How do you rewhy is my brakes locking down while driving?how do i rest the abs system?

The Anti Lock Brake System on a Mercury should store a trouble code that can be read with special equipment to let you know what the system is seeing wrong that caused the light to stay on. This code is usually stored for up to a week even when the light is not on.
It is possible that a low tire is causing the ABS system to think one of the tires is spinning too fast while braking and set the light. A low tire has to spin a little faster to keep up with the rest, which can appear to the computer as an anti lock brake situation or even an error. The correct tire pressure is listed on a sticker in the drivers door jamb.

Hi!

195(width in mm)/60(sidewall height in % of width) R15(rim diameter)

This means, a 195/60 R15 rides lower than a 195/65 R15 tire. Imagine how it would look like when you put these different tire sizes on one car. It can be done but the car will be unbalanced both mechanically and aesthetically. Remember, your car was not designed for different front and rear tire sizes unlike some sports cars.

A 2005 model will most like come standard with ABS as with most cars produced year 2001 onwards.
Just buy 1 tire size for your car. If you wish to change to another tire size, change all the tires.

Good luck!

The noise is normal ( somewhat) Things that can make it happen too often are mis adjusted tire pressure. wrong tires ( all the tires have to be the same size) worn out tires low grip. The ABS system will work normally only if a tire is trying to skid. if the seed senser dectects a tire is going the wrong speed conpared to the others or the car is slowing down faster than the design limites the system will cycle and not turn the light on. If say the back brakes are worn out the fronts may cycle the system as the front is the only thing stopping the car.

BMW MODELS AFFECTED: All with ABS

FAULT: ABS warning light comes on intermittently. Normal troubleshooting procedures find no defect.

Possible Cause: If car has recently had two new tires, or snow tires put on. Sometimes when the car is driven over 50 MPH.

Solution: Check all four tires on the car, make sure they are the same brand, style, and size. Check if
any of the new tires have substantially more tread than the rest. These differences may cause enough
variance in rolling diameters to confuse the ABS control unit, which in turn, gives a false signal to the ABS
warning light.

If that is not the issue, it is most likely the ABS control module failing.

Two most common causes fro brakes to lock are : Contamination on brake linings from a leaking wheel cylinder or axle seal and out of round drums.
If drums are in otherwise good condition they often can be cut on a lathe and trued up. If the material is too thin or the out of round condition is so severe that cutting will make them too thin then they need to be replaced.
If you have an abs system, a malfunction there can also cause that problem. Abs systems are sensitive to different sized tires front to rear but with a 4x4 you should not have that problem as that would also do damage to the transfer case.

Something as simple as a different tire size can cause the abs to go nuts. I even had it where the two tires were the same size. But a different brand name. Each manufacture has their own tire sizing so not all tires a equal in size. Even though it says on the side of the tire that they are the same size.

Sometimes the cooper inside the insulation of the wires going to the sensors corrodes. Especially on the front units. It reads more ohms than normal but not open and is very intermittent. However moving the wires my make it work for a while. That's why replacing bearings seems to fix the problem but it comes back after a while.

You can test the speed sensors yourself...
Front sensor specs:
956 to 1240 ohms in 41 to 110 degree weather
at least 100mV AC (NOT DC!) volts when hub is spun by hand
Rear sensor specs:
950 to 1300 ohms in 41 to 110 degree weather
At least 100mV AC (NOT DC!) volts when hub is spun by hand

Here is some information from service bulletins that could be related to the problem. The traction control, antilock brakes, and tire inflation monitor all use wheel speed sensor input.

This first bulletin seems like it could be the problem because engine movement is involved:

GM Corporate Bulletin 00-06-04-049B
This Bulletin covers a problem that can cause multiple failures, one of which is an Antilock brake problem, and covers 2000-2003 Impala and Monte Carlo built prior to 2/03.
Check to make sure the wiring harness adjacent to the AC accumulator/dryer is not rubbing against the ac accumulator chaffing through the insulation of the wires in the harness.

GM Corporate Bulletin 03-05-25-008 overview:
GM front wheel speed sensor harness replacement - 2001-2003 Buick Century, Regal; 2001-2003 Chevrolet Impala, Monte Carlo; 2001-2002 Oldsmobile Intrigue; 2001-2004 Pontiac Grand Prix
This bulletin is about inspecting the harness going to the front wheel speed sensor for wear from contact with front suspension parts.
Repair harnesses/leads are available that can be spiced onto the main harness.
2001-2003 impala & Monte Carlo – Right side - 10340313
2001-2003 impala & Monte Carlo – Left side - 10340314

SERVICE BRAKES, HYDRAULIC:ANTILOCK:ABS WARNING LIGHT
• TSB #030525008 -- INTERMITTENT/CONSTANT ANTI-LOCK BRAKING SYSTEM (ABS) MALFUNCTION INDICATOR LAMP (MIL) ILLUMINATED. *TT (NHTSA ID #10004719, OCTOBER 01 2003)

Hope helped.

Two items to consider when doing that swap...First, the smaller tires must turn faster to go the same speed/distance as the larger ones which will affect fuel consumption and alter speedometer reading. Second, your abs brake system reads wheel speed and having different turning rates may be interpreted as a partial skid which can cause problems. Best to stay with same size on front and rear.

When you replaced the ABS sensor on the hub, did you clean and re-gap the sensor to the speed ring on the hub. There was a recall on the ABS Malfunction on your truck. The tire size don't make a difference to your ABS as long as all four tires are the size, There was a issue bulletin with your Tahoe on the ABS activating under 8 km/h. Good luck and hope this helps, if not clean out the sensor with brake parts cleaner and check the wire harness and ABS sensor bracket. Re gap the sensor to the speed ring hub. Here is the bulletin. Anti lock Brake (ABS) Activation at Low Speeds (Clean Wheel Speed Sensor Mounting Surface) #03-05-25-007C - (05/16/2006) 2001-2006 Chevrolet Suburban, Tahoe, Silverado

I would pull the fuse for the ABS hydraulic pump and then put it back in and see what happens. Don't ever recall a pump running. Dealer may need to hook up scan tool for diagnostic fault codes, DTCs.



Principles of Operation
The ABS control module receives wheel speed readings from both front wheel speed sensors and the rear differential speed sensor, and processes this information to determine if an ABS event is necessary. The wheel speed sensor electrically senses each tooth of the ABS sensor indicators as it passes through the wheel speed sensor's magnetic field.
The ABS control module continuously monitors and compares the rotational speed of each wheel speed sensor indicator and, when it detects an impending wheel lock, modulates brake pressure to the appropriate brake caliper(s). This is accomplished by triggering the hydraulic control unit (HCU) to open and close the appropriate solenoid valves. Once the affected wheel returns to normal speed, the ABS control module returns the solenoid valves to their normal position, and normal (base) braking resumes.
The ABS control module is self-monitoring. When the ignition switch is turned to the RUN position, the ABS control module will do a preliminary electrical check, and at approximately 20 km/h (12 mph), the pump motor is turned on for approximately one-half second. Any malfunction of the ABS system will cause the ABS to shut off; normal power assisted braking, however, remains.
Inspection and Verification — Scan Tool Communications Check

1. Verify the customer concern by carrying out the Drive Cycle Test.

1. Visually inspect for obvious signs of mechanical and electrical damage.

Visual Inspection Chart Mechanical Electrical

• Parking brake cable
• Tire pressure
• Tire size or mismatched tires

• Blown fuse
• Central junction box (CJB):
  • fuse 23 (10A)
• Battery junction box
  • fuse 102 (50A)
• Connectors or connections
• Ground integrity
• Harness routing
• Wire chafing
• Circuitry open/shorted

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Anti-Lock Control The four-wheel anti-lock brake system (4WABS) consists of the following components:

• Anti-lock brake control module (2C265)
• Front anti-lock brake sensor (2C204)
• Front anti-lock brake sensor indicator (2C182)
• Hydraulic control unit (2C219)
• Rear anti-lock brake sensor (2C190)
• Rear anti-lock brake sensor indicator (2C189)
• Yellow ABS warning indicator

Sounds as if you have a false activation of the ABS system.
If the light does not come on until you are driving then the ABS module is probably seeing a difference in wheel speed from side to side. It could be caused by different size tires,are all your tires the same size and brand? It could be caused by one tire having low tire pressure. It could also be one of the sensor rings esp. on the front has maybe cracked and slipped out of place causing the air gap between the sensor and the ring to be larger than it is suppose to be.The gap between sensor and ring is usually 0.045 of an inch sometimes the ring which is pressed onto the outer CV joint will crack and the ring will slid up the joint slightly away from the sensor.This will decrease the amplitude of the sensor signal and ABS interputs this as a wheel trying to slip or lock up and activates the ABS.When ABS activates it will make a loud pulsing type sound and it will almost feel like it is not going to stop.