Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSFORD2021EXPEDITION PLATINUM, RWDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 138 (AUXILIARY BRAKE SYSTEM)
2021 Ford Expedition Platinum, RWD
Section 138 (Auxiliary Brake System)
2021 Ford Expedition Platinum, RWDSECTION Section 138 (Auxiliary Brake System)
WARNING: This page is about a different car, the 2018 Ford F-550 Super Duty, 2018 Ford F-450 Super Duty, 2018 Ford F-350 Super Duty, and 2018 Ford F-250 Super Duty. However, it is still accessible from the selected car via links, so may be relevant.
- Description And Operation
- Diagnosis And Testing
- Auxiliary Brake System - Vehicles With: Trailer Brake Control
- DTC Chart: Trailer Brake Control Module (TBM)
- Symptom Chart: Trailer Brake System
- Pinpoint Tests
- Pinpoint Test A : The Trailer Brakes Are Inoperative
- Pinpoint Test B : The Trailer Brakes Are Always Engaged
- Pinpoint Test C : The Message Center Displays Wiring Fault On Trailer
- Pinpoint Test D : The Message Center Does Not Agree With Actual Trailer Connection
- Pinpoint Test E : U3003:17
- Pinpoint Test F : U3003:16
- Pinpoint Test G : U3008:13
- Pinpoint Test H : U0100:00
- Pinpoint Test I : U0121:00
- Pinpoint Test J : U0140:00
- Pinpoint Test K : U0155:00
- Auxiliary Brake System - Vehicles With: Trailer Brake Control
- Removal And Installation
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.