Automobile & Light Truck Certification Test A5 BrakesHydraulic System Diagnosis and RepairMedium
A technician is diagnosing a vehicle with a brake fluid leak. They trace the leak to a steel brake line that has a small, pinhole-sized perforation in a section that runs along the frame. The vehicle owner states the leak developed suddenly after driving on a heavily salted road. Which type of brake line damage is MOST likely occurring?
- AImpact damage from road debris.
- BFatigue fracture due to vibration.
- CExternal corrosion from road salt.
- DInternal erosion from contaminated fluid.
Show answer & explanationAnswer & explanation
Correct answer: C. External corrosion from road salt.
Pinhole leaks in steel brake lines, especially in areas exposed to road elements and reported after driving on salted roads, are highly indicative of external corrosion. Road salt (calcium chloride, magnesium chloride) is highly corrosive to steel.
Why the other options are wrong
- A. Impact damage usually results in a dent or a larger, more irregular tear, not a pinhole.
- B. Fatigue fractures typically occur at stress points or bends and might appear as a crack, not necessarily a pinhole in a straight section.
- D. Internal erosion from contaminated fluid is rare and would typically manifest as master cylinder or caliper seal failure, not a pinhole in the steel line itself.
Brake Line Corrosion
Degradation of steel brake lines due to exposure to moisture, road salt, and other environmental factors, leading to rust and potential leaks.
- Common in areas using road salt.
- Causes pitting and pinhole leaks.
- Requires replacement of damaged sections.
Memory trick: Salt on the road, rust in the code, leak will show.