How To Repair Kelsey Hayes Abs Module

Habitation, Machine Repair Library, Car Parts, Accessories, Tools, Manuals & Books, Automobile BLOG, Links, Alphabetize

Kelsey-Hayes 4WAL Antilock Brakes

Copyright AA1Car

In 1990, Kelsey-Hayes introduced a new four-wheel anti-lock braking organization (EBC4) on General Motors M- and L-series minivans (Chevrolet Astro and GMC Safari). Full general Motors refers to the organization as 4WAL. The following year 4WAL was offered on the Southward- and T-series trucks (Chevy Blazer, GMC Jimmy iv-door) and the GMC Syclone. In 1992, the four-wheel anti-lock braking organization was added to the two-door Southward- and T-series trucks, Suburban, full-size Blazer/GMC Yukon, Geo Tracker and the limited-production GMC Typhoon.

The 4WAL system is a nonintegral, four-wheel, 3-channel ABS organisation with a conventional master cylinder and brake booster. Each forepart brake circuit is controlled independently, but both rear brakes are controlled every bit a pair. The system also functions in four-bicycle drive, so it is a fulltime system unlike some of the earlier RWAL Rear Wheel Antilock Brake applications where the ABS organisation was deactivated when switching from two- to four-bicycle bulldoze.

On most 4WAL applications, four bicycle speed sensors are used (i for each wheel). On the 1992 Suburban, however, simply the forepart wheels have individual speed sensors. A transmission-mounted vehicle speed sensor provides a mutual indicate for both rear wheels.

The forepart wheel speed sensors on two-wheel-drive trucks are located on the splash shield backside the brake rotor, with the sensor ring behind the rotor. On four-wheel-drive trucks, the front sensors are mounted backside the splash shield and tin can be replaced without having to pull the restriction rotor. The tone ring, however, is part of the cycle bearing associates. Air gaps on both types of front wheel speed sensors are nonadjustable and are factory set at .050 inches.

The rear bike speed sensors are located on the rear brake backing plates with rings pressed onto the ends of the axle shafts. The air gap is nonadjustable.

On all 4WAL applications except the 1992 Suburban, the signals from the bike speed sensors get directly to the electronic control unit (no DRAC module is used). Simply on the Suburban, the speed sensor signal for the rear wheels showtime goes through an electronic "buffer" that's similar to the DRAC module in RWAL applications. The buffer divides up the vehicle speed signal into diverse frequencies that are used by the cruise-control system, engine-command module and electronic speedometer and odometer, as well as the anti-lock brake system.

The ABS command module is mounted on the hydraulic modulator assembly, which Full general Motors calls the Electro-Hydraulic Control Unit (EHCU). One variation is the EBC4-VCM arrangement on 1994 and up Chevy S- and T-series trucks. On these applications, in that location is no ABS command module on the modulator. The ABS control electronics take been integrated into the engine command module then a unmarried module controls both systems.

The ABS control module receives input from the bicycle speed sensors and a restriction pedal switch. On trucks with automatic transmissions, the brake switch circuit contacts likewise control power to the transmission torque converter clutch. The switch is normally airtight, and provides a 12-volt electrical signal to the ABS controller. With the brake pedal applied, the switch opens and supplies less than one volt to the controller.

The 4WAL arrangement too has a 4WD switch and indicator light. The 4WD switch is needed to change the ABS control logic when the vehicle is shifted into iv-wheel drive. The switch is mounted on the front beam in T-serial trucks, and is open up in two-wheel bulldoze, supplying less than one volt to the controller. The switch is closed in four-cycle drive and supplies 12 volts to the controller. The switch is role of the indicator light excursion and is mechanically operated by the shift linkage in the transfer case.

For diagnostic purposes, at that place'due south both a red Restriction and amber ANTI-LOCK alarm lite - instead of the single scarlet BRAKE alarm light that's used on Kelsey-Hayes rear-wheel ABS systems. In that location is also an Assembly Line Diagnostic Link (ALDL) diagnostic connector which tin can exist used for transmission fault code retrieval or diagnosing with a scan tool.

KELSEY-HAYES 4WAL ELECTRO-HYDRAULIC CONTROL UNIT (EHCU)

The EHCU contains half dozen ABS solenoid valves, an isolation valve and a modulation valve for each of the three individual restriction circuits. The EHCU besides has a single pump motor that drives two split up pumps (1 for the front brakes and the other for the rear brakes). The relay for the pump motor is located inside the EHCU. As well inside the EHCU are four pressure level accumulators - ane front and 1 rear depression-pressure accumulator, and ane front and i rear high-pressure accumulator. In that location are also 3 reset switches (ane for each front brake and i for the combined rear brake circuit). The EHCU is located under the chief cylinder in the engine compartment on the Astro and Safari vans, and on the left cycle well on S- and T-series Blazers.

KELSEY-HAYES 4WAL Organization OPERATION
During normal braking, fluid force per unit area from the primary cylinder passes through the normally open isolation and modulation solenoid valves in the EHCU to the individual brakes. Only, when the controller senses that bicycle lockup is about to occur during braking, it activates anti-lock braking.

The EHCU begins ABS operation in the usual way by energizing the ABS isolation solenoid for the affected bicycle to block any further pressure increase to the restriction. At the aforementioned fourth dimension, the pump motor relay is energized to start the pump. This primes the system and builds pressure in the high-pressure accumulator for the pressure increment phase of anti-lock braking. The next step is to energize the filibuster ABS solenoid, which is referred to every bit the Pulse-Width Modulation (PWM) valve, to bleed pressure level from the restriction. The 4WAL control module can vary the amount of pressure decrease by varying the valve'due south open or ON fourth dimension. It does this by varying the ON time or duration of the voltage to the solenoid.

When the PWM valve is energized and closes, it opens a passage that allows pressure to be released from the brake circuit. The force per unit area is dumped into one of the two low-pressure accumulators. The spring-loaded low-pressure accumulator (LPA) serves as a temporary storage reservoir to hold the fluid until information technology can exist rerouted back into the arrangement. It also maintains sufficient fluid pressure in the EHCU to keep the high-force per unit area pump primed.

As pressure is reduced in the brake circuit that's being controlled, the reset switch for that circuit may trip signaling the ABS command module that fluid pressure has dropped to the bespeak where additional force per unit area is needed to maintain proper braking activeness. At this point, the command module will de-energize the PWM valve and initiate the pressure increment mode.

When the PWM reopens, fluid pressure from the loftier-pressure level accumulator (HPA) and high-pressure pump enters the brake excursion and builds brake pressure. This reapplies the brake as the cycle continues to decelerate. This reset switch also returns to its normal position equally pressure level is restored. The ABS controller so continues to cycle the PWM valve every bit needed to forestall bike lockup for the elapsing of the stop.

During the pressure hold, subtract and increment phases of anti-lock braking, the isolation valve for the brake excursion remains airtight. This blocks brake pressure level from the main cylinder and so it tin can't enter the brake circuit beingness controlled. The reapplication of brake pressure level, therefore, must come from the high-pressure pump and accumulator.

One time the need for ABS braking has passed, the isolation and PWM valves are de-energized and normal braking is restored. The residual pressure that remains in the high-force per unit area accumulator is bled off into the main cylinder reservoir and the system returns to the passive way until it is needed again.

KELSEY-HAYES 4WAL ANTILOCK Restriction DIAGNOSTICS

The self-diagnostic capabilities of the 4WAL system are much better than the earlier RWAL or RABS system, and include more than fault codes and the ability to log and display multiple codes. The controller monitors all system inputs while driving, and performs an automatic self-examination every time the vehicle is started and driven faster than eight mph. Initial self-checks can reveal bug such as opens or shorts in the cycle speed sensors, internal bug in the electronic controller, and problems in the ABS and brake light warning circuits.

The self-diagnostics will too cheque for abnormal bicycle speed sensor readings at speeds to a higher place three mph. When the vehicle reaches 8 mph, the controller cycles the solenoids, relays and pump motor to cheque their operation. The auto test may be heard and felt past the commuter while it is taking identify, but does non indicate a problem. If the brake pedal is depressed (or the switch is open), the organization will not perform the cocky-exam until the pedal is released.

The controller will illuminate the amber ABS alert light when a mistake is detected, log a code and disable the ABS organization. The ABS light will remain on equally long as the fundamental is on, and volition come on again the next fourth dimension the engine is started if the problem still exists. If the problem is intermittent, the warning light will not come dorsum on until the problem repeats unless information technology is a "hard" (latching) code. A hard code will keep the ABS warning low-cal on until the code is cleared from memory.

If a mistake occurs in the ABS warning-light circuit, the red brake warning light will come on to alert the driver to ABS problems. The brake warning lite will besides come on if at that place is a hydraulic failure in either brake circuit.

KELSEY-HAYES 4WAL SYSTEM PRECHECKS

Prior to checking the organisation for fault codes, the vehicle should be given a preliminary visual inspection to cheque for obvious problems:

• Ostend whether or non the bister ABS and/or red restriction warning lamps are withal on past doing a bulb check and then starting the engine. If the lamp remains on, the organization has an ABS fault code and requires further diagnosis.
  If the lamp goes out, either no faults have been detected, or the error is intermittent or a soft (non-latching) fault.
• If the restriction and ABS alarm lamps neglect to illuminate when the cardinal is turned on, check all arrangement fuses including the ones for the instrument cluster.
• Check the brake warning light by turning the key on and applying the parking brake. The calorie-free should come on. It should and so get out when the brake is released.
• Cheque the wiring harness connectors on the modulator.
• Check the level of the brake fluid.

KELSEY-HAYES 4WAL ANTILOCK Brake TROUBLE CODES

The 4WAL system provides manual wink codes, and tin also be accessed with a scan tool. Here's the manual procedure.

ane. Connect a jumper wire between pin "A" and pin "H" on the diagnostic connector under the instrument panel (or ground pin "H"), and turn the ignition on. This puts the system into the cocky-diagnostic mode.

two. Codes are displayed by flashes of the ABS warning light. Count the flashes to determine the code number. If the ABS warning light circuit is defective, the codes will exist flashed out past the restriction warning lite.

The first series of flashes will represent the first digit of the fault code. The second serial of short flashes that follow a brief interruption represent the 2nd digit of the code. A lawmaking 12, for instance, would appear as a wink, break, flash, flash.

One of the codes received will exist a normal system code: code 12 with the restriction not applied in the 2WD manner; lawmaking thirteen with brake practical in 2WD mode; code 14 with restriction not practical in 4WD fashion; or code 15 with brake applied in 4WD mode. This normal code allows the restriction and 4WD switches to be tested without having to use a browse tool.

Each code will repeat three times earlier the next code is displayed.

To erase stored fault codes, a scan tool or the following manual procedure can be used.

one. Turn the ignition switch on.

2. Connect a jumper wire or key between diagnostic connector terminals "H" and "A" (or footing "H") - and wait two seconds.

three. Remove the jumper wire for one 2nd.

4. Repeat the grounding for two more seconds. The ABS warning lite should go out if the codes have been successfully erased.

This process is necessary only on certain difficult codes. Soft codes can be cleared past correcting the system problem and turning the ignition off for approximately five seconds.

KELSAY-HAYES 4WAL SCAN TOOL DIAGNOSIS

The Kelsey-Hayes 4WAL ABS system can also be diagnosed with a browse tool. Yet, a bi-directional scan tool with the advisable software is necessary to read history codes and to perform diverse tests. These include:

• Check voltages at the diagnostic connector terminal "H."
• Wheel speed sensor output (in miles-per-hour) from each sensor.
• Reset switch status (right front end, left forepart and rear).
• Function tests of the hydraulic modulator.
• Capture "snapshot" data during a test bulldoze for later analysis.

History codes in the 4WAL system reveal the number of ignition bulldoze cycles since a error occurred. A drive cycle is defined as the vehicle existence started and driven above a specified speed, usually about eight mph with the 4WAL system.

KELSAY-HAYES RWAL Depression PEDAL Trouble

A pedal that gradually sinks to the floor commonly indicates a worn main cylinder. But on Kelsey-Hayes rear-wheel ABS applications, the condition may exist caused past clay in the ABS modulator valve. Dirt tin can prevent the dump valve from fully seating and allow rear brake force per unit area to leak past the valve.

To isolate the problem, disconnect the steel brake line from the principal cylinder that supplies the rear brakes. And then take a helper depress the brake pedal about an inch to purge air from the outlet port. Install a tube plug in the port and tighten it, making certain pedal pressure is maintained to preclude damage to the primary cup every bit it moves across the vent port in the master cylinder. If the pedal continues to sink subsequently the plug is installed, the master cylinder is leaking and needs to be replaced. If the pedal holds firm, however, then the problem is in either rear brake circuit or the ABS control valve. To pinpoint the problem, block off the outlet port at the ABS control valve and recheck pedal feel every bit earlier. If the pedal now feels hard, the trouble is probably a leaky rear wheel cylinder. But if the pedal continues to sink, the ABS dump valve is leaking and the ABS control valve assembly needs to exist replaced.

KELSEY-HAYES 4WAL BLEEDING PROCEDURE

Brakes can exist bled in the usual way manually or with pressure level or vacuum equipment. The wheel bleeding sequence is RR, LR, RF, LF. If a pressure bleeder is used, the combination valve must be held open.

If the EHCU Modulator or accumulator accept been replaced, or air has entered the ABS role of the system, the EHCU modulator volition have to be bled using i of two special procedures:

The preferred method is to cycle the ABS system using a manufactory scan tool or an aftermarket pro-level browse tool that has bi-directional capabilities and then it can access the ABS arrangement and cycle the pump and solenoids. A basic DIY scan tool that simply reads codes and sensor data cannot practice this.

If you tin't get your hands on the proper browse tool, you lot tin employ the post-obit manual bleeding procedure:

1. First, bleed the entire brake system using a force per unit area bleeder or vacuum bleeder. Pumping the brake pedal also works simply must be done advisedly and then air doesn't siphon back into the lines. Bleed the wheels in this social club: Right Rear, Left Rear, Right Forepart, Left Front end.

2. Once all the air is out of the master cylinder and brake lines (no bubbles in the clear plastic bleeder hose yous have attached to each of the calipers or wheel cylinders), yous tin can proceed to haemorrhage the ABS system.

three. Open the internal bleed screws on the modulator one quarter to a half-turn. These are the cap screws on either side of the modulator. Annotation: Some newer 4WAL systems practice Non have these bleed screws and then yous must employ a scan tool to bleed the organisation or try loosening the brake lines to the modulator to vent air.

4. Connect special tools (such as Kent-Moore No. J39177) to concord open the high-pressure accumulator bleed valves.

5. Open the two bleeder screws at the BPMV and bleed the unit by forcing fluid through it with a pressure bleeder or by slowly pumping the restriction pedal. Do Not let the master cylinder reservoir to run low (add brake fluid equally needed during this procedure).

vi. Bleed the wheels again as before: RR, LR, RF, LF

7. Tighten the modulator bleed screws and remove the tools from the high-pressure accumulators.

8. Plow the ignition on and start the engine. Press down firmly on the restriction pedal several times. If the pedal does not feel firm, turn the engine off, pump the pedal to save remainder pressure level in the system, and drain each of the four brakes every bit before to get rid of whatsoever air in the system.

Information technology's a pain to go through all of these steps, but if you practise not and air is trapped in the ABS unit of measurement (or pump on applications that have a pump), information technology volition eventually get into the lines and requite y'all a soft pedal.

---

Related Antilock Brake Manufactures

Antilock Restriction Systems

ABS System Application Nautical chart (by vehicle year, brand & model)

Antilock Braking Systems (1998 model yr)

ABS Systems Come Under Fire

New ABS Diagnostic Testers

Pulling ABS Diagnostic Codes

Diagnosing ABS Wheel Speed Sensors

Honda Antilock Brakes

Chrysler Dodge Plymouth Minivan Bendix ten Antilock Brakes

GM Delphi DBC-7 ABS Antilock Brakes

Jeep Bendix ix Antilock Brakes

Kelsey-Hayes RWAL Rear Wheel Antilock Brakes

Teves Marker 20 Antilock Brakes

Electronic Stability Control

Restriction-By-Wire

Antilock Brake Guide product information

GM SUV Call up for ABS problem (August 2005)

Fixes For Common Brake Issues

Click Here to Meet More Carley Automotive Technical Articles

Click Here for Quick Reference Guide to Antilock Brakes

Click Hither for Brake Repair Guide

---

Be sure to visit our other websites:

Machine Repair Yourself

Carley Automotive Software

OBD2HELP

Random-Misfire

ScanToolHelp

TROUBLE-CODES

Source: https://www.aa1car.com/library/abs_kelseyhayes.htm

Share this post