1994 Chrysler LHS Repair Question
1994 Chrysler LHS brakes applying themselves
1994 Chrysler LHS 6 cyl Front Wheel Drive Automatic 119000 miles
my brakes seemed to be sticking.i noticed a big power loss like a clogged cadilac conv. or as if i was pulling a trailer. After paying a little bit closer attention to the details i noticed that my brakes are applying by itself noticably when i press the accelerator.It only does it sometimes,generally after runing a while.The Cadillac conv. checked out at a shop.Theres no check engine light but my Air bag light did come on.Pulled fuses to ABS and problem still persisted.Ive had 3 mechanics check it out and all thought i was crazy cause there was no problem when they checked it out.Is it A short?Please help
Tell them to check for fault messages and also see below
NOTE:For more information on brake system, see BRAKE SYSTEM article in the BRAKES section.
The Teves-Mark IV Anti-Lock Brake System (ABS) and Low-Speed Traction Control System (LTCS) are designed to prevent wheel lock-up during heavy braking and acceleration slip at speeds less than 30 MPH. ABS allows driver to maintain steering control while stopping vehicle in shortest distance possible. LTCS allows fast acceleration control, minimizing wheel-spin.
Major ABS components include Controller Anti-lock Brake (CAB), brake boost/master cylinder assembly with integrated Pedal Travel Sensor (PTS), Hydraulic Control Unit (HCU), pump/motor assembly, 2 proportioning valves, 4 wheel speed sensor/tone wheel assemblies, ABS relay, pump/motor relay, BRAKE warning light (Red), ANTI-LOCK warning light (Amber), and 2 fluid reservoirs with separate fluid level switches. See Fig. 1.
All models equipped with LTCS use ABS components to control wheel spin by applying brakes to slipping wheel. Major LTCS components also include traction control function switch, traction control warning light (Amber), and traction control active light (Green).
Fig. 1: Locating ABS Components
Courtesy of CHRYSLER CORP.
During normal driving and braking operations, ABS acts like a conventional braking system. Each Wheel Speed Sensor (WSS) constantly sends an AC voltage signal to the Controller Anti-Lock Brake (CAB), which then translates this information into wheel speed.
When CAB determines that wheel(s) are about to lock-up or slip, it activates appropriate valve in Hydraulic Control Unit (HCU) to increase or decrease hydraulic pressure to each wheel. A slight pulsation may be felt through brake pedal.
BRAKE, ANTI-LOCK and TRACTION CONTROL warning lights (if equipped) should come on when ignition is turned on and vehicle is started. If any instrument panel warning light stays on longer than about 5 seconds after vehicle is started, system malfunction is indicated. See DIAGNOSIS & TESTING.
PEDAL FEEL CHARACTERISTICS
During ABS stopping or LTCS acceleration, solenoid valve clicking and pump motor operation may be heard and brake pedal vibration/pulsation may be felt. During ABS/LTCS operation, the master cylinder is isolated from wheel brakes, producing a hard pedal feel. A slight brake pedal drop may be felt when ABS/LTCS is shut off.
The system may detect wheel lock-up or slip and activate ABS/LTCS under the following conditions: braking or accelerating on bumpy surface or when sand, gravel or other loose debris is on the road. Under such conditions, hard pedal feel and loss of deceleration/acceleration may be experienced.
Hard pedal feel will not make warning lights come on or set fault message. When investigating a hard pedal feel or excessive system noise, inspect sensor and tone wheel teeth for chips, damaged sensor pole tips, and excessive tone wheel runout or gap.
BLEEDING BRAKE SYSTEM
NOTE:During bleeding procedure, ensure fluid level remains close to full. Check fluid level periodically while bleeding system. Add DOT 3 brake fluid as required.
Teves-Mark IV ABS system must be bled as 2 independent braking systems. Always bleed base brake system using manual bleeding or pressure bleeding procedure before bleeding Hydraulic Control Unit (HCU). See MANUAL BLEEDING or PRESSURE BLEEDING. HCU must be bled separately. See BLEEDING HYDRAULIC CONTROL UNIT. Bleeding HCU requires Diagnostic Readout Box (DRB). Always repeat base system bleeding procedure after bleeding HCU.
Fill master cylinder. Install clear vinyl bleed hose onto right rear bleed valve. Place other end of hose in clean transparent container. Partially fill container with clean brake fluid. Submerge end of hose in fluid.
Pump brake pedal 3-4 times. Hold brake pedal down. Open bleed valve 1-2 turns. Slowly depress brake pedal through its full travel. Close bleed valve. Release pedal. Repeat procedure until flow of brake fluid is clear and free of bubbles. Proceed to next bleed valve of brake bleeding sequence. See BRAKELINE BLEEDING SEQUENCE table.
BRAKELINE BLEEDING SEQUENCE
All ModelsRR, LR, RF, LF
Clean master cylinder cap and surrounding area. Remove cap. With pressure tank at least half full, connect tank to master cylinder using appropriate adapters.
Attach bleed hose to right rear bleed valve. Place other end of hose in clean transparent container. Partially fill container with clean brake fluid. Submerge end of hose in fluid.
Open release valve on pressure bleeder. Open bleed valve 1-2 turns, noting fluid flow. When flow is clear and free of bubbles, close bleed valve securely.
Repeat procedure for remaining bleed valves in appropriate sequence. See BRAKELINE BLEEDING SEQUENCE table. Close release valve on pressure bleeder. Remove pressure tank from master cylinder. Check fluid level of master cylinder reservoir.
BLEEDING HYDRAULIC CONTROL UNIT
WARNING:Ensure manual or pressure bleeding procedure is performed before bleeding Hydraulic Control Unit (HCU).
Bleed base brake system using standard manual or pressure bleeding procedures. See MANUAL BLEEDING or PRESSURE BLEEDING. Connect DRB to Blue 6-pin Chrysler Collision Detection (CCD) data link connector, located under lower dash panel, right of steering column. See Fig. 2.
Using DRB, select TEVES ABS MENU. Select ADJUSTMENTS. Ensure parking brake is set. Select BLEED BRAKES. DRB will display following in sequence: BLEED BRAKES ACTUATING MOTOR PUMP, BLEED BRAKES ACTUATING ALL OUTLET VALVES & MOTOR PUMP, BLEED BRAKES ACTUATING MOTOR PUMP, and BLEED BRAKES COMPLETE. After BLEED BRAKES COMPLETE is displayed, disconnect DRB. Repeat standard bleeding procedure.
Fig. 2: Locating CCD Data Link Connector
Courtesy of CHRYSLER CORP.
DIAGNOSIS & TESTING
Teves-Mark IV Anti-Lock Brake System (ABS) is controlled and monitored by Controller Anti-Lock Brake (CAB). In addition to controlling ABS system, CAB has several useful diagnostic capabilities.
Fault messages are stored in memory until erased by a technician using Chrysler's Diagnostic Readout Box (DRB) or until erased automatically after 50 ignition cycles. Only fault which cannot be erased using DRB or after 50 ignition cycles is a CAB fault. CAB fault can only be erased by replacing CAB.
More than one fault message can be stored at a time. Number of fault messages stored is displayed by DRB. Number of ignition cycles since most recent fault was stored is also displayed.
Using DRB, most functions of CAB and ABS system can be accessed by technician for testing and diagnostic purposes.
Start-up cycle is an electrical check of ABS system and anti-lock light relays, and takes place immediately after ignition is turned on. During this check, ANTI-LOCK light in instrument cluster comes on and then goes out at completion of start-up cycle test. Test cycle lasts 1-2 seconds.
Drive-off cycle takes place first time vehicle reaches about 3 MPH after an ignition reset.
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