Iowa CDL Combination Vehicles Test study plan

Recite the full pre-trip inspection sequence for a combination vehicle from memory, naming every item in the engine compartment, walk-around, and in-cab portions in the order you would actually perform them.

Perform a complete air brake system check sequence on paper: build pressure, run the static leak test, run the applied leak test, confirm the low-air warning device, and verify the spring brakes engage, stating the maximum allowable air-loss rate for each combination-vehicle test.

Draw a diagram of the tractor air brake system from memory, tracing air from the compressor through the governor, supply reservoirs, foot valve, relay valves, and brake chambers, and label the tractor protection valve's purpose.

Identify each item in the coupling area of a tractor (fifth wheel, jaws, safety latch, apron, mounting bolts, air and electrical lines) and state what a failure of each would look like during a walk-around.

Perform the full coupling procedure aloud in the correct order, from checking the fifth wheel to completing the pull test, without skipping the trailer-height check, the air line connection order, or the visual and physical tug checks.

Perform the full uncoupling procedure aloud in the correct order, including chocking the wheels, lowering the landing gear, disconnecting air and electrical lines, and pulling the tractor clear.

Explain why the pull test is done, what a failed pull test tells you, and what to correct before the vehicle moves.

Compare the three air brake tests (static leak, applied leak, low-air warning) and state the acceptable result for each on a combination vehicle, then describe exactly what you do if a test fails.

Explain how the tractor protection valve and the spring brakes behave as pressure drops, and why the trailer air supply valve must not be held open to nurse a leaky system.

Explain how the spring brake chambers work, why they apply when air pressure drops, and how the push-pull parking brake test confirms they are functioning.

Describe the correct braking technique for a long downgrade in a loaded combination vehicle, naming what brake fade is and why riding the brakes causes it.

Define a vehicle's rollover threshold and list at least six factors that lower it, including center of gravity height, load placement, track width, suspension, road surface, and speed through a curve.

Explain how speed through a curve combines with load height to produce a rollover, and state why a lightly loaded or empty trailer can be more dangerous in a curve than a fully loaded one.

Explain off-tracking: why the rear wheels of a trailer follow a path inside the front wheels, how the amount of off-tracking grows with wheelbase and with the sharpness of the turn, and how to compensate when making a right turn.

Define rearward amplification, rank single trailers, doubles, and triples by how much the last trailer swings, and state which maneuvers amplify the effect most.

Sketch the swept path of a 53-foot trailer through a 90-degree turn and mark how far the trailer's rear axle cuts the corner relative to the tractor's path.

Describe the correct driver response when the right-side wheels drop off the pavement edge, including what not to do with the steering wheel and brakes.

Distinguish a drive-wheel (tractor) jackknife from a trailer jackknife, listing the conditions that cause each and the specific driving inputs that prevent each.

Describe the recovery from a rear-wheel skid step by step, including releasing the brakes, holding the steering wheel steady toward the intended path, and straightening out as traction returns.

Explain controlled braking versus stab braking, when each is appropriate in a combination vehicle, and why locking the steer axle is the worst outcome.

Explain why a bobtail tractor needs more stopping distance and stops differently from a loaded combination, and describe how to adjust following distance and braking for it.

Describe the correct right-turn technique for a combination vehicle: setting up wide, watching the trailer's rear wheels in the mirrors, and keeping the trailer out of the adjacent lane without cutting the corner.

State the following-distance rule for combination vehicles and calculate the gap for a 70-foot rig at 55 mph, then convert it to a fixed reference point you can count on the road.

List the railroad crossing procedure for a combination vehicle: approaching at a speed that lets you cross without stopping, downshifting before the crossing and never on it, checking that the far side has room, and using flashers and horn as required.

Describe how to brake and downshift for a downgrade exit ramp and where the combination's weight shifts during braking and cornering.

Re-run a timed 100-question simulation under test conditions and categorize every miss by domain so you can see which domain is still leaking points.

Re-inspect the two procedural sequences you scored worst on in weeks 1 and 2, and recite them again without notes until they are clean.

Explain aloud, without notes, how a combination vehicle's brake system differs from a single-unit truck's and why that changes stopping distance and brake feel.

Convert every remaining error from weeks 1 through 6 into a question you can answer in one sentence.

Complete three timed mock exams of 50 questions each across all four domains and record the score and domain breakdown for each.

Drill only the two lowest-scoring domains from Week 7 until each practice subset clears 90 percent.

Re-recite the coupling and uncoupling procedures, the air brake test sequence, and the rollover and off-tracking rules one final time without notes.

Review the error log end to end and confirm you can state the correct answer and the reason for every entry.