20/07/2026 9:44 am
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Automotive Q&A
Low-speed ABS activation with one wheel-speed trace dropping out
Review the evidence, add a focused answer, and distinguish confirmed measurements from assumptions.
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A 2011 Silverado 1500 has unwanted ABS activation during the final few feet of a gentle stop. There is no stored chassis DTC. On a slow graph, all four sensors agree until about 5 mph, then the left-front trace intermittently falls to zero while the others decline smoothly. Tire sizes and pressures match.
Before replacing the hub assembly, what is the best way to distinguish a sensor air-gap or mounting problem from a damaged encoder or wiring fault? The harness does not react to a stationary wiggle test.
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21/07/2026 7:57 am
The graph has already isolated the corner, but not the failed part. Inspect sensor seating and the mounting surface for rust that can increase the air gap. Compare the suspect signal with the right front at the same low wheel speed using the test method specified for that sensor type; signal amplitude or pulse quality often separates an air-gap problem from a clean electrical open.
Inspect the encoder through the sensor opening where possible and check bearing play. Test wiring dynamically while viewing the waveform, because a stationary continuity test may miss motion-related loss. Repair the evidence you find, then repeat the identical low-speed stop while graphing all four channels.
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23/07/2026 10:31 am
Rust under the left-front sensor flange had lifted it slightly. The encoder and bearing were clean and had no abnormal play. After cleaning the mounting pad and reinstalling the sensor to the specified gap, the two front traces matched down to zero and the false activation was gone.