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.
Circuit/System Description
The manual apply switch rationality diagnostic monitors for circuit rationality faults on the manual apply switch input. The manual apply switch consists of a primary circuit, which is used as the basis for determining the trailer brake manual apply gain, and a redundant circuit that is used to rationalize performance of the primary circuit.
Manual Trailer Brake Apply Request Switch Signal Invalid" diagnostic monitors for a manual apply switch that is stuck in an applied position.
Manual Trailer Brake Apply Request Switch Signal -plausibility failure diagnostic monitors for circuit rationality faults on the manual apply switch input. The manual apply switch consists of a primary circuit, which is used as the basis for determining the trailer brake manual apply gain, and a redundant circuit that is used to rationalize performance of the primary circuit. The manual apply switch position fault is detected when the absolute value of the difference between the primary manual apply switch input and redundant inputs exceeds a threshold for a certain amount of time.
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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.