then the OD was engaged. (touching the pedal momentarily disengages it...good thing to know when hill climbing!

Apr 27, 2010 | 1999 Jeep Grand Cherokee

1 Answer

1997 Honda Civic did not pass smog due to O2 sensor heater fault failure, sensor 1, bank 1. If I replace the sensor, how do I get the check engine light reset?


the best way to reset it is with a scan tool.
disconnecting the battery for one minute will also remove the code.BUT
if your smog test uses an OBD scan as part of the process,then there will be a problem,because the monitors will not have been set,as they are reset if the battery is disconnected..
most tests allow only one monitor missing,and not the catalyst .
A drive cycle will have to be done to set the monitors.
Typically cold start coolant temp less than 50F,idle for 2 minutes no air condition, accelerate at half throttle to 50mph then drive 3 minutes with a/c on at 50mph steady.decelerate to 10mph without using brakes..Accelerate to 60mph and drive for 5 minutes at steady speed without a/c
deccelerate without braking and drive for 1 minute at 40mph.
stop the car ,use braking.
Shut off the car and add 4 gallons of gas.do not shut off the car for more than 5 minutes.
drive in 3rd gear or overdrive off with rpm 3000 for 1 minute.
decelerate to 10mph.without braking
accelerate to 40 mph in 4th gear.,or overdrive on
decelerate without braking to 10mph.
test complete.
this will set the o2 sensor heater ,o2 sensor,catalyst,evap purge.and the other monitors.

Feb 26, 2010 | 1997 Honda Civic

2 Answers

Everytime im driving slow and i brake my brakes grind and i have to press hard to come to a stop. it rarely happens when im going at higher speeds although it has happened. Whats the problem?


normally grinding and a hard pedal mean excessive wear on the brake pads, you wont feel it as much at higher speeds, at low speads its more previlant due to the pressure......check front pads first, the rear ones usually wear a lot slower

Aug 10, 2009 | 2007 Chevrolet Aveo Sedan

1 Answer

I have a shimmy in mySteering wheel not all the time it comes on randomly.


In absence of more information, this is usually an symptom of warped brake rotors. A rotor can build up enough heat in a hard stop to be bendable especially with the high hydrolic pressure a brake pad can bring to bear. Simply, If you keep the brake pedal depressed hard after a hard/long stop it can warp the rotor. (NOTE: at a hard stop, as soon as possible let the car creep forward a few inches at a time so the brake pad won't be on any one spot too long, plus keep light brake pressure --only enough to keep the car from rolling). The warped rotor causes the brake pad and caliper to float too far from the rotor and you won't feel the shimmy until you apply brakes. Under brake pedal pressure each time the wheel rotates under brake pressure the rotor and caliper will rapidly vibrate a few millimeters to each side giving the sensation of a shimmy in the sterring wheel. Most of the time this can be corrected by having the rotors resurfaced( aka Turned)

Out of balance or out of round tires can also cause a shimmy but should occur at a given speed range. Warpped rotor shimmy occurs during deceleration.

Aug 04, 2008 | 2001 Dodge Grand Caravan

1 Answer

Loud squeaking brakes.


If they are wearing down, they may squeak, and some brakes have a metallic part that will come in contact with the rotor when the wear gets to a certian point making an awful squeaking sound telling you that mabe you should change 'em soon, eh

Jun 17, 2008 | 1995 Ford Escort

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