Hey Guys,

My truck is doing some weird stuff today.

The ABS and Brake light are lit up on the dash now but still seem to be working fine. No leaks or anything there so it must be a technical issue?

Also, the Speedometer needle tends to "wobble" back and forth lots while i am at a steady highway speed.

The speedometer also "wobbles" from 0 to 30 kph when I push the brake in to put it in any gear. (its an automatic.)

Thanks in advance for any advice/suggestions.

 

SENSOR- WHEEL SPEED-ABS-FRONT


DESCRIPTION



The ABS brake system uses 3 wheel speed sensors. A sensor is mounted to each front hub/bearings. The third

sensor is mounted on top of the rear axle differential housing.


OPERATION



The Wheel Speed Sensor consists of a magnet (1)

surrounded by windings from a single strand of wire

(5). The sensor sends a small AC signal to the ABM.

This signal is generated by magnetic induction. The

magnetic induction is created when a toothed sensor

ring (exciter ring or tone wheel) (4) passes the stationary

magnetic WSS.

When the ring gear is rotated, the exciter ring (4)

passes the tip of the WSS. As the exciter ring tooth

approaches the tip of the WSS, the magnetic lines of

force expand, causing the magnetic field to cut across

the sensor’s windings (5). This, in turn causes current

to flow through the WSS circuit in one direction. When

the exciter ring tooth moves away from the sensor tip,

the magnetic lines of force collapse cutting the winding

in the opposite direction. This causes the current

to flow in the opposite direction. Every time a tooth of


DR/DH BRAKES - ABS - SERVICE INFORMATION 5 - 289

the exciter ring passes the tip of the WSS, an AC signal is generated current. Each AC signal (positive to negative

signal or squarewave) is interpreted by the ABM. It then compares the frequency of the sinewave to a time value to

calculate vehicle speed. The ABM continues to monitor the frequency to determine a deceleration rate that would

indicate a possible wheel-locking tendency.

The signal strength of any magnetic induction sensor is directly affected by:


² Magnetic field strength; the stronger the magnetic field, the stronger the signal

² Number of windings in the sensor; more windings provide a stronger signal

² Exciter ring speed; the faster the exciter ring/tone wheel rotates, the stronger the signal will be

² Distance (3) “air gap” between the exciter ring teeth and WSS; the closer the WSS is to the exciter ring/tone



wheel, the stronger the signal will be.

The WSS is not adjustable. A clearance specification has been established for manufacturing tolerances. If the

clearance is not within these specifications, then either the WSS or other components may be damaged. The clearance

between the WSS and the exciter ring is 0.005 – 0.050 in.

The assembly plant performs a “Rolls Test” on every vehicle that leaves the assembly plant. One of the test performed

is a test of the WSS. To properly test the sensor, the assembly plant connects test equipment to the Data

Link Connector (DLC). This connector is located to the right of the steering column and attached to the lower portion

of the instrument panel. The rolls test terminal is spliced to the WSS circuit. The vehicle is then driven on a set of

rollers and the WSS output is monitored for proper operation.


REMOVAL



1. Remove the front rotor (Refer to 5 - BRAKES/HYDRAULIC/

MECHANICAL/ROTORS - REMOVAL).

2. Remove the wheel speed sensor mounting bolt (1)

from the hub (3).

3. Remove the wheel speed sensor (2) from the hub

(3).

4. Remove the wiring from the clips and disconnect

the electrical connector.


5 - 290 BRAKES - ABS - SERVICE INFORMATION DR/DH



INSTALLATION



1. Install the wiring to the clips and Reconnect the

electrical connector.

2. Install the wheel speed sensor (2) to the hub (3).

3. Install the wheel speed sensor mounting bolt (1) to

the hub (3). Tighten the bolt to 21 N·m (190 in.

lbs.).

4. Install the front rotor and brake caliper assembly

(Refer to 5 - BRAKES/HYDRAULIC/MECHANICAL/

ROTORS - INSTALLATION).


SENSOR-WHEEL SPEED-ABS-REAR


DIAGNOSIS AND TESTING

REAR WHEEL ANTILOCK



Diagnosis of base brake conditions which are mechanical in nature should be performed first. This includes brake

noise, lack of power assist, parking brake, or vehicle vibration during normal braking.

The RWAL brake system performs several self-tests every time the ignition switch is turned on and the vehicle is

driven. The CAB monitors the system inputs and outputs circuits to verify the system is operating properly. If the

CAB senses a malfunction in the system it will set a DTC into memory and trigger the warning lamp.


NOTE: The MDS or DRB III scan tool is used to diagnose the RWAL system. For test procedures refer to the

Chassis Diagnostic Manual.


REMOVAL



1. Raise the vehicle on a hoist.

2. Remove the brake line mounting nut and remove

the brake line from the sensor stud.

3. Remove the mounting stud (2) from the sensor and

shield.

4. Remove the sensor (1) and shield from the differential

housing (3).

5. Disconnect the sensor wire harness and remove

the sensor (1).


DR/DH BRAKES - ABS - SERVICE INFORMATION 5 - 291



INSTALLATION



1. Connect the harness to the sensor. Be sure the




seal is securely in place between the sensor

and the wiring connector.



2. Install the O-ring on the sensor (if removed).

3. Insert the sensor (1) in the differential housing (3).

4. Install the sensor shield.

5. Install the sensor mounting stud (2) and tighten to

24 N·m (200 in. lbs.).

6. Install the brake line on the sensor stud (2)and

install the nut.

7. Lower the vehicle.


WHEEL-TONE


DIAGNOSIS AND TESTING

REAR WHEEL SPEED SENSOR



Diagnosis of base brake conditions which are mechanical in nature should be performed first. This includes brake

noise, lack of power assist, parking brake, or vehicle vibration during normal braking.

The Antilock brake system performs several self-tests every time the ignition switch is turned on and the vehicle is

driven. The CAB monitors the system inputs and outputs circuits to verify the system is operating properly. If the

CAB senses a malfunction in the system it will set a DTC into memory and trigger the warning lamp.


NOTE: The MDS or DRB III scan tool is used to diagnose the Antilock Brake system. For test procedures

refer to the Chassis Diagnostic Manual.

 

I think I would start by checking all the connections for the wheel sensors front and back, If I would hedge a guess, I would guess something going on with the rear, but as you can see from the text, their all interrelated

 

Hm.. Could be the gauge cluster. My buddy's truck did the same thing. I'm betting that is what is happening with your truck. My buddy had to get a whole new gauge cluster. Good luck.

 

Thanks for the help guys. I will look at those sensors when I get off work later.