• 50 questions

ASE L1 Test Prep

Unofficial advanced engine performance practice in the six content areas of ASE's L1 test specifications, every answer with its source.

Which fault can a cranking compression test show that a static leak-down test will not?

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Exam mode: 50 questions, 150 minutes.

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Unofficial practice questions, not affiliated with the National Institute for Automotive Service Excellence (ASE). Bank checked October 8, 2026.

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All 50 questions

General powertrain diagnosis 6

  • A cam phaser is stuck in one position. What does a cam-phasing system change when it works? Wikipedia, Variable valve timing, section Cam phasing versus variable duration. ASE L1 content area A, General Powertrain Diagnosis (6 of 50 questions)
  • A fuel-injected engine has a driveability fault and no stored codes. Which order of diagnosis does the Navy manual advise? U.S. Navy, Construction Mechanic Advanced (NAVEDTRA 14050, 1992), chapter 5, Servicing and Precautions. ASE L1 content area A, General Powertrain Diagnosis (6 of 50 questions)
  • A replacement catalytic converter has overheated and failed for the second time. Which root cause should be looked for first? Wikipedia, Catalytic converter, section Damage. ASE L1 content area A, General Powertrain Diagnosis (6 of 50 questions)
  • A vehicle fails for HC and uses too much fuel. On a long drive, scan data shows coolant temperature leveling off far below normal. Which part is the root cause? U.S. Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 8-4c, Oil Dilution, and paragraph 9-9, Thermostats. ASE L1 content area A, General Powertrain Diagnosis (6 of 50 questions)
  • One cylinder misfires with good spark and good injector pulse. With shop air in that cylinder at TDC on compression, a hiss is heard at the tailpipe. What is the fault? Wikipedia, Leak-down tester, opening section. ASE L1 content area A, General Powertrain Diagnosis (6 of 50 questions)
  • Which fault can a cranking compression test show that a static leak-down test will not? Wikipedia, Leak-down tester, opening section. ASE L1 content area A, General Powertrain Diagnosis (6 of 50 questions)
Show all 50 questions (44 more)

Computerized controls and OBD II 16

  • A fault is repaired on a 2010 vehicle and the codes are left in memory. When may the OBD II system turn the MIL off by itself? California Code of Regulations, title 13, section 1968.2 (OBD II), section (d)(2.3.1). ASE L1 content area B, Computerized Powertrain Controls Diagnosis, including OBD II (16 of 50)
  • A pending code is stored. The same malfunction is detected again before the end of the next driving cycle in which the monitor runs. What happens? California Code of Regulations, title 13, section 1968.2 (OBD II), section (d)(2.2.2). ASE L1 content area B, Computerized Powertrain Controls Diagnosis, including OBD II (16 of 50)
  • A thermistor-type coolant temperature sensor is fed a reference voltage by the control unit. What does the control unit read to learn the temperature? U.S. Navy, Construction Mechanic Advanced (NAVEDTRA 14050, 1992), chapter 4, Computerized Ignition System, Coolant Temperature Sensor. ASE L1 content area B, Computerized Powertrain Controls Diagnosis, including OBD II (16 of 50)
  • A voltmeter is connected across the ground side of a circuit while it carries current. The reading is well above 0.2 volt. What does this indicate? U.S. Navy, Construction Mechanic Advanced (NAVEDTRA 14050, 1992), chapter 4, Starter Ground Circuit Resistance Test. ASE L1 content area B, Computerized Powertrain Controls Diagnosis, including OBD II (16 of 50)
  • After a battery replacement, several readiness indicators read incomplete. What does that mean? California Air Resources Board, OBD II Systems Fact Sheet, How is Smog Check affected by OBD II?. ASE L1 content area B, Computerized Powertrain Controls Diagnosis, including OBD II (16 of 50)
  • After a replacement key is cut, the engine cranks normally but will not start: no injector pulse and no spark. Which system is checked first? Wikipedia, Immobiliser, section Description. ASE L1 content area B, Computerized Powertrain Controls Diagnosis, including OBD II (16 of 50)
  • An engine cuts out while running, then cranks without starting, and the scan tool shows no engine speed while cranking. Which sensor fits? Wikipedia, Crankshaft position sensor, opening section. ASE L1 content area B, Computerized Powertrain Controls Diagnosis, including OBD II (16 of 50)
  • An OBD II monitor detects a malfunction for the first time. What is stored? California Code of Regulations, title 13, section 1968.2 (OBD II), section (d)(2.2.1). ASE L1 content area B, Computerized Powertrain Controls Diagnosis, including OBD II (16 of 50)
  • Before a control unit is reprogrammed, which OBD II item identifies the software calibration it holds now? California Code of Regulations, title 13, section 1968.2 (OBD II), section (g)(4.6.1). ASE L1 content area B, Computerized Powertrain Controls Diagnosis, including OBD II (16 of 50)
  • Codes are cleared with a scan tool, but a permanent fault code is still reported. How does it get erased? California Code of Regulations, title 13, section 1968.2 (OBD II), section (d)(2.5.2). ASE L1 content area B, Computerized Powertrain Controls Diagnosis, including OBD II (16 of 50)
  • Long-term fuel trim on bank 1 reads plus 18 percent. What is the control unit doing? Wikipedia, OBD-II PIDs, Service 01, PIDs 06 to 09 (fuel trim). ASE L1 content area B, Computerized Powertrain Controls Diagnosis, including OBD II (16 of 50)
  • The MIL has gone out by itself on a 2010 vehicle. When may the system erase the confirmed fault code? California Code of Regulations, title 13, section 1968.2 (OBD II), section (d)(2.4). ASE L1 content area B, Computerized Powertrain Controls Diagnosis, including OBD II (16 of 50)
  • On a gasoline engine, what makes a driving cycle count as a warm-up cycle? California Code of Regulations, title 13, section 1968.2 (OBD II), section (c), definition of warm-up cycle. ASE L1 content area B, Computerized Powertrain Controls Diagnosis, including OBD II (16 of 50)
  • Under load the MIL blinks about once per second, then stays lit when the load eases. What is the system reporting? California Code of Regulations, title 13, section 1968.2 (OBD II), section (e)(3.4.1)(A)(ii). ASE L1 content area B, Computerized Powertrain Controls Diagnosis, including OBD II (16 of 50)
  • What does freeze frame data show? California Code of Regulations, title 13, section 1968.2 (OBD II), section (d)(2.2.7). ASE L1 content area B, Computerized Powertrain Controls Diagnosis, including OBD II (16 of 50)
  • Where are the terminating resistors of a high-speed CAN bus, and what is their value? Wikipedia, CAN bus, section on the ISO 11898-2 physical layer. ASE L1 content area B, Computerized Powertrain Controls Diagnosis, including OBD II (16 of 50)

Ignition system 6

  • A knock sensor reports the pressure peak of knocking combustion. How does the control unit respond? Wikipedia, Engine knocking, section on knock control. ASE L1 content area C, Ignition System Diagnosis (6 of 50)
  • A set of spark plugs has worn until the gaps are too wide. What is the most likely result? Wikipedia, Spark plug, section on the spark plug gap. ASE L1 content area C, Ignition System Diagnosis (6 of 50)
  • At what moment does an ignition coil produce its high secondary voltage? U.S. Navy, Construction Mechanic Advanced (NAVEDTRA 14050, 1992), chapter 4, Electronic ignition systems. ASE L1 content area C, Ignition System Diagnosis (6 of 50)
  • In a waste-spark ignition system, which two cylinders share one coil firing? Wikipedia, Wasted spark system, opening section. ASE L1 content area C, Ignition System Diagnosis (6 of 50)
  • The spark occurs too far advanced for the piston position. What is the result? Wikipedia, Ignition timing, section on setting the ignition timing. ASE L1 content area C, Ignition System Diagnosis (6 of 50)
  • Which mixtures does a longer spark duration help most to fire? U.S. Navy, Construction Mechanic Advanced (NAVEDTRA 14050, 1992), chapter 4, High-Energy Ignition System. ASE L1 content area C, Ignition System Diagnosis (6 of 50)

Fuel and air induction 8

  • A fuel blend with more oxygenate has a lower stoichiometric ratio than plain gasoline. How does a closed-loop engine respond? Wikipedia, Air–fuel ratio, section on other fuels and oxygenates. ASE L1 content area D, Fuel Systems and Air Induction Systems Diagnosis (8 of 50)
  • A narrowband zirconia oxygen sensor holds near 0.8 volt. What is it reporting? Wikipedia, Oxygen sensor, section on the zirconia sensor. ASE L1 content area D, Fuel Systems and Air Induction Systems Diagnosis (8 of 50)
  • A speed-density system has no mass airflow sensor. Which inputs does it use to work out air mass? Wikipedia, MAP sensor, opening section. ASE L1 content area D, Fuel Systems and Air Induction Systems Diagnosis (8 of 50)
  • After a fault, the control unit shuts off the signal to the throttle motor (limp-home mode). What happens to the throttle? Wikipedia, Electronic throttle control, section on limp-home mode. ASE L1 content area D, Fuel Systems and Air Induction Systems Diagnosis (8 of 50)
  • An oiled-gauze air filter was fitted and over-oiled. Which sensor can it throw off? Wikipedia, Mass flow sensor, section on the hot wire sensor. ASE L1 content area D, Fuel Systems and Air Induction Systems Diagnosis (8 of 50)
  • By mass, which of these air-fuel ratios is lean for gasoline? Wikipedia, Air–fuel ratio, section on the stoichiometric mixture. ASE L1 content area D, Fuel Systems and Air Induction Systems Diagnosis (8 of 50)
  • On a gasoline direct injection engine, where is the high-pressure fuel pump? Wikipedia, Fuel pump, opening section. ASE L1 content area D, Fuel Systems and Air Induction Systems Diagnosis (8 of 50)
  • Which describes the accelerator pedal module of a typical electronic throttle control system? Wikipedia, Electronic throttle control, section Operation. ASE L1 content area D, Fuel Systems and Air Induction Systems Diagnosis (8 of 50)

Emission control systems 8

  • Carbon holds an EGR valve partly open at all times. When is the symptom worst? Wikipedia, Exhaust gas recirculation, section on spark-ignition engines. ASE L1 content area E, Emission Control Systems Diagnosis (8 of 50)
  • How does exhaust gas recirculation lower NOx? U.S. Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 7-10a, Exhaust Gas Recirculation System. ASE L1 content area E, Emission Control Systems Diagnosis (8 of 50)
  • How does the on-board system judge catalytic converter efficiency? Wikipedia, Oxygen sensor, section on automotive applications. ASE L1 content area E, Emission Control Systems Diagnosis (8 of 50)
  • Under what fuel control does a three-way catalytic converter work best? Wikipedia, Catalytic converter, section on the three-way converter. ASE L1 content area E, Emission Control Systems Diagnosis (8 of 50)
  • What does the onboard refueling vapor recovery (ORVR) system do with vapors pushed out of the tank during a fill-up? Wikipedia, Onboard refueling vapor recovery, section Problem. ASE L1 content area E, Emission Control Systems Diagnosis (8 of 50)
  • What is the smallest evaporative system leak that the OBD II regulation names for leak detection? California Code of Regulations, title 13, section 1968.2 (OBD II), section (d)(3.2.1)(B). ASE L1 content area E, Emission Control Systems Diagnosis (8 of 50)
  • Which sensor can an OBD II system use to test the EGR valve for function? Wikipedia, MAP sensor, opening section. ASE L1 content area E, Emission Control Systems Diagnosis (8 of 50)
  • Why does a secondary air system inject air at the upstream point while the converter is cold? Wikipedia, Secondary air injection, section on air injection with catalytic converters. ASE L1 content area E, Emission Control Systems Diagnosis (8 of 50)

I/M failure diagnosis 6

  • A 2012 vehicle comes to an OBD I/M test with no MIL command. How many unset readiness monitors does the federal procedure allow it and still pass? 40 CFR 85.2222, paragraph (c)(2). ASE L1 content area F, I/M Failure Diagnosis (6 of 50)
  • A vehicle fails a loaded-mode test for CO. What condition forms CO? U.S. Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 7-5a, Carbon Monoxide. ASE L1 content area F, I/M Failure Diagnosis (6 of 50)
  • A vehicle fails a loaded-mode test for NOx. What forms NOx in the cylinder? U.S. Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 7-10a, Exhaust Gas Recirculation System. ASE L1 content area F, I/M Failure Diagnosis (6 of 50)
  • A vehicle fails a tailpipe test for HC. What is HC on the test slip? Wikipedia, Exhaust gas, opening section. ASE L1 content area F, I/M Failure Diagnosis (6 of 50)
  • During an OBD I/M inspection the MIL is not commanded on, but stored DTCs are found. What is the result under the federal test procedure? 40 CFR 85.2222, paragraph (d)(2). ASE L1 content area F, I/M Failure Diagnosis (6 of 50)
  • With the key on and the engine off, the MIL does not light at all. No DTCs are stored. What is the OBD inspection result? 40 CFR 85.2222, paragraph (d)(4). ASE L1 content area F, I/M Failure Diagnosis (6 of 50)

How this list was compiled: Our own questions, written to the test specifications for the Advanced Engine Performance Specialist (L1) Test in ASE's L1 study guide (https://ase.com/wp-content/uploads/ASE_L1_Study_Guide.pdf, marked (c) ASE 2026, read 2026-10-08): A general powertrain diagnosis 6 questions, B computerized powertrain controls diagnosis (including OBD II) 16, C ignition system diagnosis 6, D fuel systems and air induction systems diagnosis 8, E emission control systems diagnosis 8, F I/M failure diagnosis 6; total 50. The bank holds the same 6, 16, 6, 8, 8 and 6. Each fact was read on 2026-10-08 in the public source named under its question: California's OBD II regulation (13 CCR 1968.2, read in the public copy at law.cornell.edu), the Air Resources Board's OBD II fact sheet, EPA's OBD inspection procedure (40 CFR 85.2222), the U.S. Army manual TM 9-8000, the U.S. Navy manual NAVEDTRA 14050 and Wikipedia. No question uses ASE's composite vehicle reference booklet. Licence: Questions, choices and explanations are original work of this site.

How it works

This free ASE L1 test prep is a practice test: 50 advanced engine performance questions of our own, weighted like the real test. It is unofficial and not affiliated with, endorsed by or sponsored by the National Institute for Automotive Service Excellence (ASE).

Read the full guide

What the L1 test covers

ASE's study guide splits the 50 scored questions: general powertrain diagnosis 6, computerized powertrain controls including OBD II 16, ignition 6, fuel and air induction 8, emission control systems 8, and I/M failure diagnosis 6. This bank holds the same counts.

Length and timing

Exam mode asks 50 questions, the scored count, in the real test's 150 minutes.

The composite vehicle

Many real questions use ASE's Composite Vehicle Type 4 reference, shown as a pop-up during the test. Read that booklet as well: these questions carry their own readings and do not use it.

  • Computerized controls and OBD II are the largest area, 16 of 50. Learn when a code is pending, confirmed or permanent.
  • For I/M failures, tie each gas to its cause first: HC to unburned fuel, CO to a rich mixture, NOx to combustion heat.

Questions and answers

How many questions are on the ASE L1 test?

ASE's study guide lists 60 questions, 50 of them scored, in 2.5 hours. The recertification test (L1R) is 50 questions in 2.25 hours. You are not told which 10 are unscored, so answer every one.

What do you need before taking the ASE test L1?

A pass on the Automobile Engine Performance (A8) test: ASE will not let you register for L1 without it. Certification also needs three years of documented work experience, and vocational training may count toward part of it.

Is there an ASE L1 study guide?

Yes, free from ASE: the L1 study guide holds the test specifications and task list this page follows, and a separate booklet describes the composite vehicle. Our questions are our own and are not taken from either.

Can I get an ASE L1 practice test PDF?

Not as a download. Print, on the score card after a round, lays the questions out for paper, with the key if you tick With answer key, and your browser's print window can save that as a PDF.

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