310T Preventive Maintenance and Inspection 5 — Questions and Answers
Question 1: A technician is inspecting flexible air lines on a truck's brake system and finds a line with a small crack in the outer jacket but no visible damage to the inner tube. What is the correct action?
- Mark the location and replace the line at the next scheduled PM
- Wrap the crack with electrical tape and re-inspect in 1,000 miles
- Replace the hose immediately regardless of inner tube condition (Correct answer)
- Apply rubber sealant and pressure test to confirm integrity
Correct answer: Replace the hose immediately regardless of inner tube condition
Any cracked or damaged brake air hose must be replaced immediately because the outer jacket protects the inner tube from abrasion and further deterioration.
Question 2: During a PM inspection, the engine air filter restriction gauge shows a reading in the red zone. What is the correct procedure?
- Reset the indicator and continue operation for 5,000 more miles
- Remove, inspect, and clean the filter with compressed air before reinstalling
- Replace the air filter element and reset the restriction indicator (Correct answer)
- Check the indicator calibration before replacing any components
Correct answer: Replace the air filter element and reset the restriction indicator
A restriction indicator in the red zone confirms the filter element is plugged beyond serviceable limits and must be replaced, not cleaned.
Question 3: When checking the fifth wheel on a semi-truck during a PM inspection, what is being verified when the technician pulls on the kingpin release handle with the trailer coupled?
- That the jaws will open freely in an emergency
- That the locking mechanism is fully engaged and cannot be accidentally released (Correct answer)
- That the release cable has adequate slack
- That the fifth wheel slide mechanism is functional
Correct answer: That the locking mechanism is fully engaged and cannot be accidentally released
Pulling the kingpin release handle while coupled confirms the locking jaws are fully engaged and will not inadvertently release under load.
Question 4: A coach technician notices the DEF (Diesel Exhaust Fluid) level sensor reads correctly but the DEF appears amber in color instead of clear. What should the technician do?
- The amber color is normal — proceed with the PM
- Drain and replace the DEF, as contaminated fluid can damage the SCR catalyst (Correct answer)
- Add distilled water to dilute the DEF back to spec
- Test the DEF concentration with a refractometer before deciding
Correct answer: Drain and replace the DEF, as contaminated fluid can damage the SCR catalyst
DEF should be clear; amber discoloration indicates contamination that can crystallize in and damage the expensive SCR injector and catalyst.
Question 5: During a PM inspection of a heavy truck, a technician finds the front axle U-bolt nuts have been improperly torqued — one nut is 40 ft-lb below specification. What is the risk of operating with this condition?
- Premature spring wear only, with no immediate safety risk
- Axle shift, wheel misalignment, and potential loss of vehicle control (Correct answer)
- Reduced fuel economy due to increased rolling resistance
- Accelerated tire wear on the affected corner only
Correct answer: Axle shift, wheel misalignment, and potential loss of vehicle control
Improperly torqued U-bolt nuts allow the axle to shift position, causing sudden severe misalignment and potential loss of steering control.
Question 6: A technician is performing a PM on a bus and checks the wheelchair lift. The platform descends correctly but will not rise with a 200 lb test load. What is the FIRST system to inspect?
- Electric motor brushes and commutator condition
- Hydraulic fluid level and pump pressure output (Correct answer)
- Limit switch adjustment on the lift platform
- Control module for stored fault codes
Correct answer: Hydraulic fluid level and pump pressure output
Inability to lift a rated load under hydraulic pressure most directly points to low fluid level or insufficient pump pressure as the first diagnostic step.
Question 7: When inspecting tire tread depth on a steer axle during a PM inspection, what is the minimum tread depth allowed before the tire must be replaced per FMCSA regulations?
- 2/32 inch
- 4/32 inch (Correct answer)
- 6/32 inch
- 8/32 inch
Correct answer: 4/32 inch
FMCSA requires a minimum of 4/32 inch tread depth on steer axle tires, which is more stringent than the 2/32 inch requirement for other axle positions.
310T Preventive Maintenance and Inspection 5
A technician is inspecting flexible air lines on a truck's brake system and finds a line with a small crack in the outer jacket but no visible damage to the inner tube.
What is the correct action?