chap82 pps Automotive technology at University of Cambridge

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Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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OBJECTIVES:
After studying Chapter 82, the reader should
be able to:

•
•
•
•

Prepare for ASE Brakes (A5) certification test content area
“F” (Antilock Brake System Diagnosis and Repair).

Describe normal ABS dash lamp operation.
Discuss visual inspection of the various types and brands of
ABS.
Explain how to retrieve trouble codes.

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OBJECTIVES:
After studying Chapter 82, the reader should
be able to:

•

•
•

List the methods used to clear trouble codes.
Explain the various methods for bleeding ABS.
Discuss methods and tools needed to diagnose an ABSequipped vehicle.

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
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KEY TERMS:
amber ABS warning lamp
breakout box (BOB)
red brake warning lamp (RBWL)

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
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ABS DIAGNOSTIC PROCEDURE
Customer concerns about a fault with the antilock braking system
can be best handled by performing the following:
Step #1 Verify the customer concern This is very important
because often a problem with the base brakes is thought by the
customer to be a fault with the antilock braking system. It is
helpful for the owner to drive the vehicle with a service tech
if the problem is not readily apparent.

Continued

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Step #2 Perform a visual inspection If both the red and the
amber brake warning lights are on, look for a fault in the
hydraulic system, including leaks at the following locations:
•
•
•
•
•

Master cylinder
Electrohydraulic control unit

Flexible brake hoses
Brake lines and fittings
Calipers and/or wheel cylinders

Step #3 Check for stored diagnostic trouble codes (DTCs) Use
a scan tool or other necessary methods to retrieve diagnostic
trouble codes. If found, follow the specified factory procedures to
isolate and determine the cause.
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Step #4 Complete the repair This step may involve replacing a
hydraulic component. If so, then the hydraulic system should be

bled using the factory specified procedure. Clear all diagnostic
trouble codes.
Step #5 Verify the repair Always test-drive the vehicle under
the same conditions that were needed to verify the problem to be
sure that the cause has been corrected.

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BRAKE WARNING LAMP OPERATION
The first step in the visual diagnosis of an antilock braking
system problem is to check the status of the brake warnin
lamps.

Red Brake Warning Lamp A red brake warning lamp
(RBWL) warns of a possible dangerous failure in the base
brakes, such as low brake fluid level or low pressure in half of the
hydraulic system.
The red brake warning lamp will also light if the parking brake is
applied and may light due to an ABS failure, such as low brake
pressure on an integral system.
See Figure 82–1.
Continued
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Figure 82–1 Typical brake warning lamp operation chart. Not all vehicles use the same light
sequence. The top of the chart indicates normal warning lamp operation if the system is okay.

See the chart on
Page 1004 of
your textbook.

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Amber ABS Warning Lamp The amber ABS warning lamp
usually comes on after a start during the initialization or startup
self-test sequence. The exact time the lamp remains on after the
ignition is turned on varies with the vehicle and the ABS design.
Figure 82–2 On most vehicles equipped with ABS, the ABS and the BRAKE warning lamp

should come on as a bulb check when the ignition in first switched on.

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THOROUGH VISUAL INSPECTION
A thorough visual inspection should include the following items:

See the list on Page 1005 of your textbook.
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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Figure 82–3 A thorough visual inspection should include carefully inspecting around the
electrohydraulic unit for signs of obvious problems or the installation of aftermarket devices
such as alarm systems.

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Quick and Easy Wheel Speed Sensor
Diagnosis
A fault in a wheel speed sensor (WSS) is a common ABS problem. A quick and
easy test that works on most Bosch ABS (and perhaps others) involves the
following steps:
Step #1 Hoist the vehicle safely.
Step #2 Turn the ignition on (engine off).
Step #3 Spin a tire by hand as fast as possible.
Step #4 The ABS amber warning light should come on, indicating
a speed was detected but not by all the wheel speed sensors.
Step #5 Turn the ignition off to reset the ABS warning light.
Step #6 Repeat the test on each of the remaining wheels.
If any wheel fails to turn on the ABS light, carefully inspect the wheel speed
sensor for proper resistance and the tone ring and wiring. If the ABS light is
on all the time and does not reset when the ignition is turned off, the
problem is not caused by a wheel speed sensor.
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
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NOTE: Most wheel speed sensors are magnetic and therefore can attract
and hold metallic particles. Be sure to remove any metallic debris from
around the magnetic wheel speed sensor.

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TEST DRIVE AND VERIFY THE FAULT
A test-drive is a very important diagnostic procedure. Many ABS
and diagnostic trouble codes (DTCs) will not set unless the vehicle
is moving. Often, the driver has noticed something like the self-test
while driving and believed it to be a fault in the system.

Before driving, start the engine and observe the red and amber
brake warning lamps. If the red brake warning lamp is on, the
base brakes may not be functioning correctly. Do not drive the
vehicle until the base brakes are restored to proper operation.
NOTE: Some ABS units, such as the Delphi VI, will cause the brake
pedal to move up and down slightly during cycling of the valves during the
self-test. Each system has unique features. The tech will have to learn to
avoid attempting to repair a problem that is not a fault of the system.
Continued
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What’s That Noise and Vibration?
Many vehicle owners and service techs have been disturbed to hear and feel an
occasional groaning noise. It is usually heard and felt through the vehicle after first
being started and driven. Because it occurs when first being driven in forward or
reverse, many techs have blamed the transmission or related drive line
components. This is commonly heard on many ABS vehicles as part of a system
check.

As soon as the ABS controller senses speed from the wheel speed
sensors after an ignition cycles on, the controller will run the pump either
every time or whenever the accumulator pressure is below a certain level.
This can occur while the vehicle is being backed out of a driveway or being
driven forward because wheel sensors can only detect speed—not
direction. Before serious and major repairs are attempted to “cure” a noise,
make sure it is not the normal ABS self-test activation sequence of events.

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
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NOTE: Some systems are diagnosed by “antilock” and “brake” warning
lamps, vehicle symptoms, and the use of a breakout box.

See the diagnostics charts on Page 1006 of your textbook.
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RETRIEVING DIAGNOSTIC TROUBLE CODES
After performing a visual inspection and verifying the customer’s
complaint, retrieve any stored ABS-related diagnostic trouble
codes (DTCs). The exact procedure varies with the type of ABS
and with the make, model, and year of the vehicle.
Always consult factory service information for the vehicle being
diagnosed. Some systems can only display flash codes (flashing
ABS or brake lamp in sequence), whereas other systems can
perform self-diagnosis and give all information to the technician
through a scan tool.
NOTE: With some ABS systems, the diagnostic trouble code is lost if the
ignition is turned “off” before grounding the diagnostic connector.
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KELSEY-HAYES ANTILOCK (NONINTEGRAL)
The Kelsey-Hayes rear-wheel antilock uses two solenoids and
valves to control the rear-wheel brakes. KH four-wheel antilock
uses the computer to pulse the valves. The pulsing is called pulsewidth modulated (PWM) and the valve is called a PWM valve.
Retrieving Diagnostic Trouble Codes
GM trucks’ (RWAL) DTCs are retrieved
by flash codes or scan data through the
use of a scan tool or connect H to A at
the data link connector (DLC).
Figure 82–4 General Motors diagnostic connector. Flash codes
are available by using a jumper wire to ground (terminal A) to
terminal H. This connector is located under the dash near the
steering column on most General Motors vehicles.

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NOTE: Be sure that the brake warning lamp is on before trying to
retrieve DTCs. If the lamp is not on, a false code 9 could be set.
Figure 82–5 Connecting a jumper wire from
the diagnostic connector to ground. The exact
location of this diagnostic connector varies
with the exact vehicle model and year.

Ford trucks’ (RABS) DTCs are
retrieved by jumper lead flash codes
only.
Chrysler light trucks’ DTCs are
retrieved by ground diagnostic
connections.

See Figure 82–6.
Continued
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NOTE: If the ignition is turned off, the failure code will be lost unless it
is a hard code that will be present when the ignition is turned back on.

Figure 82–6 Chrysler diagnostic connector
location varies with the model and year.

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Kelsey-Hayes Diagnostic
Trouble Codes

See these charts on Page 1007
of your textbook.

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RWAL Diagnostics
The owner of an S-10 pickup truck complained that the red brake warning lamp on
the dash remained on even when the parking brake was released. The problem could
be one of the following:

1. A serious hydraulic problem
2. Low brake fluid
3. A stuck or defective parking brake switch
4. If the brake lamp is dim, RWAL trouble is indicated.
The tech found that the brake lamp was on dimly, indicating that an
antilock braking problem was detected. The first step in diagnosing an
antilock braking problem with a dash lamp on is to check for stored trouble
codes. The tech used a jumper between terminals A and H on the DLC
(ALCL), and four flashes of the brake lamp indicated a code 4.
Checking a service manual, code 4 was found to be a grounded switch
inside the hydraulic control unit. The hardest part was getting access to,
and replacement of, the defective (switch. After bleeding the system and a

thorough test-drive, the lamp sequence and RWAL functioned correctly.
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BOSCH 2 ABS (NONINTEGRAL)
The Bosch 2U/2S ABS is used on many domestic and imported
brands of vehicles.

Retrieving Diagnostic Trouble Codes On GM vehicles, DTCs
can be retrieved by connecting A to H at the data link connector
(DLC).
On most Bosch 2 systems, a scan tool can and should be used if
available to retrieve DTC.

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TEVES MKIV
The Teves Mark IV is a nonintegral (remote) ABS.

Retrieving Diagnostic Trouble
Codes Trouble codes are
accessed only by a bidirectional
scan tool connected to the data
link connector (DLC).
Figure 82–7 A scan tool is the recommended
method to use to access General Motors
Teves Mark IV systems.

Continued
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