GM has announced that it will recall approximately 800,000 full-size trucks and SUVs from the 1999-2002 model years, due to a problem with the antilock braking system. As I understand the problem, it's caused by contamination of the wheel speed sensor, where ferrous debris (most of it likely from the rotors and semi-metallic pads) sticks to the sensor and either causes a mechanical misalignment of the sensor or a magnetic short circuit. In either case, the sensor's ability to determine the wheel speed is impaired. When this happens, it's likely that the ABS system interprets the lost signal as a locked wheel, and begins to decrease brake pressure. This obviously has the effect of increasing stopping distances. Because the problem is corrosion-related, the recall is only being performed in 14 northern states. This is the same problem that caused GM to recall 150,000 Canadian trucks earlier in the year, when perhaps it was thought that salt corrosion could be stopped at border checkpoints.

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