What should I do first if the RABS light is on while the vehicle is running?

Obtain the flashout code before shutting the engine off, then turn the ignition switch from OFF to RUN and observe the 2-second "REAR ANTILOCK" bulb test.

What does the chart say to check if the yellow RABS bulb does not light?

Go to Test A to check the module harness connector, module ground, antilock light power, the 15 amp warning fuse, power to the 15 amp warning fuse, and the antilock bulb and wiring.

What is checked if there is no flashout code?

Test D2: master cylinder harness connector, RABS 20 amp fuse, shorts in module harness connector wiring, power to module, voltage at fluid level sensor, and grounded diagnostic lead.

What happens if the rear wheels lock during the road test?

Continue with Test F3 to check wiring from module to brake switch, excitor ring, sensor output, sensor gap, mechanical problems in rear brakes, and the computer module.

What if the rear wheels don't lock during the road test?

The system is functioning OK; consider a possible intermittent wiring problem or a problem that only shows up during driving, and refer to flashout code 6 for possible areas of concern.

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Ford RABS Rear Antilock Brake System Troubleshooting Chart (1992 Bronco)

Rear Antilock Brake System (RABS) troubleshooting flowchart with bulb-test branches A through G

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Ford RABS rear antilock brake troubleshooting flowchart. Branches by yellow/red bulb behavior to Tests A-G checking module harness, 15A/20A warning fuses, fluid level sensor, and wheel lock-up.

AI caption October 2005 · Photo 144 of 277

This document is a Rear Antilock Brake System (RABS) troubleshooting flowchart, drawing number CH6257-D. It guides a technician through diagnosing RABS warning light behavior, starting with obtaining a flashout code if the RABS light is on while the vehicle is running, then cycling the ignition from OFF to RUN and observing the 2-second "REAR ANTILOCK" bulb test. Depending on whether the yellow RABS bulb and red BRAKE bulb light, the chart directs the user to specific diagnostic tests: Test A (module harness connector, module ground, antilock light power, 15 amp warning fuse, bulb and wiring), Test G (master cylinder connector, red brake warning light, fluid level sensor/wiring), Test E (intermittent module power, grounded diagnostic lead, module ground), Test C (low brake fluid, master cylinder float, diode/resistor element, antilock valve switch), Test B (parking brake and switch, diesel low vacuum switch), Test F (vehicle stop light circuit), Test D/D2 (flashout code retrieval, RABS 20 amp fuse, wiring shorts), and Test F3 (excitor ring, sensor output/gap, rear brake mechanical problems, computer module). It concludes with a road test at 10 mph to check for rear wheel lock-up; if rear wheels don't lock, the system is functioning and intermittent problems should be checked via flashout code 6.

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Frequently asked questions

What should I do first if the RABS light is on while the vehicle is running?: Obtain the flashout code before shutting the engine off, then turn the ignition switch from OFF to RUN and observe the 2-second "REAR ANTILOCK" bulb test.
What does the chart say to check if the yellow RABS bulb does not light?: Go to Test A to check the module harness connector, module ground, antilock light power, the 15 amp warning fuse, power to the 15 amp warning fuse, and the antilock bulb and wiring.
What is checked if there is no flashout code?: Test D2: master cylinder harness connector, RABS 20 amp fuse, shorts in module harness connector wiring, power to module, voltage at fluid level sensor, and grounded diagnostic lead.
What happens if the rear wheels lock during the road test?: Continue with Test F3 to check wiring from module to brake switch, excitor ring, sensor output, sensor gap, mechanical problems in rear brakes, and the computer module.
What if the rear wheels don't lock during the road test?: The system is functioning OK; consider a possible intermittent wiring problem or a problem that only shows up during driving, and refer to flashout code 6 for possible areas of concern.