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Home >> Daewoo >> 1999 >> Lanos S Hatchback L4-1.6L DOHC D-TEC MFI >> Repair and Diagnosis >> A L L Diagnostic Trouble Codes ( DTC ) >> Testing and Inspection >> Manufacturer Code Charts >> Antilock Brakes and Traction Control >> DTC A028: Right Rear Excessive Wheel Speed Variation

DTC A028: Right Rear Excessive Wheel Speed Variation

DIAGNOSTIC TROUBLE CODE (DTC) A028 RIGHT REAR EXCESSIVE WHEEL SPEED VARIATION





Circuit Description
As a toothed ring passes by the wheel speed sensor, changes in the electromagnetic field cause the wheel speed sensor to produce a sinusoidal (AC) voltage whose frequency is proportional to the wheel speed. The magnitude of this signal is directly related to wheel speed and the proximity of the wheel speed sensor to the toothed ring (often referred to as the air gap).

Diagnosis
This test detects a situation in which the right rear wheel speed changes more than 19 km/h (12 mph) in 8 milliseconds. This change must occur five times with less than 0.2 second between occurrences. This test will not fail if any wheel speed hardware faults (codes A032 - A035) have already failed.

Cause(s)
- A sensor is loose.
- There are worn suspension/drivetrain components.
- There is an intermittent short in the wheel speed input wires.
- The sensor is physically damaged.
- The wheel speed ring is damaged.
- A connector is damaged.
- The Electronic Brake Control Module (EBCM) is malfunctioning.

Fail Action
This is a critical operational fault. The Antilock Brake System (ABS) is disabled and the ABS warning lamp is turned on. A rehome is commanded to ensure that the motors are in the home position.

Test Description
The number(s) below refer to step(s) on the diagnostic table.
1. This test verifies whether the malfunction is currently present.
2. This test checks to see if excessive wheel bearing end play caused the Diagnostic Trouble Code (DTC).
4. This step will identify a wheel speed sensor or circuitry that is damaged and visibly apparent.
5. This test checks the wheel speed sensor for the proper resistance values.
7. This test ensures the wheel speed sensor and the sensor ring generate the proper voltage.
8. This step ensures the wheel speed sensor is not shorted to ground.
9. This step checks for proper voltages at the speed sensor harness connector.
10. This test ensures that the wheel speed sensor circuitry is not internally shorted.
22. This checks for an open in circuit BRN.
24. This checks for a short to ground in both wheel speed signal circuits.
26. This step ensures that DTC A028 was not set due to a poor connection between the EBCM and the EBCM harness connector J1.
32. This checks for an open in circuit WHT.

Diagnostic Aids
An "intermittent" malfunction may be caused by a poor connection, wire insulation that has been rubbed through, or a wire that is broken inside the insulation.
The frequency of the malfunction can be checked by using the enhanced diagnostic function of the scan tool as described in "Scan Tool Diagnostics." Scan Tool Diagnostics
If the customer's comments reflect that the ABS indicator is on only during moist environmental changes (rain, snow, vehicle wash, etc.), all wheel speed sensor circuitry should be thoroughly inspected for signs of water intrusion. Use the following procedure:
1. Spray down the suspected area with a 5 percent salt water solution (10 ml [2 teaspoons] of salt to 355 ml [12 fluid ounces] of water).
2. Start the vehicle and allow it to run for 10 seconds.
3. If the DTC returns immediately, replace the suspected harness.
Any circuitry that is suspected of causing the intermittent complaint should be thoroughly checked for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wiring connections, or physical damage to the wiring harness.
When measuring wheel speed sensor resistance, ensure that the vehicle is at room temperature (approximately 20°C [68°F]). Wheel speed sensor resistance will vary with temperature.
When replacing a wheel speed sensor, inspect the sensor terminals and harness connector for corrosion and/or water intrusion. If evidence of corrosion or water intrusion exists, replace the wheel speed sensor and the jumper harness as necessary.
It is difficult to measure the resistance and the voltage at the terminals of the wheel speed sensor due to sensor mounting location and position. Terminals at the other end of the jumper harness are much more accessible. The rear wheel speed sensor jumper harnesses are connected to the system through connector C902, which is clipped to the vehicle near the right rear wheel. It connects to the floor harness, which passes through a grommet near that point. The clamp securing it to the vehicle is removed easily by pinching the tabs together and pushing up on the clamp. It is easier to handle the connector and take measurements if you free the connector from the axle first. Refer to "Rear Wheel Speed Sensor Jumper Harness" for illustrations. Wheel Speed Sensor
After you unplug the jumper harness from the floor harness at C902, stand toward the rear of the car. Rotate the connector so you are looking at the open end, and you will see it as it appears in the sketch at the top of this procedure. It will then be easy to make the necessary measurements.
The jumper harnesses for both rear wheels are bound together at this connector and are replaced as a single assembly, not as separate right or left jumper harnesses.

IMPORTANT: Wheel speed sensor intermittent malfunctions may be difficult to locate. Take care not to disturb any electrical connections prior to an indicated step of this chart. This will insure that an intermittent connection will not be corrected before the source of the malfunction is found.














DTC A028 - Right Rear Excessive Wheel Speed Variation
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