Engine systems is 9 of the 55 scored G1 questions (16%). Its 22 tasks are the jobs of an engine service: oil and filter, cooling-system tests and parts, belts and hoses, intake and throttle body, PCV, exhaust leaks, spark plugs, EVAP and DEF.
9scored questions
16%of the scored test
14practice questions here
What the task list covers
The 22 tasks of area A in the 2026 G1 guide, grouped:
Oil service: change oil and filter, reset the oil-life monitor (A.5).
Cooling: radiator, heater core, cap and recovery tank; pressure and dye tests; coolant test, flush and bleed; thermostat and bypass; belt-driven water pump; fans, fan clutch, shroud and air dams (A.6, A.8–A.12).
Belts: drive belts, tensioners and pulleys (A.7).
Air and fuel: throttle body service, air filters and intake parts, fuel tank, filler neck, cap, lines and external fuel filter (A.14, A.15, A.20).
Emissions and exhaust: PCV parts, exhaust leaks, hangers and heat shields, EVAP canister and lines, diesel exhaust fluid (A.16, A.17, A.21, A.22).
Ignition and codes: replace spark plugs, inspect secondary ignition, retrieve and record DTCs (A.18, A.19).
Checks: verify the concern, leaks, abnormal noises, pans and covers, engine warning lights (A.1–A.4, A.13).
Engine systems questions
0 of 14 answered · 0 correct
Question 1 of 14 · Engine Systems · 16%Not answered
Technician A says that a 70% antifreeze concentration transfers heat more efficiently than a 50% concentration. Technician B says that exceeding 60% antifreeze concentration can reduce the coolant's ability to carry heat away from the engine. Who is correct?
Explanation
Incorrect: Technician A is wrong: a 70% mix carries heat less well than 50/50, because water transfers heat better than glycol.
Correct: Technician B is right: water carries heat better than glycol, so going above about 60% antifreeze reduces the coolant's ability to move heat.
Incorrect: Technician A's claim is backward, so both cannot be correct.
Incorrect: Technician B's statement is correct, so rejecting both is wrong.
Question 2 of 14 · Engine Systems · 16%Not answered
A technician is refilling and bleeding the cooling system on a vehicle equipped with a heater control valve. Which step must be performed to ensure trapped air is removed from the heater core circuit?
Explanation
Correct: Setting the heater to full hot opens the heater control valve so coolant, and the trapped air, can flow through the heater core and out at the bleed point.
Incorrect: The engine must run to circulate coolant; with the ignition in accessory the pump does not turn.
Incorrect: Recirculate mode moves an air door, not coolant; the heater control valve follows the temperature setting.
Incorrect: Blower speed changes airflow across the core; it does not open the heater control valve.
Incorrect: The A/C compressor has nothing to do with coolant flow through the heater core.
Question 3 of 14 · Engine Systems · 16%Not answered
During an inspection of the accessory drive belt system, the technician notices the automatic belt tensioner arm vibrating excessively while the engine is idling. A squeaking noise is also heard. What is the most likely cause?
Explanation
Incorrect: An overfilled power steering reservoir can foam or overflow; it has no effect on the belt tensioner.
Incorrect: A misaligned power steering pulley chirps and wears the belt edges, but it does not make the tensioner arm bounce.
Incorrect: A seized idler pulley bearing drags or squeals at that pulley; the belt scrubs over it rather than making the tensioner flutter.
Incorrect: Glazed belt ribs squeal as they slip, but they do not make a sound tensioner arm oscillate.
Correct: A weak tensioner spring (or worn damper) cannot hold steady belt tension, so the arm flutters at idle and the belt slips and squeaks.
Question 4 of 14 · Engine Systems · 16%Not answered
A customer is relocating to a high-altitude region and inquires about cooling system performance. Which statement correctly describes the function of the radiator pressure cap regarding coolant properties?
Explanation
Incorrect: The water pump sets coolant flow rate; the cap only holds pressure.
Correct: Raising system pressure raises the coolant's boiling point, about 3°F per psi, which matters more at high altitude where air pressure is lower.
Incorrect: Freeze protection comes from the antifreeze concentration, not from the cap.
Incorrect: Electrolysis is stray electrical current through the coolant; the cap does not stop it.
Incorrect: The cap raises and holds system pressure; it does not lower it.
Question 5 of 14 · Engine Systems · 16%Not answered
A vehicle's upper radiator hose is found collapsed flat after the engine has cooled down overnight. The overflow hose to the coolant recovery tank is clear and connected. Which cooling system component is the most likely cause of this vacuum condition?
Explanation
Incorrect: The thermostat bypass routes coolant during warm-up; it does not create vacuum when the engine is off.
Correct: As coolant cools and shrinks, the cap's vacuum relief valve should open to draw coolant back from the recovery tank; if it sticks shut, the vacuum collapses the upper hose.
Incorrect: A worn water pump shaft seal leaks coolant out; it does not pull a vacuum on the upper hose.
Incorrect: A blocked recovery tank hose would cause the same collapse, but it is clear and connected here.
Incorrect: An internal radiator restriction causes overheating under load, not a vacuum after the engine cools.
Question 6 of 14 · Engine Systems · 16%Not answered
A technician installs a replacement 22 psi radiator cap on a vehicle cooling system originally designed for a 13 psi cap. What is the most likely negative consequence resulting from this specific action?
Explanation
Incorrect: A fan clutch responds to the temperature of air off the radiator, not to the pressure cap rating.
Incorrect: The thermostat works on coolant temperature; extra system pressure does not wear out its spring.
Incorrect: Lower hose collapse comes from suction at the pump or a weak hose; higher pressure pushes hoses outward.
Correct: A 22 psi cap holds far more pressure than the 13 psi system was built for, and the heater core, often the weakest part, can swell and rupture.
Incorrect: Higher system pressure suppresses water pump cavitation; it does not cause it.
Question 7 of 14 · Engine Systems · 16%Not answered
Technician A says that 100% antifreeze will freeze at a warmer temperature than a 50/50 mix. Technician B says that using 100% antifreeze concentrate provides the best freeze protection for vehicles in arctic climates. Who is correct?
Explanation
Correct: Technician A is right: undiluted ethylene glycol antifreeze freezes at roughly 0°F or warmer, well above the −34°F of a 50/50 mix.
Incorrect: Technician B is wrong: pure antifreeze concentrate gives poorer freeze protection than a proper mix with water.
Incorrect: Technician B's claim contradicts Technician A's correct one, so both cannot be right.
Incorrect: Technician A states the fact correctly, so rejecting both is wrong.
Question 8 of 14 · Engine Systems · 16%Not answered
A technician diagnoses an engine overheating condition immediately following a serpentine belt replacement. On this engine the water pump pulley is smooth and is driven by the back side of the belt. Which of these conditions is the most likely cause?
Explanation
Incorrect: A slipping fan clutch causes overheating at idle, but nothing links it to the belt replacement just done.
Incorrect: An automatic tensioner sets belt tension; a tight belt wears bearings but still turns the pump the right way.
Incorrect: The coolant was not touched in a belt replacement, and the wrong coolant type would not cause sudden overheating.
Incorrect: The thermostat was not removed for a belt job, so it cannot have been installed backwards.
Correct: If the new belt is routed so the wrong side meets the smooth pulley, the water pump turns backward and moves little coolant, so the engine overheats right after the job.
Question 9 of 14 · Engine Systems · 16%Not answered
After repairing an emissions failure and clearing Diagnostic Trouble Codes (DTCs), a customer needs the vehicle inspected immediately. What must occur before the vehicle can pass an OBD-II state inspection?
Explanation
Incorrect: Disconnecting the battery clears memory and resets the monitors again, the opposite of what is needed.
Incorrect: A MIL that stays off is not enough; inspection stations also reject vehicles with incomplete monitors.
Correct: Clearing codes resets the readiness monitors; the vehicle must be driven through the conditions that let them run and complete before an OBD-II inspection.
Incorrect: No fixed mileage sets the monitors; the required drive cycle depends on the vehicle.
Incorrect: Letting the engine idle 15 minutes does not complete most monitors, which need specific drive conditions.
Question 10 of 14 · Engine Systems · 16%Not answered
A customer complains of a fuel smell near the rear of the vehicle. During inspection, no liquid fuel or wet spots are visible on the tank, lines, or ground. Technician A says this could be caused by a small crack in the EVAP canister. Technician B says a fuel smell is only a concern if liquid fuel is dripping. Who is correct?
Explanation
Correct: Technician A is right: a cracked EVAP canister or hose can release fuel vapor and cause a smell with no liquid leak.
Incorrect: Technician B is wrong: fuel vapor leaks are a fire and emissions concern even with nothing dripping.
Incorrect: Technician B dismisses a real hazard, so both cannot be right.
Incorrect: Technician A's explanation is valid, so rejecting both is wrong.
Question 11 of 14 · Engine Systems · 16%Not answered
While inspecting an engine air filter housing, a technician finds dust trails inside the clean side of the ducting, downstream of the filter. The filter element itself appears clean and new. Which condition is the most likely cause?
Explanation
Incorrect: Throttle body gap affects idle airflow downstream; it cannot pull dust around the filter.
Correct: Dust on the clean side with a clean filter means air is bypassing the element, most often at a filter seal that is not seated in the housing.
Incorrect: The PCV system carries crankcase vapor into the intake; it does not bring dust into the clean-side ducting.
Incorrect: A saturated filter element restricts airflow, but it still traps dirt and does not let dust past to the clean side.
Incorrect: An intake manifold gasket leak is past the throttle body and draws in air there, not dust into the filter ducting.
Question 12 of 14 · Engine Systems · 16%Not answered
Technician A says that Mass Air Flow (MAF) sensors should be replaced every 50,000 miles as preventative maintenance. Technician B says that MAF sensors should be replaced only when diagnostic testing confirms they have failed or are out of calibration. Who is correct?
Explanation
Incorrect: Technician A is wrong: MAF sensors have no replacement interval; they are replaced when testing shows a fault.
Correct: Technician B is right: a MAF sensor is replaced only after diagnosis confirms it is failed or out of calibration.
Incorrect: Replacing a good sensor on a schedule contradicts test-based replacement, so both cannot be right.
Incorrect: Technician B states the accepted practice, so rejecting both is wrong.
Question 13 of 14 · Engine Systems · 16%Not answered
During a visual inspection of a steel fuel tank, a technician notices an area of bubbled paint on the bottom of the tank. There is no active dripping. What is the most likely condition indicated by this finding?
Explanation
Incorrect: Factory paint on a steel tank is smooth; bubbles are not a normal texture.
Incorrect: A filler neck seal leak wets the neck area at the top of the tank, not the paint on the bottom.
Incorrect: Road debris impact leaves dents and scrapes, not bubbled paint.
Correct: Paint bubbling on a steel tank is lifted by rust forming underneath; the tank is then checked for thinning and leaks.
Incorrect: Loose mounting straps let the tank shift and rattle; they do not lift the paint.
Question 14 of 14 · Engine Systems · 16%Not answered
A vehicle has a rough idle and a hissing noise coming from the engine compartment. A technician visually inspects the PCV system. Which of the following findings is most likely causing the rough idle and hissing?
Explanation
Correct: A split PCV vacuum hose sits on the manifold-vacuum side, so it sucks in unmetered air with a hiss and leans out the idle.
Incorrect: The air inlet tube is not part of the PCV system being inspected, and at idle it sees little vacuum, so a loose clamp there barely hisses.
Incorrect: A saturated air filter restricts intake air at higher loads; it does not hiss or upset the idle.
Incorrect: A clogged PCV valve blocks crankcase flow, but it makes no hiss and has little effect on idle air.
Incorrect: The fresh-air breather hose carries filtered air at near-atmospheric pressure, so a loose one causes no hiss or rough idle.
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Pressure-test to the cap's rating
A cooling-system pressure test uses the pressure stamped on the radiator cap, not a multiple of it; more can split a hose or a plastic radiator tank. The guide's own sample question on this lists twice and three times the cap pressure as wrong answers. Test the cap itself too: a cap that won't hold its rating lowers the boiling point.
Where engine work becomes an A-test
Noises and leaks appear here at the check-and-report level. Measuring, tearing down and rebuilding is A1 Engine Repair; tracing a code, a misfire or an EVAP fault to its cause is A8 Engine Performance. On G1, the DTC task is to retrieve and record the code.