DFFT Cheat Sheet 2026

The 30 highest-yield DFFT facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. What might be the issue if there is excessive white smoke from the exhaust? → Burning coolant
2. What would happen if a vehicle is driven with mismatched tires — one radial and one bias-ply — on the same axle? → Unpredictable handling and uneven cornering forces due to different flex characteristics
3. What might cause the check engine light to come on? → Faulty oxygen sensor
4. A vehicle's parking brake fails to hold the car on a moderate hill. What is the most likely cause on a rear-drum brake vehicle? → Stretched or corroded parking brake cable
5. A water pump is removed and found to have eroded impeller vanes. What caused this condition? → Cavitation from low coolant levels or depleted coolant causing erosion of the impeller
6. What is the minimum legal tread depth for passenger car tires in the United States? → 2/32 inch
7. What is the most accurate way to determine whether a tire should be replaced due to age, even if tread depth is still acceptable? → Check the tire's DOT date code for manufacture date older than 6–10 years
8. Which issue might cause a grinding noise when shifting gears? → Worn clutch (manual transmission)
9. A vehicle's cooling system is pressurized to 16 psi and holds for 10 minutes, but the engine still overheats. What should be suspected? → A combustion gas leak into the coolant caused by a head gasket failure
10. A vehicle cranks but will not start in cold weather. The battery is fully charged. What should be checked on a fuel-injected gasoline engine? → Fuel pressure retention when the engine is cold and injector flow
11. A vehicle's battery goes flat overnight despite no obvious loads left on. What is this fault called? → Parasitic drain or key-off current draw
12. A diesel vehicle emits white smoke from the exhaust on startup that disappears when warm. What is the most likely cause? → Unburned diesel fuel from cylinders with a late injection timing or cold combustion
13. What does a scan tool reading of 0% on a fuel trim at wide open throttle (WOT) indicate? → The ECU has disabled fuel trim corrections at WOT, running from the base fuel map
14. If the engine's oil pressure warning light comes on, what should you check first? → Oil level
15. After bleeding the brakes, the pedal remains soft. What should the technician check next? → Inspect all brake hoses for internal collapse or restriction
16. A vehicle produces a whining noise that varies with engine speed when turning the steering wheel. What is the cause? → A low power steering fluid level causing the pump to cavitate
17. A vehicle's fuel economy has dropped significantly without any obvious drivability issues. What should be checked? → Oxygen sensor response time and catalytic converter efficiency
18. A catalytic converter is found to be glowing red hot during operation. What is the most likely cause? → Unburned fuel from engine misfires is igniting inside the converter
19. What is a common symptom of a failing transmission control module? → Inconsistent gear shifting
20. A vehicle's battery warning light stays on after starting the engine. What is the most likely cause? → The alternator is not charging the battery
21. A serpentine belt drives the water pump and alternator. What single symptom would indicate the belt has snapped? → Simultaneous battery warning light and rapid engine overheating
22. What might cause a burning smell from the transmission? → Overheated transmission fluid
23. If your car is leaking red or pink fluid, which component is most likely leaking? → Transmission
24. A high-pressure direct injection engine misfires intermittently under load. The low-pressure pump is fine. What should be tested? → The high-pressure fuel pump and fuel pressure at the injector rail
25. A vehicle has poor performance and black smoke from the exhaust. What does this indicate about the fuel mixture? → The engine is running excessively rich with too much fuel
26. A vehicle fails an emissions test for high HC (hydrocarbon) levels. What is the most likely cause? → Engine misfires causing unburned fuel to pass through the exhaust
27. A vehicle's ride height is lower on the driver's side than the passenger's side. What is the most likely cause? → A broken or sagged coil spring on the driver's side
28. A high-pitched squealing noise occurs whenever the brakes are lightly applied. What is the most likely cause? → Brake pad wear indicators contacting the rotor
29. A driver reports that the steering wheel shimmies (oscillates side to side) at around 45–55 mph but is smooth at other speeds. What is the most likely cause? → Static or dynamic wheel imbalance
30. A coolant temperature sensor is tested and reads 4.8V with the engine at normal operating temperature. Is this correct? → No, the sensor should read approximately 0.5–1.5V when hot, indicating low resistance