Antilock Braking System (ABS)

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CIRCUIT DESCRIPTION
The toothed wheel generates a voltage pulse as it moves past the sensor. Each tooth-gap-tooth series on the wheel generates a pulse. The frequency of these pulses is used by the EBTCM to determine wheel speed. The amplitude of the voltage generated in each pulse depends on the air gap between the sensor and the toothed wheel and depends on the wheel speed.

CONDITIONS FOR SETTING THE DTC
- Within 20 milliseconds, no speed is detected at the affected wheel at a speed above 40 km/h (25 mph).
- The vehicle reference speed is higher than 12 km/h (7.5 mph) when the vehicle first drives off while the speed of one affected front wheel remains at approximately 2 km/h (1.2 mph).
- An open in the circuit is present.
- A short to voltage in the circuit is present.
- A short to ground in the circuit is present
- There is a malfunctioning speed sensor.
- The test for this malfunction occurs when the vehicle is in motion. It will not set with the ignition switch in the RUN position and with the vehicle at rest.

ACTION TAKEN WHEN THE DTC SETS
- A malfunction DTC is stored.
- The ABS and the TC indicator lamps are turned on.
- The ABS and the TCS are disabled.

CONDITIONS FOR CLEARING THE DTC
- The condition for the DTC is no longer present.
- The scan tool Clear DTCs function is used.
- 100 drive cycles have passed with no DTCs detected.

DIAGNOSTIC AIDS
- Be sure the speed sensor wiring is properly routed and properly retained. This will help prevent false signals due to electrical noise being picked up by the wiring.
- Perform a thorough inspection of the wiring. Perform a thorough inspection of the connectors.
- Failure to carefully and fully inspect the wiring and the connectors may result in misdiagnosis. Misdiagnosis causes part replacement with reappearance of the malfunction.
- The scan tool can also be used to monitor the wheel speeds during a road test. Watch the wheel speeds being displayed on the scan tool to see if any of the readings are unusual. For example, one sensor varying in speed from the other three or a signal going intermittently high or low, etc.
- If the customer's comments reflect that the ABS indicator is on only during moist environmental changes (rain, snow, vehicle wash), inspect all the wheel speed sensor circuitry for signs of water intrusion. If the DTC is not current, clear all DTCs and simulate the effects of water intrusion by using the following procedure:

1. Spray the suspected area with a 5% saltwater solution.
Add two teaspoons of salt to twelve ounces of water to make a 5% saltwater solution.
2. Test drive the vehicle over various road surfaces (bumps, turns, etc.) above 24 km/h (15 mph) for at least 30 seconds.
3. If the DTC returns, replace the suspected harness.

TEST DESCRIPTION
The number(s) below refer to the step number(s) on the diagnostic table.
3. This step checks the integrity of the wheel speed sensor. If the ohms do not fall into the range of the specifications, there is a malfunctioning wheel speed sensor.
4. This step checks the output in volts of the of the wheel speed sensor.
15. This step checks if the wheel speed sensor harness is routed to close to a spark plug wire. The spark plug wires are a possible source of Electromagnetic Interference (EMI).