ASE Diesel Practice Test Graded A 2025

When a diesel engine is operated under a load, coolant continually comes out of the radiator overflow and there are bubbles in the radiator. Which of these is the most likely cause? (A) Too much coolant in the cooling system (B) A clogged radiator (C) A stuck-open thermostat (D) Compression leakage into the cooling system - Correct Answer-D A diesel engine has excessive black smoke when started in the morning. Which of these could be the cause? (A) A bad fuel injection nozzle (B) A restricted fuel filter (C) A blocked fuel tank vent (D) A leaking fuel return line - Correct Answer-A Which of these can cause a no-start condition on a HEUI engine? (A) High fuel pressure (B) Low injection control pressure (C) High boost pressure (D) Low boost pressure - Correct Answer-B A diesel engine is hard to start, but runs good after it has been primed and run for a few minutes. The most likely cause is a: (A) leaking injector line. (B) leaking fuel return line. (C) plugged fuel tank vent. (D) bad transfer pump check valve. - Correct Answer-D A diesel engine with wet liners has been running too hot, and there is coolant in the crankcase. The most likely cause is: (A) a cracked block. (B) cracked liners. (C) leaking liner seals. (D) a leaking injector seal. - Correct Answer-C Diesel engine cylinder liner protrusion (height) can be adjusted by selecting the correct size: (A) cylinder liner. (B) head gasket. (C) liner shim. (D) fire ring. - Correct Answer-C An electronically-controlled diesel engine will not start. Any of these could be the cause EXCEPT a failed: (A) camshaft position sensor. (B) engine control module (ECM). (C) ECM ground circuit. (D) throttle position sensor (TPS). - Correct Answer-D The cause of a logged fault code in an electronic diesel engine has just been repaired. Technician A says that the codes should be cleared before releasing the vehicle. Technician B says that the customer's password should be reset before releasing the vehicle. Who is right? (A) A only (C) Both A and B (B) B only (D) Neither A nor B - Correct Answer-A A diesel engine has low power and low turbocharger boost pressure is found. Technician A says that a leaking exhaust manifold could be the cause. Technician B says that a plugged turbocharger oil return line could be the cause. Who is right? (A) A only (B) B only (C) Both A and B (D) Neither A nor B - Correct Answer-A The parking brakes fail to apply on a truck with air brakes. Technician A says that low air pressure in the spring brake chamber could be the cause. Technician B says that a ruptured spring brake diaphragm could be the cause. Who is right? (A) A only (B) B only (C) Both A and B (D) Neither A nor B - Correct Answer-D A truck equipped with air brakes has an uneven braking problem. Which of these could be the cause? (A) A binding treadle (foot) valve (B) Low brake line air pressure (C) A bad brake drum (D) A bad governor - Correct Answer-C A service brake on a truck with an air brake system releases too slowly. Technician A says that low air pressure could be the cause. Technician B says that a kinked air line could be the cause. Who is right? (A) A only (C) Both A and B (B) B only (D) Neither A nor B - Correct Answer-B A service brake chamber leaks when the brakes are applied. Which of these could be the cause? (A) Excessive push rod travel (B) A bad chamber diaphragm (C) A broken chamber return spring (D) A misaligned push rod - Correct Answer-B All the wheels on a truck with air brakes lock up when a small amount of pressure is applied to the treadle (foot) valve. Which of these could be the cause? (A) The application valve is bad. (B) The limiting valve is leaking. (C) The compressor regulator is set too high. (D) The brakes are adjusted too high. - Correct Answer-A When an air reservoir tank is drained, there is an excessive amount of moisture. This could be caused by a: (A) cracked air compressor bracket. (B) clogged air compressor intake. (C) failed one way check valve. (D) failed air dryer purge valve. - Correct Answer-D All the brakes drag on a truck with hydraulic brakes. Which of these could be the cause? (A) Air in the hydraulic system (B) Too high vacuum supply to the power brake booster (C) A leaking secondary cup in the master cylinder (D) No brake pedal free travel - Correct Answer-D A truck with hydraulic brakes pulls to one side when the brakes are applied. Any of these could be the cause EXCEPT a: (A) sticking wheel cylinder piston. (B) grease contaminated brake lining. (C) crimped hydraulic line. (D) plugged compensating port. - Correct Answer-D The driver of a truck with air brakes says it has poor stopping power. Any of these could be the cause EXCEPT: (A) the quick release valve exhaust port is plugged. (B) the air pressure is too low. (C) the application line is restricted. (D) the brakes are out of adjustment - Correct Answer-A Which of these could cause the front tires of a truck to show a feathered edge wear pattern? (A) An incorrect toe setting (B) An incorrect camber setting (C) An incorrect caster setting (D) Incorrect tire pressures - Correct Answer-A The drive axles on a truck with a walking beam suspension are out of alignment. Technician A says that incorrect length torque rods could be the cause. Technician B says that worn walking beam bushings could be the cause. Who is right? (A) A only (C) Both A and B (B) B only (D) Neither A nor B - Correct Answer-B The driver of a truck that has just had its front springs and hangers replaced says that it is hard to keep in a straight ahead position. Technician A says that this could be caused by installing the caster shims backwards. Technician B says that this could be caused by installing forward spring hangers which are too short. Who is right? (A) A only (C) Both A and B (B) B only (D) Neither A nor B - Correct Answer-A The driver of a truck says that it is hard to steer and the steering wheel return is poor. Technician A says that binding kingpins could be the cause. Technician B says that too much toe-in could be the cause. Who is right? (A) A only (C) Both A and B (B) B only (D) Neither A nor B - Correct Answer-A Rust streaks coming from around the stud holes of a disc wheel could be caused by: (A) an overloaded conditon. (B) overtorqued lug/cap nuts. (C) an out-of-balance condition. (D) loose lug/cap nuts. - Correct Answe