What should I check if the yellow RABS bulb does not light during the 2-second bulb test?

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 does it mean if the REAR ANTILOCK light is flashing on and off?

Go to Test E to check for intermittent power to the module, a grounded diagnostic lead, or a faulty module ground.

What do I check if both the REAR ANTILOCK light and the BRAKE light are on?

Go to Test C to check low brake fluid, the master cylinder float, the diode/resistor element, the antilock valve switch, the master cylinder switch, and brake light wiring.

What if no flashout code is present when performing Test D?

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

What should I do if the rear wheels lock up during the 10 mph road test?

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

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Ford RABS Rear Antilock Brake System Troubleshooting Flowchart (Tests A–G)

Rear Antilock Brake System (RABS) troubleshooting flow chart with flashout code tests A-F

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Ford RABS rear antilock brake system troubleshooting flowchart; routes from yellow RABS / red brake warning bulb behavior to Tests A through F using the flashout diagnostic code.

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This document is a scanned flowchart titled "Rear Antilock Brake System Troubleshooting Chart" for diagnosing Ford RABS (Rear Antilock Brake System) warning-light problems. Starting from ignition key cycling, it walks the technician through observing the 2-second yellow "REAR ANTILOCK" bulb test and the red "BRAKE" bulb test, then branches based on whether each light is on, off, flashing, or fails to illuminate. Each outcome directs the reader to a lettered diagnostic test: Test A (module harness connector, module ground, antilock light power, 15 amp warning fuse, bulb and wiring), Test B (parking brake, parking brake switch, diesel low vacuum switch), Test C (low brake fluid, master cylinder float, diode/resistor element, antilock valve switch), Test D/D2 (obtaining the flashout code; RABS 20 amp fuse, shorts, power to module), Test E (intermittent power, grounded diagnostic lead), Test F/F3 (stop light circuit, excitor ring, sensor output and gap, computer module), and Test G (master cylinder connector, fluid level sensor). It concludes with a 10 mph road test to check rear wheel lock-up, noting that intermittent problems relate to Flashout Code 6. Footnotes reference the "Warning Lights" and "Obtaining the Flashout Code" sections. A red arrow highlights the Test C box (brake light ON path).

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Frequently asked questions

What should I check if the yellow RABS bulb does not light during the 2-second bulb test?: 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 does it mean if the REAR ANTILOCK light is flashing on and off?: Go to Test E to check for intermittent power to the module, a grounded diagnostic lead, or a faulty module ground.
What do I check if both the REAR ANTILOCK light and the BRAKE light are on?: Go to Test C to check low brake fluid, the master cylinder float, the diode/resistor element, the antilock valve switch, the master cylinder switch, and brake light wiring.
What if no flashout code is present when performing Test D?: Go to Test D2 to check the master cylinder harness connector, the RABS 20 amp fuse, shorts in the module harness connector wiring, power to the module, voltage at the fluid level sensor, and a grounded diagnostic lead.
What should I do if the rear wheels lock up during the 10 mph road test?: Continue with Test F3 to check wiring from the module to the brake switch, the excitor ring, sensor output, sensor gap, mechanical problems in the rear brakes, and the computer module.