Brakes problem
2000 Ford Expedition V8 Four Wheel Drive Automatic 135000 miles

ABS LIGHT COMES ON WHEN I START THE CAR AS SOON AS I LET OFF THE BRAKE AND STAYS ON, ABS DOES NOT WORK, ANY IDEA ?

have the cars computer read for fault codes ? which ABS light is on red/yellow ??

DESCRIPTION
CAUTION:See ANTI-LOCK BRAKE SAFETY PRECAUTIONS article in GENERAL INFORMATION.

The 4-wheel Anti-Lock Brake System (ABS) is designed to allow vehicle to stop in the shortest possible distance while maintaining full steering control. ABS system consists of Electronic Hydraulic Control Unit (EHCU), master cylinder, power brake booster, front wheel speed sensors, rear wheel speed sensor (mounted on differential). ABS uses electronic and hydraulic components to prevent wheels from locking up during brake application. ABS does not function during normal (light) braking applications.
The EHCU consists of an Electronic Control Module (ECM) attached to a Hydraulic Control Unit (HCU). If service is required, ECM can be replaced if inoperative. If HCU is inoperative, entire EHCU must be replaced as an assembly.
NOTE:For more information on brake system, see appropriate DISC & DRUM article.
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OPERATION
ABS control module receives a signal from each speed sensor. This information is translated into calculated wheel speed. When ABS control module determines wheel lock-up is about to occur, the hydraulic control unit is activated and deactivated to vary hydraulic pressure to prevent wheel lock-up.
ABS does not operate during normal braking conditions. ABS is self-monitoring. ABS has a self-diagnostic system to obtain trouble codes for testing purposes. See DIAGNOSIS & TESTING .
The ABS and BRAKE warning lights alert vehicle operator of problems in braking system. Red BRAKE warning light monitors master cylinder fluid level and parking brake status. Yellow ABS warning light alerts vehicle operator to problems in ABS system.
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