1993 VOLKSWAGEN CORRADO Repair Manual

ANTI-LOCK BRAKE SAFETY PRECAUTIONS
Article Text
1993 Volkswagen Corrado
For Volkswagen Technical Site: http://vw.belcom.ru
Copyright © 1998 Mitchell Repair Information Company, LLC
Wednesday, March 22, 2000 08:57PM
ARTICLE BEGINNING
GENERAL INFORMATION
Anti-Lock Brake Safety Precautions
* PLEASE READ THIS FIRST *
This article is intended for general information purposes
only. This information may not apply to all makes and models. If
vehicle is equipped with Anti-Lock Brake System (ABS), refer to
appropriate ANTI-LOCK BRAKE SYSTEM article in the BRAKES section for
description, operation, depressurizing, testing, system bleeding,
trouble shooting and servicing of specific system.
WARNING: Failure to depressurize ABS could lead to physical injury.
ANTI-LOCK BRAKE SAFETY PRECAUTIONS
WARNING: Failure to depressurize ABS could lead to physical injury.
* NEVER open a bleeder valve or loosen a hydraulic line
while ABS is pressurized.
* NEVER disconnect or reconnect any electrical connectors
while ignition is on. Damage to ABS control unit may result.
* DO NOT attempt to bleed hyudarulic system without first
referring to the appropriate ANTI-LOCK BRAKE SYSTEM article
in the BRAKES section.
* Only use specially designed brake hoses/lines on ABS equipped
vehicles.
* DO NOT tap on speed sensor components (sensor, sensor rings).
Sensor rings must be pressed into hubs, NOT hammered into
hubs. Striking these components can cause demagnetization or
a loss of polarization, affecting the accuracy of the speed
signal returning to the ABS control unit.
* DO NOT mix tire sizes. Increasing the width, as long as tires
remain close to the original diameter, is acceptable. Rolling
diameter must be identical for all 4 tires. Some
manufacturers recommend tires of the same brand, style and
type. Failure to follow this precaution may cause inaccurate
wheel speed readings.
* DO NOT contaminate speed sensor components with grease. Only
use recommended coating, when system calls for an
anti-corrosion coating.
* When speed sensor components have been removed, ALWAYS check
sensor-to-ring air gaps when applicable. These specifications
can be found in each appropriate article.
* ONLY use rocommended brake fluids. DO NOT use silicone brake
fluids in an ABS equipped vehicle.
* When instlling transmittion devices (CB's, telephones, etc.)
on ABS equipped vehicles, DO NOT locate the antenna near the
ABS control unit (or any control unit).

ANTI-LOCK BRAKE SAFETY PRECAUTIONS
Article Text (p. 2)
1993 Volkswagen Corrado
For Volkswagen Technical Site: http://vw.belcom.ru
Copyright © 1998 Mitchell Repair Information Company, LLC
Wednesday, March 22, 2000 08:57PM
* Disconnect all on-board computers, when using electric
welding equipment.
* DO NOT expose the ABS control unit to prolonged periods of
high heat (185 øF/85øC for 2 hours is generally considered a
maximum limit).
END OF ARTICLE

ANTI-LOCK BRAKE SYSTEM
Article Text
1993 Volkswagen Corrado
For Volkswagen Technical Site: http://vw.belcom.ru
Copyright © 1998 Mitchell Repair Information Company, LLC
Wednesday, March 22, 2000 08:57PM
ARTICLE BEGINNING
1993 BRAKES
Volkswagen Anti-Lock
Corrado SLC
ANTI-LOCK BRAKE SAFETY PRECAUTIONS
* NEVER open a bleeder valve or loosen a hydraulic line while
ABS is pressurized
* NEVER disconnect or reconnect any electrical connectors while
ignition is on. Damage to ABS control unit may result.
* DO NOT attempt to bleed hydraulic system without first
referring to the appropriate article.
* Only use specially designed brake hoses/lines on ABS-equipped
vehicles.
* DO NOT tap on speed sensor components (sensor, sensor rings).
Speed rings must be pressed, NOT hammered into hubs. Striking
these components can cause demagnetization or a loss of
polarization, affecting the accuracy of the speed signal
returning to the ABS control unit.
* DO NOT mix tire sizes. Increasing the width, as long as tires
remain close to the original diameter, is acceptable. Rolling
diameter must be identical for all 4 tires. Some
manufacturers recommend tires of the same brand, style and
type. Failure to follow this precaution may cause inaccurate
wheel speed readings.
* DO NOT contaminate speed sensor components with grease. Only
use recommended anti-corrosion coating.
* When speed sensor components have been removed, ALWAYS check
sensor-to-ring air gaps when applicable. These specifications
can be found in each appropriate article.
* ONLY use recommended brake fluids. DO NOT use silicone brake
fluids in an ABS-equipped vehicle.
* When installing transmitting devices (CB's, telephones, etc.)
on ABS-equipped vehicles, DO NOT locate the antenna near the
ABS control unit (or any control unit).
* Disconnect all on-board computers, when using electric
welding equipment.
* DO NOT expose the ABS control unit to prolonged periods of
high heat (185øF/85øC for 2 hours is generally considered a
maximum limit).
DESCRIPTION
A Teves Anti-Lock Brake System (ABS) is used. See Fig. 1.
This system reduces the chance of wheel lock-up during heavy braking.
The system consists of 4 wheel speed sensors, Electronic Control Unit
(ECU), hydraulic modulator/pump and solenoid valves, ANTILOCK and
BRAKE warning lights. There are 2 relays located at fuse/relay panel,

ANTI-LOCK BRAKE SYSTEM
Article Text (p. 2)
1993 Volkswagen Corrado
For Volkswagen Technical Site: http://vw.belcom.ru
Copyright © 1998 Mitchell Repair Information Company, LLC
Wednesday, March 22, 2000 08:57PM
to protect the hydraulic modulator and ECU.
NOTE: For more brake system information, see BRAKE SYSTEM
article in the BRAKES section.
OPERATION
When pressure is applied to brake pedal, ECU monitors input
signals from each wheel speed sensor. If ECU measures a rate of
reduction greater than what is programmed in ECU, the ECU will output
a signal to appropriate solenoid valve. Each solenoid valve allows
hydraulic pressure to increase or decrease to the appropriate wheel
cylinder.
If a system failure occurs, ANTILOCK warning light, located
on instrument panel, will come on. System will be deactivated, but
conventional brake system will still operate. If brake fluid level
drops too low, BRAKE warning light, located on instrument panel, will
come on.
CAUTION: See ANTI-LOCK BRAKE SAFETY PRECAUTIONS in this article.
CAUTION: The ABS system is under extremely high pressure. Depressurize
the brake system before loosening or removing any hydraulic
component.
DEPRESSURIZING BRAKE SYSTEM
Turn ignition off. Depress and release brake pedal 25-35
times, or until there is a noticeable increase in the effort to
depress the brake pedal. DO NOT turn ignition on until all hydraulic
lines and components are fully tighten.
BLEEDING BRAKE SYSTEM
FRONT BRAKES
Depressurize brake system. See DEPRESSURIZING BRAKE SYSTEM.
Connect a container with hose to left front bleeder screw. Have
assistant depress and release brake pedal a few times. Holding brake
pedal down, open bleeder screw and allow fluid to enter container.
Close bleeder screw and then release brake pedal. Continue this method
until no air is present in fluid. Check master cylinder fluid level to
make sure it does not go below minimum level mark. Use same procedure
for right front brake.
REAR BRAKES
CAUTION: When bleeding rear brakes, accumulator pressure (about 3100
psi) is used to assist in procedure. Use eye protection when
performing this procedure. DO NOT allow pump to run longer
than 2 minutes. See ANTI-LOCK BRAKE SAFETY PRECAUTIONS in

ANTI-LOCK BRAKE SYSTEM
Article Text (p. 3)
1993 Volkswagen Corrado
For Volkswagen Technical Site: http://vw.belcom.ru
Copyright © 1998 Mitchell Repair Information Company, LLC
Wednesday, March 22, 2000 08:57PM
this article.
Attach hose and container to right rear bleeder screw.
Position actuator lever on load-sensing pressure regulator toward rear
of vehicle. Depress brake pedal and turn ignition on. Open bleeder
screw and allow fluid to exit until no air is present in fluid. Close
bleeder screw. Turn ignition off and release brake pedal. Perform same
procedure for left rear brake. Ensure fluid level does not go below
minimum level mark.Fig. 1: Locating ABS Components
Courtesy of Volkswagen United States, Inc.
ADJUSTMENTS
PARKING BRAKE
Raise vehicle and support securely. Release parking brake
lever. Apply brake pedal once. Loosen lock nuts. Tighten each
adjusting nut until lever on respective caliper lifts off stop.
Measure gap between stop and lever. Do not move lever off stop more
than .040" (1 mm). Tighten lock nuts. Ensure wheels lock at 3 notches.
NOTE: No other information on adjustments is available from
manufacturer.
TROUBLE SHOOTING

ANTI-LOCK BRAKE SYSTEM
Article Text (p. 4)
1993 Volkswagen Corrado
For Volkswagen Technical Site: http://vw.belcom.ru
Copyright © 1998 Mitchell Repair Information Company, LLC
Wednesday, March 22, 2000 08:57PM
HYDRAULIC MODULATOR/PUMP
Depressurize brake system. See DEPRESSURIZING BRAKE SYSTEM.
Turn ignition on. Hydraulic modulator/pump should operate for 60
seconds maximum and then stop. Depress brake pedal a few times; pump
should operate again for a few seconds. If pump motor does not
operate, check electrical system. If pump motor operates for more than
60 seconds, internal or external hydraulic leak may be indicated.
Check for external leaks. If external leak is not found, further
testing may be needed to check for internal leaks.
ANTILOCK WARNING LIGHT
Start engine. ANTILOCK warning light should come on, then
turn off after a few seconds. If light does not come on when engine is
started, check electrical system. If light comes on and stays on,
fault has been detected by the ECU and testing will be needed. See
SYSTEM TESTING under DIAGNOSIS & TESTING.
DIAGNOSIS & TESTING
SYSTEM TESTING
NOTE: Check battery condition, brake fluid level, electrical
connections and wiring for damage. If fluid level is
incorrect or battery and/or electrical connections are
faulty, correct problem before preceding. Perform each step,
in sequence, to test entire system, except for ECU. If
faulty ECU is suspected, replace with a known good one, and
retest system. Unplug ECU connector for all test steps.
Power-To-ECU Test
Turn ignition off. Unplug ECU connector. Turn ignition on.
Using a voltmeter, check voltage between ECU connector terminals No. 1
and 2. See Fig. 2. If voltage is 10 volts or more, go to next test. If
voltage is less than 10 volts, check battery, ground, ABS fuse, relay
and wiring. Repair as necessary.Fig. 2: Identifying ECU Connector Terminals
Courtesy of Volkswagen United States, Inc.
ECU Relay Voltage Test
Connect a jumper wire between ECU connector terminals No. 2
and 8. See Fig. 2. Turn ignition on. Using a voltmeter, check voltage
between ECU connector terminals No. 1 and 3. If voltage is 10 volts or
more, go to next test. If voltage is less than 10 volts, check ABS

ANTI-LOCK BRAKE SYSTEM
Article Text (p. 5)
1993 Volkswagen Corrado
For Volkswagen Technical Site: http://vw.belcom.ru
Copyright © 1998 Mitchell Repair Information Company, LLC
Wednesday, March 22, 2000 08:57PM
fuse. If fuse is faulty, replace and retest. If fuse is okay, check
wiring. If wiring is faulty, repair and retest. If wiring is okay,
replace relay and retest.
Brakelight Switch
Turn ignition on. Apply brakes. Check for 12 volts between
terminals No. 12 and 1. If 12 volts are present, brakelight switch is
okay. If 12 volts are not present, check fuse, brakelight switch and
Black/Red wire from brakelight switch to ECU.
Hydraulic Modulator/Pump Relay Voltage Test
1) Turn ignition off. Unplug hydraulic modulator/pump
connector. Depress brake pedal 25 times. Turn ignition on. Using a
voltmeter, measure voltage between ECU connector terminals No. 1 and
32. See Fig. 2. If voltage is 10 volts or more, go to RIGHT REAR WHEEL
SPEED SENSOR VOLTAGE TEST under SYSTEM TESTING.
2) If voltage is less than 10 volts, check hydraulic
modulator/pump fuse. If fuse is okay, check wiring between ECU
connector terminal No. 32 and hydraulic modulator/pump connector
terminal No. 1 (large gauge Red/Black wire). See Figs. 2 and 4. If
wiring is not okay, repair wiring, and retest. If wiring is okay,
replace relay, and retest.
Right Rear Wheel Speed Sensor Voltage Test
Connect an AC voltmeter between ECU connector terminals No. 4
and 22. See Fig. 2. Rotate right rear wheel at one revolution per
second. Measure voltage with wheel rotating. If voltage is 0.075 volt
or more, go to next test. If voltage is less than 0.075 volt, check
wheel speed sensor and/or toothed ring for damage, wear and proper
installation. If damage or wear is found, replace faulty component and
retest. If components are not properly installed, reposition and
retest. If components are okay, replace wheel speed sensor and retest.
Left Rear Wheel Speed Sensor Voltage Test
Connect an AC voltmeter between ECU connector terminals No. 6
and 24. See Fig. 2. Rotate left rear wheel at one revolution per
second. Measure voltage with wheel rotating. If voltage is 0.075 volt
or more, go to next test. If voltage is less than 0.075 volt, check
wheel speed sensor and/or toothed ring for damage, wear and proper
installation. If damage or wear is found, replace faulty component and
retest. If components are not properly installed, reposition and
retest. If components are okay, replace wheel speed sensor and retest.
Right Front Wheel Speed Sensor Voltage Test
Connect an AC voltmeter between ECU connector terminals No. 7
and 25. See Fig. 2. Rotate right front wheel at one revolution per
second. Measure voltage with wheel rotating. If voltage is 0.075 volt
or more, go to next test. If voltage is less than 0.075 volt, check
wheel speed sensor and/or toothed ring for damage, wear and improper
installation. If damage or wear is found, replace faulty component,
and retest. If components are improperly installed, reposition
component, and retest. If components are okay, replace wheel speed

ANTI-LOCK BRAKE SYSTEM
Article Text (p. 6)
1993 Volkswagen Corrado
For Volkswagen Technical Site: http://vw.belcom.ru
Copyright © 1998 Mitchell Repair Information Company, LLC
Wednesday, March 22, 2000 08:57PM
sensor, and retest.
Left Front Wheel Speed Sensor Voltage Test
Connect an AC voltmeter between ECU connector terminals No. 5
and 23. See Fig. 2. Rotate left front wheel at one revolution per
second. Measure voltage with wheel rotating. If voltage is 0.075 volt
or more, go to next test. If voltage is less than 0.075 volt, check
wheel speed sensor and/or toothed ring for damage, wear and proper
installation. If damage or wear is found, replace faulty component and
retest. If components are not properly installed, reposition and
retest. If components are okay, replace wheel speed sensor and retest.
ECU Relay Continuity Test
Turn ignition off. Using an ohmmeter, check for continuity
between ECU connector terminals No. 1 and 3, and between terminals No.
1 and 20. See Fig. 2. If there is continuity at both test points, go
to next test. If there is no continuity at either or both test points,
check wiring. If wiring is faulty, repair and retest. If wiring is
okay, replace relay and retest.
Solenoid Valves Ground Circuit Continuity Test
1) Turn ignition off. Remove jumper wire from previous test.
Using an ohmmeter, check for continuity between ECU connector
terminals No. 1 and 11. See Fig. 2. If there is continuity, go to step
3).
2) If continuity does not exist, check for continuity between
ECU connector terminal No. 1 and valve block housing and between
hydraulic modulator and valve block housing. If continuity does not
exist between ECU connector terminal No. 1 and valve block housing,
repair wiring, and retest. If continuity does not exist between
housings, repair as necessary.
3) Reconnect jumper wire between ECU connector terminals No.
1 and 11. Check for continuity between ECU connector terminal No. 11
and valve block connector terminal No. 1 (Brown wire). See Figs. 2 and
4. If there is no continuity, repair wiring and retest.
Hydraulic Modulator/Pump Relay Ground Circuit Test
Turn ignition off. Reconnect pressure switch connector.
Depress brake pedal 20 times. Using an ohmmeter, check for continuity
between ECU connector terminals No. 1 and 14. If continuity exists, go
to next test. If continuity does not exist, check for continuity
between pressure switch terminals No. 1 (Brown wire) and No. 4
(Red/Yellow or White wire). See Figs. 1 and 4. If continuity does not
exist, replace pressure switch, and retest. If continuity exists,
check wiring between ECU terminal No. 14 and pressure switch terminal
No. 4. Repair wiring, and retest.
Low Pressure Warning Switch Test
Turn ignition off. Ensure brake fluid level is okay and fluid
level sensor switch float is in correct position (switch is in closed
position). Ensure accumulator is fully charged and pump is not
operating. Using an ohmmeter, check for continuity between ECU