Technical information

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Technician Guidelines for Antilock Braking Systems
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3. Error Detection Methods
One ABS benefit is the ability to electronically detect
component or system failures. This electronic detection occurs
either during self-test checks at start-up, or during continuous
passive monitoring.
At start-up, the ECU will activate the ABS malfunction
indicator lamp and briefly energize the ABS modulator valves
(ignition-on blowdown or “chuff test”). At the same time, the
ECU checks the wheel speed sensors and other essential
components for proper operation. If no problems are found,
and the ECU detects that wheel speed sensors were functioning
properly just prior to the last vehicle shutdown, the ABS
malfunction indicator lamp will go out. On earlier systems, the
lamp would not go out until the vehicle reached about 5 mph.
During vehicle operation, the various ABS components also
continually monitor each other for failures and “out-of-range”
operating parameters. Through this process, the ECU detects
abnormalities during operation and activates the ABS
malfunction indicator lamp as appropriate.
The ECU will generally detect two types of faults: active and
stored. An active fault is a current and continuous failure in
need of repair (such as a broken connector). A stored fault is a
failure that affects ABS operation intermittently (such as a loose
connector).Technicians typically can retrieve failure information
either through blink codes or an electronic diagnostic tool. For
explanations of manufacturer-specific diagnostic and
troubleshooting tools and procedures, consult the appropriate
manufacturer’s service information.
Top 10 Most Commonly Encountered Problems
That Trigger ABS Malfunction Indicator Lamps
1. Abraded or cut wires in convuluted tubing near frame clamps.
2. Cut or corroded wires near sharp frame members and frame-mounted
modulators.
3. Wire jacket worn through from overlapping sensor and modulator wires near
frame members and frame-mounted modulators
4. Corroded connectors and connections not properly sealed or damaged seals.
5. Damaged connector latches or connectors not completely sealed to mating
assemblies.
6. Terminals not completely latched or seated into connectors
7. Excessive sensor air gap, sensor clip tension or excessive wheel bearing endplay.
8. Damage to exposed wires exiting or entering wire tubing.
9. Worn, chipped or damaged sensor or modulator.
10. Non-functioning controller (ECU).