ASE A9 Practice Test

2025 Edition

ASE identifies Light Vehicle Diesel Engines as an individual service area (A9). The light vehicle diesel engine area involves the following diagnosis components:

• Cylinder Head and Valve Train
• Engine Block
• Lubrication and Cooling Systems
• Air Induction and Exhaust Systems
• Fuel Systems

Tests.com's ASE A9 Practice Test was written by Dr. John Kershaw, an ASE test prep expert: ASE test question developer; ASE Certified Master Technician; ASE Master Truck Technician; and Auto Industry Technical Instructor. Dr. Kershaw was among the first to receive ASE certification in 1972.

For the complete practice test, flash cards, exam review and testing tips, check out Tests.com's ASE A9 practice test kit with 130 questions.

General Diagnosis

1.	Which diagnostic tool connects to the Data Link Connector and allows the technician to read light duty diesel engine diagnostic trouble codes?
		a. DMM (Digital Multimeter)
Both b and c are correct because since OBD II (On-Board Diagnostic Level II), the industry has used a 5 character diagnostic trouble code that can only be read with another computer like a scan tool or PC based laptop computer. Incorrect answer. Please choose another answer.
		b. Diagnostic Scan Tool
Both b and c are correct because since OBD II (On-Board Diagnostic Level II), the industry has used a 5 character diagnostic trouble code that can only be read with another computer like a scan tool or PC based laptop computer. Incorrect answer. Please choose another answer.
		c. Laptop computer with interface
Both b and c are correct because since OBD II (On-Board Diagnostic Level II), the industry has used a 5 character diagnostic trouble code that can only be read with another computer like a scan tool or PC based laptop computer. Incorrect answer. Please choose another answer.
		d. Both b and c
Both b and c are correct because since OBD II (On-Board Diagnostic Level II), the industry has used a 5 character diagnostic trouble code that can only be read with another computer like a scan tool or PC based laptop computer. Incorrect answer. Please choose another answer.

General Diagnosis

2.	An orange colored liquid is found under the front of the engine, which of the following fluids is leaking?
		a. Engine Oil
Coolant is orange, pink or green. Engine oil is yellow or brown. ATF is red. Washer fluid is blue. Incorrect answer. Please choose another answer.
		b. Coolant
Coolant is orange, pink or green. Engine oil is yellow or brown. ATF is red. Washer fluid is blue. Incorrect answer. Please choose another answer.
		c. ATF
Coolant is orange, pink or green. Engine oil is yellow or brown. ATF is red. Washer fluid is blue. Incorrect answer. Please choose another answer.
		d. Washer Fluid
Coolant is orange, pink or green. Engine oil is yellow or brown. ATF is red. Washer fluid is blue. Incorrect answer. Please choose another answer.

Cylinder Head and Valve Train Diagnosis and Repair

3.	Two technicians are discussing engine valve seals. Technician A says to apply a light coat of engine oil to new oil seals and push them in. Technician B says you can install the intake oil seal into the exhaust side or install the exhaust oil seal into the intake side because they are interchangeable. Who is right?
		a. A only
Tech A is right because you need to apply a light coat of engine oil to new oil seals to help ease them in. Tech B is wrong because installing the intake oil seal into the exhaust side or installing the exhaust oil seal into the intake side can cause problems later because the exhaust side is generally hotter than the intake side and the seals are generally different and made of different material and therefore not interchangeable. Incorrect answer. Please choose another answer.
		b. B only
Tech A is right because you need to apply a light coat of engine oil to new oil seals to help ease them in. Tech B is wrong because installing the intake oil seal into the exhaust side or installing the exhaust oil seal into the intake side can cause problems later because the exhaust side is generally hotter than the intake side and the seals are generally different and made of different material and therefore not interchangeable. Incorrect answer. Please choose another answer.
		c. Both A and B
Tech A is right because you need to apply a light coat of engine oil to new oil seals to help ease them in. Tech B is wrong because installing the intake oil seal into the exhaust side or installing the exhaust oil seal into the intake side can cause problems later because the exhaust side is generally hotter than the intake side and the seals are generally different and made of different material and therefore not interchangeable. Incorrect answer. Please choose another answer.
		d. Neither A nor B
Tech A is right because you need to apply a light coat of engine oil to new oil seals to help ease them in. Tech B is wrong because installing the intake oil seal into the exhaust side or installing the exhaust oil seal into the intake side can cause problems later because the exhaust side is generally hotter than the intake side and the seals are generally different and made of different material and therefore not interchangeable. Incorrect answer. Please choose another answer.

Cylinder Head and Valve Train Diagnosis and Repair

4.	Valve adjustment is necessary following the replacement of a:
		a. Crankshaft
Valve adjustment is necessary following the replacement of any valve train or cylinder head. Incorrect answer. Please choose another answer.
		b. Piston
Valve adjustment is necessary following the replacement of any valve train or cylinder head. Incorrect answer. Please choose another answer.
		c. Balancer
Valve adjustment is necessary following the replacement of any valve train or cylinder head. Incorrect answer. Please choose another answer.
		d. Cylinder head
Valve adjustment is necessary following the replacement of any valve train or cylinder head. Incorrect answer. Please choose another answer.

Engine Block Diagnosis and Repair

5.	After cleaning a diesel block and crankshaft, what chemical should they be sprayed with?
		a. Rust inhibitor
Spraying the block with a rust inhibiter and wrapping the engine with a plastic bag keeps the engine free from corrosion until you are ready to assemble it.. The other chemicals are not as effective. Incorrect answer. Please choose another answer.
		b. Engine oil
Spraying the block with a rust inhibiter and wrapping the engine with a plastic bag keeps the engine free from corrosion until you are ready to assemble it.. The other chemicals are not as effective. Incorrect answer. Please choose another answer.
		c. Anti-seize compound
Spraying the block with a rust inhibiter and wrapping the engine with a plastic bag keeps the engine free from corrosion until you are ready to assemble it.. The other chemicals are not as effective. Incorrect answer. Please choose another answer.
		d. Assembly lube
Spraying the block with a rust inhibiter and wrapping the engine with a plastic bag keeps the engine free from corrosion until you are ready to assemble it.. The other chemicals are not as effective. Incorrect answer. Please choose another answer.

ASE A9 Practice Test

General Diagnosis

General Diagnosis

Cylinder Head and Valve Train Diagnosis and Repair

Cylinder Head and Valve Train Diagnosis and Repair

Engine Block Diagnosis and Repair

Engine Block Diagnosis and Repair

Lubrication and Cooling Systems Diagnosis and Repair

Lubrication and Cooling Systems Diagnosis and Repair

Air Induction and Exhaust Systems Diagnosis and Repair

Air Induction and Exhaust Systems Diagnosis and Repair

Fuel Systems Diagnosis and Repair

Fuel Systems Diagnosis and Repair

Engine Block Diagnosis and Repair

6.	When measuring a cylinder for taper wear, which of the following is the MOST likely place for wear?
		a. Middle of cylinder
The top of the cylinder is where the maximum temperature is found. Incorrect answer. Please choose another answer.
		b. Bottom of cylinder
The top of the cylinder is where the maximum temperature is found. Incorrect answer. Please choose another answer.
		c. At a right angle to top
The top of the cylinder is where the maximum temperature is found. Incorrect answer. Please choose another answer.
		d. Top of cylinder
The top of the cylinder is where the maximum temperature is found. Incorrect answer. Please choose another answer.

Lubrication and Cooling Systems Diagnosis and Repair

7.	Technician A says a weak solution of antifreeze may cause corrosion build-up in the cooling system. Technician B says engine coolants and rust inhibitors last the lifetime of the diesel engine. Who is right?
		a. A only
Tech A is right because a weak solution of antifreeze may cause corrosion build-up in the cooling system. Tech B is wrong because most original equipment manufacturers (OEM) recommend that the coolant be changed at specified intervals due to a loss in corrosion inhibitor life. Incorrect answer. Please choose another answer.
		b. B only
Tech A is right because a weak solution of antifreeze may cause corrosion build-up in the cooling system. Tech B is wrong because most original equipment manufacturers (OEM) recommend that the coolant be changed at specified intervals due to a loss in corrosion inhibitor life. Incorrect answer. Please choose another answer.
		c. Both A and B
Tech A is right because a weak solution of antifreeze may cause corrosion build-up in the cooling system. Tech B is wrong because most original equipment manufacturers (OEM) recommend that the coolant be changed at specified intervals due to a loss in corrosion inhibitor life. Incorrect answer. Please choose another answer.
		d. Neither A nor B
Tech A is right because a weak solution of antifreeze may cause corrosion build-up in the cooling system. Tech B is wrong because most original equipment manufacturers (OEM) recommend that the coolant be changed at specified intervals due to a loss in corrosion inhibitor life. Incorrect answer. Please choose another answer.

Lubrication and Cooling Systems Diagnosis and Repair

8.	This question has the word EXCEPT. For this question, look for the choice that would NOT fit the described situation. Read the entire question carefully before choosing your answer. All of the following will happen when an oil filter becomes clogged, EXCEPT:
		a. Bypass valve allows dirty oil to lubricate the engine.
The oil pump will slow down not speed up when an oil filter becomes clogged. A, b and c will occur when an oil filter becomes clogged. Incorrect answer. Please choose another answer.
		b. Oil pump must slow down.
The oil pump will slow down not speed up when an oil filter becomes clogged. A, b and c will occur when an oil filter becomes clogged. Incorrect answer. Please choose another answer.
		c. Engine operating temperature increases.
The oil pump will slow down not speed up when an oil filter becomes clogged. A, b and c will occur when an oil filter becomes clogged. Incorrect answer. Please choose another answer.
		d. Oil pump must speed up.
The oil pump will slow down not speed up when an oil filter becomes clogged. A, b and c will occur when an oil filter becomes clogged. Incorrect answer. Please choose another answer.

Air Induction and Exhaust Systems Diagnosis and Repair

9.	A light duty diesel engine has a sever oil leak at the rocker cover. The technician has replaced the rocker cover gasket but the gasket still leaks. Which of the following is the MOST likely cause?
		a. Defective cylinder head
This is the MOST likely cause of the 4 choices. The CDR (crankcase depression regulator) is designed to depress or reduce the crankcase pressure. If it is stuck closed, the pressure in the crankcase increases and pushes the oil out. Incorrect answer. Please choose another answer.
		b. Defective CDR (crankcase depression regulator) valve
This is the MOST likely cause of the 4 choices. The CDR (crankcase depression regulator) is designed to depress or reduce the crankcase pressure. If it is stuck closed, the pressure in the crankcase increases and pushes the oil out. Incorrect answer. Please choose another answer.
		c. Wrong gasket
This is the MOST likely cause of the 4 choices. The CDR (crankcase depression regulator) is designed to depress or reduce the crankcase pressure. If it is stuck closed, the pressure in the crankcase increases and pushes the oil out. Incorrect answer. Please choose another answer.
		d. Not enough sealer used
This is the MOST likely cause of the 4 choices. The CDR (crankcase depression regulator) is designed to depress or reduce the crankcase pressure. If it is stuck closed, the pressure in the crankcase increases and pushes the oil out. Incorrect answer. Please choose another answer.

Air Induction and Exhaust Systems Diagnosis and Repair

10.	A Catalyzed DPF (Diesel Particulate Filter) requires oil with which of the following characteristics?
		a. 0% Sulphur
Ash is mostly material left over after oil is burned in the combustion chamber. Ash must be physically removed from a DPF since it cannot be regenerated. The other choices do not apply to a DPF. Incorrect answer. Please choose another answer.
		b. High viscosity index
Ash is mostly material left over after oil is burned in the combustion chamber. Ash must be physically removed from a DPF since it cannot be regenerated. The other choices do not apply to a DPF. Incorrect answer. Please choose another answer.
		c. Low ash content
Ash is mostly material left over after oil is burned in the combustion chamber. Ash must be physically removed from a DPF since it cannot be regenerated. The other choices do not apply to a DPF. Incorrect answer. Please choose another answer.
		d. High alkalinity
Ash is mostly material left over after oil is burned in the combustion chamber. Ash must be physically removed from a DPF since it cannot be regenerated. The other choices do not apply to a DPF. Incorrect answer. Please choose another answer.

Fuel Systems Diagnosis and Repair

11.	A diesel engine with an electronically managed solenoid pump and nozzles has an active diagnostic trouble code for a single cylinder #3 misfire with a rough idle at operating temperature. Which of the following actions could cause the problem?
		a. Wrong line on cylinder
A short or long replacement line that is different than the original will change the timing in the number 3 cylinder and cause a rough idle or misfire. B is wrong because a glow plug failure does not cause a misfire or rough idle on an engine when hot. C is wrong because a glow plug failure does not cause a misfire or rough idle on an engine when hot. D is wrong because high Cetane fuel does not cause a misfire. High Cetane numbers indicate good ignition quality resulting in a short delay period and low Cetane numbers indicate poor ignition quality that results in a long delay period. Low Cetane numbers can cause a long ignition delay, which can cause a hard starting with white smoke and misfiring cylinders. Incorrect answer. Please choose another answer.
		b. Open cylinder glow plug
A short or long replacement line that is different than the original will change the timing in the number 3 cylinder and cause a rough idle or misfire. B is wrong because a glow plug failure does not cause a misfire or rough idle on an engine when hot. C is wrong because a glow plug failure does not cause a misfire or rough idle on an engine when hot. D is wrong because high Cetane fuel does not cause a misfire. High Cetane numbers indicate good ignition quality resulting in a short delay period and low Cetane numbers indicate poor ignition quality that results in a long delay period. Low Cetane numbers can cause a long ignition delay, which can cause a hard starting with white smoke and misfiring cylinders. Incorrect answer. Please choose another answer.
		c. Shorted cylinder glow plug
A short or long replacement line that is different than the original will change the timing in the number 3 cylinder and cause a rough idle or misfire. B is wrong because a glow plug failure does not cause a misfire or rough idle on an engine when hot. C is wrong because a glow plug failure does not cause a misfire or rough idle on an engine when hot. D is wrong because high Cetane fuel does not cause a misfire. High Cetane numbers indicate good ignition quality resulting in a short delay period and low Cetane numbers indicate poor ignition quality that results in a long delay period. Low Cetane numbers can cause a long ignition delay, which can cause a hard starting with white smoke and misfiring cylinders. Incorrect answer. Please choose another answer.
		d. High Cetane fuel rating
A short or long replacement line that is different than the original will change the timing in the number 3 cylinder and cause a rough idle or misfire. B is wrong because a glow plug failure does not cause a misfire or rough idle on an engine when hot. C is wrong because a glow plug failure does not cause a misfire or rough idle on an engine when hot. D is wrong because high Cetane fuel does not cause a misfire. High Cetane numbers indicate good ignition quality resulting in a short delay period and low Cetane numbers indicate poor ignition quality that results in a long delay period. Low Cetane numbers can cause a long ignition delay, which can cause a hard starting with white smoke and misfiring cylinders. Incorrect answer. Please choose another answer.

Fuel Systems Diagnosis and Repair

12.	The primary fuel system supply side vacuum test should be performed at which area:
		a. The outlet pipe for the high-pressure pump looking back to the filter
The intake pipe of the high pressure pump is where the pump will have lowest pressure. A is wrong because positive pressure would be present at the outlet pipe. B is wrong because positive pressure would be present at the inlet of the secondary air filter. D is wrong because positive pressure would be present at the inlet side of the primary filter. Incorrect answer. Please choose another answer.
		b. At inlet of the secondary filter looking at the tank
The intake pipe of the high pressure pump is where the pump will have lowest pressure. A is wrong because positive pressure would be present at the outlet pipe. B is wrong because positive pressure would be present at the inlet of the secondary air filter. D is wrong because positive pressure would be present at the inlet side of the primary filter. Incorrect answer. Please choose another answer.
		c. At the intake pipe for the high-pressure pump, looking at pump
The intake pipe of the high pressure pump is where the pump will have lowest pressure. A is wrong because positive pressure would be present at the outlet pipe. B is wrong because positive pressure would be present at the inlet of the secondary air filter. D is wrong because positive pressure would be present at the inlet side of the primary filter. Incorrect answer. Please choose another answer.
		d. At the inlet side of the primary filter looking at the tank
The intake pipe of the high pressure pump is where the pump will have lowest pressure. A is wrong because positive pressure would be present at the outlet pipe. B is wrong because positive pressure would be present at the inlet of the secondary air filter. D is wrong because positive pressure would be present at the inlet side of the primary filter. Incorrect answer. Please choose another answer.