Chap82

[object Object],[object Object],[object Object],[object Object],OBJECTIVES: After studying Chapter 82, the reader should be able to: Continued

[object Object],[object Object],[object Object],OBJECTIVES: After studying Chapter 82, the reader should be able to:

ABS DIAGNOSTIC PROCEDURE ,[object Object],Continued 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.

[object Object],Continued ,[object Object],[object Object],[object Object],[object Object],[object Object],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.

BRAKE WARNING LAMP OPERATION ,[object Object],Continued

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. Continued See the chart on Page 1004 of your textbook.

[object Object],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. Continued

THOROUGH VISUAL INSPECTION ,[object Object],Continued See the list on Page 1005 of your textbook.

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. Continued

[object Object],Quick and Easy Wheel Speed Sensor Diagnosis 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.

Continued 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.

TEST DRIVE AND VERIFY THE FAULT ,[object Object],Continued 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. 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.

[object Object],What’s That Noise and Vibration? 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.

See the diagnostics charts on Page 1006 of your textbook. NOTE: Some systems are diagnosed by “antilock” and “brake” warning lamps, vehicle symptoms, and the use of a breakout box.

RETRIEVING DIAGNOSTIC TROUBLE CODES ,[object Object],NOTE: With some ABS systems, the diagnostic trouble code is lost if the ignition is turned “off” before grounding the diagnostic connector. 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.

KELSEY-HAYES ANTILOCK (NONINTEGRAL) ,[object Object],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. Continued

[object Object],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. Continued

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

[object Object],See these charts on Page 1007 of your textbook. Continued

[object Object],RWAL Diagnostics 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.

BOSCH 2 ABS (NONINTEGRAL) ,[object Object],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.

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

See these charts on Page 1008 of your textbook. Continued

DELPHI (DELCO) ABS VI (NONINTEGRAL) ,[object Object],Continued Retrieving Diagnostic Codes The Delphi (Delco) VI antilock braking system has extensive self-diagnostic capability. Access to this vast amount of information requires the use of a scan tool designed to interface (work) with the Delphi VI system. See Figures 82–8 and 82–9 and DTC code chart.

Figure 82–8 Delphi (Delco) VI system components. Notice that each front brake is controlled by a separate piston, whereas the rear brakes are controlled by the same piston. Continued

Figure 82–9 The Delphi (Delco) VI attaches to the side of the master cylinder and connects hydraulically through transfer tube assemblies. Continued

See the chart on Page 1009 of your textbook.

[object Object],The Nervous Taurus A thorough visual inspection revealed that the tone wheel (sensor ring) was cracked. This crack created a different wheel speed signal to the ABS controller than the other wheels and the controller activated the ABS as it would normally—that was why there were no DTCs. Other things that could have caused this problem, which is often called “false modulation,” include a bent wheel, mismatched tire sizes, or metal debris around the sensor.

[object Object],Look for Flood Damage If Electrical Problems ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],The Mystery ABS Amber Warning Light - Part 1 Some ABS will not retain a DTC unless the problem is currently present and the ABS amber warning light is on. All the brakes were in excellent condition, but brake fluid level was down a little. After topping off the master cylinder with clean DOT 3 brake fluid, the vehicle was returned to the customer with the following information: ,[object Object]

The Mystery ABS Amber Warning Light - Part 2 While the brake fluid level sensor normally would turn on the red brake warning light, in some systems it turns on the amber ABS light if the brake fluid falls below a certain level in the ABS reservoir. ,[object Object]

WHEEL SPEED SENSOR DIAGNOSIS ,[object Object],[object Object],Continued

Figure 82–10 Typical wheel speed sensor. When a tooth on the sensor ring is close to the sensor, the strength of the magnetic field is stronger because the metal of the tooth conducts magnetic lines of force better than air. When the tooth moves away, the magnetic field strength is reduced. It is this changing magnetic field strength that produces the changing voltage. Frequency of the signal is determined by the speed of the rotating sensor. Continued

[object Object],Figure 82–11 (a) A breakout box is being used to diagnose an ABS problem. The controller (computer) is located in the trunk of this vehicle, and a digital multimeter is being used to measure resistance and voltage at various points in the system, following the service manual procedure. Continued Follow manufacturer’s instructions for connecting the breakout box and probing appropriate pins. See Figure 82-11b

Figure 82–11 (b) Another vehicle being tested for an ABS fault. In this vehicle, the computer is located under the passenger seat, which has been removed to gain better access to the wiring and terminals. Continued

Figure 82–12 Measuring the resistance of a wheel speed sensor. ,[object Object],Continued

[object Object],Continued ,[object Object],[object Object],[object Object]

[object Object],Figure 82–13 A scope can be used to check for proper operation of a wheel speed sensor. Continued

[object Object],Figure 82–14 A broken tooth on a wheel speed sensor tone ring shows on the scope trace as a missing wave. Continued

WHEEL SPEED SENSOR ADJUSTMENT ,[object Object],Continued Figure 82–15 Use a nonmagnetic brass or plastic feeler gauge to check wheel speed sensor gap. A steel gauge would be attracted by the magnet in the sensor and would produce a drag on the gauge as it is moved between the sensor and the tone ring. This drag could be interpreted as a correct clearance reading. Adjust the sensor position so there is slight drag on the feeler gauge, and tighten the setscrew to lock the sensor in place.

Figure 82–16 (a) Always use a nonferrous (brass or plastic) feeler (thickness) gauge when measuring the gap between the toothed ring and the wheel speed sensor. (b) Sometimes a sensor is equipped with a paper spacer that is the exact thickness of the spacing required between the toothed ring and the sensor. If equipped, the sensor is simply installed with the paper touching the toothed wheel. A typical gap ranges from 0.020 to 0.050 in. (0.5 to 1.3 mm). ,[object Object],(a) (b) Continued

HYDRAULIC ABS SERVICE ,[object Object],Continued

[object Object],Continued CAUTION: Some ABS units require that the brake pedal be depressed as many as 40 times to discharge brake fluid fully from the accumulator. Failure to discharge the accumulator fully can show that the brake fluid level is too low. If additional brake fluid is added, the fluid could overflow the reservoir during an ABS stop when the accumulator discharges brake fluid back into the reservoir.

[object Object],Continued ,[object Object],[object Object],[object Object],NOTE: To avoid bleeding the hydraulic unit, use a brake pedal depressor during service to avoid losing brake fluid. This precaution keeps air from getting into the hard-to-bleed passages of the hydraulic unit.

Figure 82–17 Special bleed valve tools are often required when bleeding some ABS units such as the Kelsey-Hayes 4WAL system. ,[object Object],Continued

Figure 82–18 Two bleed valve tools are needed to bleed the Kelsey-Hayes 4WAL system, which attaches to the bleed valves on the accumulator. ,[object Object],Consult service information for the specified bleeding procedure and sequence. Continued

ABS SAFETY PRECAUTIONS ,[object Object],[object Object],[object Object],[object Object],[object Object]

SUMMARY ,[object Object],[object Object],[object Object],[object Object],Continued

SUMMARY ,[object Object],[object Object],( cont. )

Chap82

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