ASE L1 Advanced Engine Performance Q&A Part 2

ASE Practice Test Questions & Answers with Explanation

1. The composite vehicle fails an I/M 240 test due to high carbon monoxide emissions. HC is barely within limits, while NOx is well below the maximum cut-point. Once the cause of the high CO has been corrected, the vehicle is retested and fails again, only this time for excessive NOx. What is the MOST likely reason for the subsequent failure?
A. The converter was damaged as a result of the CO failure.
B. The CO failure masked the NOx problem.
C. The technician damaged the EGR vacuum line while making the initial repair.
D. The failed retest was coincidental.
The correct answer is B The situation described in this question is not unusual. High CO emissions are always the result of a rich mixture, which is the reason for the composite vehicle’s initial failure. However, because a rich mixture lowers combustion temperatures, a CO failure can mask an underlying NOx problem. This is why the NOx problem became apparent only after the CO failure was corrected. Although the other responses are not incorrect, response B is most likely.

2. The readings shown above were recorded during an injector balance test. All of the following symptoms are consistent with the test results EXCEPT:
A. Lack of power
B. Rough idle
C. High CO emissions
D. Hard start
The correct answer is C The injector balance test clearly show that injectors No. 2 and No. 4 have poor flow. This is indicated by the low pressure drop readings of 9 psi and 6 psi. The specifications call for a minimum pressure drop of 21 psi, it’s obvious that the cylinders served by these injectors are being starved of fuel. With two misfiring cylinders, the engine would not only idle rough and lack power, but it would also be harder to start. The lack of fuel in the affected cylinders is causing a lean misfire. Since carbon monoxide is a product of a rich mixture, an increase in CO would not be a symptom consistent with the indicated test results.

3. The Immobilizer Module on the composite vehicle will do all of the following EXCEPT:
A. Disable injectors if the keycode is invalid
B. Verify the key code
C. Stop operation of the starter motor
D. Recognize the ECM ID number
The correct answer is CAnswer A is correct. The immobilizer module cannot stop operation of the starter motor.The immobilizer module requires the use of a coded key, and the module will verifY that the correct key is being used. The module will also recognize the ECM by ID number. If the keycode is determined to be invalid, the module will not allow operation of the injectors.

4. There is a P0420 “low catalyst efficiency” diagnostic trouble code stored in the memory on a vehicle with a MIL light illuminated. Technician A says that leaking exhaust system may have triggered the problem. Technician B says that the root cause of the problem may be worn valve guide seals. Who is correct?
A. Technician A only
B. Technician B only
C. Both Technicians
D. Neither Technicians
The correct answer is C Because there is a direct link between a converter’s ability to reduce emissions and its ability to store and release oxygen, the Catalyst Efficiency Monitor evaluates converter performance based on the signals from the upstream and downstream oxygen sensors. Under normal conditions, the signal from the upstream sensor will be switching above and below the transition point of .450V, while the output from the downstream sensor will remain relatively stable at about 1/2 a volt. However, as converter performance deteriorates the signal from the downstream sensor will begin switching. Once the number of downstream switches exceeds a calibrated threshold under specific operating conditions, the Catalyst Monitor will fail. A DTC P0420 can be triggered by mechanical problems such as a leaking exhaust system, worn valve seals or a blown head gasket. A leaking exhaust system affects the stability of the oxygen sensor signals, while oil or antifreeze in the combustion gases contaminates the oxygen sensors and converter alike. Over time, these conditions reduce the performance of the sensors and converter to the point of monitor failure.

5. According to the test results, which of the following conditions caused the vehicle with acontinuous return injection to fail the low-speed portion of a two-speed idle test?
A. Clogged PCV valve
B. EGR valve not seating
C. Restricted fuel return line
D. Faulty pressure regulator
The correct answer is B First of all the answer’s A, C, and D would cause the engine to run too rich. If this were the case, carbon monoxide would be well over the limit of 1.2%. The readings shown on the inspection report are indicative of an engine misfire. This can be seen in the hydrocarbon level of 855 ppm, which is nearly four times the legal limit. The low CO reading of 0.14% also supports this diagnosis, since carbon monoxide is a product of combustion. When an EGR valve hangs open at closed throttle, it creates excessive charge dilution. As a result, the mixture becomes too weak to burn and the engine misfires. Once the throttle is open, the engine runs normally. This is because the EGR valve is designed to open during that time anyway.

6. The ignition coils on the composite vehicle are being tested with an ohmmeter. Which of these are within specification for the secondary winding?
A. 7500 ohms
B. 11 M ohms
C. 1.5 ohms
D. 8.25 K ohms
The correct answer is D The correct resistance value for the secondary winding is 10k ± 2k ohms. Response A is obviously incorrect since 7500 ohms is too low. Response B is also wrong, only this time the specification is far too high. A reading of 11M represents 11 million ohms. The letter ‘M’ is used to denote the prefix ‘mega,’ which indicates one million. Response C is wrong because it shows the proper resistance for the primary winding, not the secondary. A reading of 8.25k ohms equals 8,250 ohms, which falls within the proper resistance range. The letter ‘k’ stands for the prefix ‘kilo,’ which means one thousand.

7. Cylinder number 4 is misfiring on the composite vehicle . All of the following could be the cause EXCEPT:
A. Open circuit at pin 11 of the ECM
B. Open circuit at pin 10 of the ECM
C. Open circuit at pin 41 of the ECM
D. Faulty ignition coil
The correct answer is B A faulty coil could cause the cylinder to misfire. Pin 41 pulses the injector for cylinder No. 4 and could also cause the misfire. Pin 11 triggers the coil for cylinder No. 4 and could also be the cause. However, pin 10 triggers coil No. 2, which would not cause a misfire in cylinder No. 4.

8. The composite vehicle has an illuminated MIL and has stored a DTC for EVAP system failure. Which of the following could be the cause?
A. The canister vent solenoid resistance is 49 ohms
B. The gas cap is too tight
C. A poor connection at ECM terminal 36
D. Blown fuse No. 4
The correct answer is C First of all the canister vent solenoid has a normal resistance range of 42-54 ohms. A reading of 49 ohms is within that specification, and therefore does not indicate a problem. A study of the wiring diagram shows that fuse No. 4 supplies all of the ECM controlled actuators. If this fuse were blown, an EVAP system failure would be the least of the problems. The vehicle would not even start! Obviously an over tightened gas cap may be difficult to remove but will have no effect on EVAP operation. Only if the gas cap were loose, would the EVAP monitor fail. This is because a loose gas cap would prevent the system from sealing during the EVAP system leak check. The canister vent solenoid requires proper power and ground signals in order to operate. Power comes from fuse No. 4, while the ECM provides the ground at terminal 36. Once energized, the canister vent solenoid blocks the fresh air supply to the canister in preparation for the leak test. If there is a poor connection at terminal 36, the vent solenoid will not operate and the leak test will fail.

9. The ISC motor toggles back and forth at closed throttle on an overhead valve V8 with DI ignition. A permanent magnet sensor inside distributor is used to generate RPM signal. Technician A says that the problem may be the result of a worn distributor shaft gear. Technician B says that a loose timing chain could be the cause of the problem. Who is correct?
A. Technician A only
B. Technician B only
C. Both Technicians
D. Neither Technicians
The correct answer is C An idle speed control motor regulates idle by physically changing the position of the throttle lever. This is accomplished using a plunger that extends from the motor housing. A throttle switch inside the ISC assembly, closes whenever the throttle lever contacts the plunger. This signals the ECM to take control of engine speed. In turn, the ECM activates the reversible motor as needed to provide the desired rpm. This value is programmed by the coolant temperature, accessory load, and other variables. Consequently, if the programmed idle speed is 600 rpm at normal operating temperature and no load, the ECM will extend or retract the plunger until actual engine speed equals a predetermined value. In order for the ECM to match closed throttle rpm to the programmed value, it must receive a reliable rpm input. This allows the ECM to determine if idle speed needs to be raised or lowered. However, if the rpm signal is erratic, the ECM will be theoretically incapable of matching the actual speed to the desired speed. Consequently, it will continue to hunt for idle by toggling the ISC plunger back and forth. The question indicated, the rpm signal is produced by a sensor inside the distributor. Since the distributor is driven by the camshaft in an overhead valve engine, a loose timing chain or worn distributor shaft gear could cause an erratic rpm signal. Therefore, both technician suggestions could be the root cause of the toggling ISC motor.

10. The composite vehicle will not shift past second gear. The resistance of both shift solenoids is 24 Ohms. Technician A says that the shift solenoids are defective. Technician B says there could be an open circuit to pin 74 of the TCM. Who is correct?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
The correct answer is D Neither technician is right. 24 Ohms is the correct resistance for the shift solenoids. In addition, if both shift solenoids were defective the vehicle would not engage any drive range. Shift solenoid 1 is used to engage drive range 1 and reverse so the shift solenoid is functional. Technician A is therefore incorrect. Technician B is also incorrect because the connection to pin 74 of the TCM engages shift solenoid 1, which is functional. Shift solenoid 2 is engaged through a circuit connected to pin 75 of the TCM.

11. All of the following will disable the A/C compressor clutch on the composite vehicle EXCEPT:
A. Open circuit at pin A of the A/C pressure sensor
B. Open circuit at pin 5 of the ECM
C. A short on the A/C request switch circuit
D. Open circuit at pin B of the A/C pressure sensor
The correct answer is C When the A/C request switch is closed it commands the ECM to engage the A/C compressor clutch. If the circuit is shorted, the A/C clutch would remain on, so a shorted switch would not cause the stated condition. An open circuit at pin 5 of the ECM would prevent engaging the dutch. Pin A of the A/C pressure switch is the 5-volt reference for the sensor. Loss of this connection would result in a low voltage input to the ECM, and the A/C clutch would be disabled. A loss of the ground connection at pin B would result in a high voltage input to the ECM, and the A/C clutch would be disabled.

12. The composite vehicle has an unstable idle, the MIL is on and a DTC P0300 “random cylinder misfire” is stored. According to the scan data shown which of the following could be the root cause of the problem?
A. Vacuum leak
B. Faulty ignition coil
C. Clogged injector
D. EGR valve not seating
The correct answer is A Although each of the responses describes a condition capable of triggering a misfire code, the only failure consistent with the scan data is an EGR valve that is not seating. The clues to this diagnosis can be found by looking at the H02S voltages and fuel trim readings. Notice that both upstream oxygen sensor readings are well above 600 millivolts, and fuel trim values are in the negative range. This is because there is less oxygen in an EGR diluted mixture. While these readings are also indicative of a rich condition, this is not one of the available choices. Besides, if the engine were running rich enough to trigger a misfire code, the upstream H02S voltages would tend to be higher than the displayed values, and the fuel trim readings would be closer to the control limit of -30%. As mentioned earlier, the conditions described in choices B, C, and D could also cause a misfire. However, the response from the closed loop system would be quite different. For example, if one of the ignition coils were bad, combustion would not occur in the affected cylinder, and a lean air/fuel mixture would cause low O2 sensor voltage and high fuel trim readings. This is because the oxygen normally used in combustion would simply pass through the cylinder unchanged. The ECM would take similar action if a clogged injector or vacuum leak were causing a lean misfire. Incidentally, notice that the MAP value of 2.3V is well above the normal closed throttle reading as is the 15% TAC value. The high MAP is due to the reduction in vacuum that occurs during a misfire, while the increase in TAC setting is an attempt by the ECM to achieve the desired idle speed.

13. The composite vehicle failed an I/M 240 test for excessive NOx. Which of the following conditions could be causing the problems?
A. A weak EGR diaphram spring
B. The EGR supply tube is clogged
C. A stuck open thermostat
D. A leaking fuel injector
The correct answer is B A weak diaphragm spring would result in greater EGR flow. Under this condition, the engine would most likely exhibit an off idle hesitation, since the EGR valve would open with less applied vacuum, therefore answer A is incorrect. Answer C is also incorrect. A stuck-open thermostat will cause the engine to run cold, which would cause an increase in hydrocarbon emissions, not oxides of nitrogen. The last answer D is incorrect also. A leaking injector will drive the air/fuel ratio rich. This will not only cause carbon monoxide emissions to rise, but will actually lower NOx emissions to the reduction in combustion temperature. Answer B is correct because any condition that raises combustion temperatures will cause an increase in NOx emissions. The temperature increase can come from outside the combustion chamber, as in the case of an inoperative cooling fan for example, or within the combustion chamber, as would be the case if the vehicle had a restricted EGR supply tube.

14. The composite vehicle has high mileage and a low power complaint. The MAP sensor reads 1.76 volts at idle and at a steady 2000 rpm. Technician A says a compression test should be done to check engine condition. Technician B says the engine should be checked for a vacuum leak. Who is correct?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
The correct answer is A At a steady 2000 rpm vacuum should be higher than it is at idle if the piston rings are sealing properly. In this case it is not, and technician A is correct in wanting to perform a compression test to check engine condition. The MAP sensor is giving a measurement of engine vacuum, one of the most effective measurements of most engine defects. A MAP voltage of 1. 76 volts indicates an engine vacuum of approximately 17 inches of Mercury, which is acceptable at idle speed. A vacuum leak would cause a lower reading than this, therefore Technician B is incorrect.

15. The CKP (crankshaft position sensor) waveform above was taken from composite vehicle while cranking. Which of the following best describe the waveform?
A. The CKP sensor is faulty
B. The CKP sensor is miss-adjusted
C. The pattern is normal
D. The reluctor has a chipped tooth
The correct answer is D The CKP sensor generates an AC voltage that varies in frequency and amplitude as engine speed changes. The 35-tooth reluctor causes the sensor to produce thirty-four 10-degree pulses and one 20-degree pulse each crankshaft revolution. As the pattern shows, sensor output is above the minimum acceptable level of 0.5 VAC, and the 20-degree sync pulse is clearly visible. This eliminates the possibility of a faulty sensor. It also dispels the notion that the sensor is mis-adjusted. The pattern shown here is abnormal. Notice that the amplitude of one 10-degree pulse is lower than the rest. This could only be the result of a chipped tooth on the reluctor. When that tooth aligns with the sensor, it creates a wider than normal gap and is unable to affect the magnetic field in the same way as the others. The lower pulse indicates this.

16. All of the following conditions must be met for the composite vehicle to enter closed loop EXCEPT:
A. Voltage inputs from the oxygen sensors
B. MAP sensor voltage between 1.5 and 2.0 volts
C. Ten seconds operating time since start-up
D. Coolant sensor voltage of 2.93 volts
The correct answer is B The MAP sensor on the composite vehicle is only used for OBD II diagnostic purposes and is not required to enter closed loop. To enter closed loop the composite vehicle must be warmed to at least 160°F, the oxygen sensors must be active, and the engine must be operating for at least ten seconds.

17. A vehicle fails an I/M 240 test for excessive NOx emissions. Technician A says that the engine may have excessive intake valve deposits. Technician B says that a restricted air filter may be causing the problem. Who is correct?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
The correct answer is A Technician A is correct, Intake Valve Deposits (IVD) not only upset mixture flow, but tend to absorb fuel as well. Therefore an engine with IVD runs leaner than normal. In addition to reduced performance, a lean mixture causes combustion temperatures to increase, resulting in greater NOx emissions. Oxides of nitrogen (NOx) form when nitrogen and oxygen come together under the heat and pressure of combustion. Consequently, every vehicle produces a certain level of NOx. However, when an engine operates above its normal maximum temperature, which is about 220oF (104°C), the corresponding increase in combustion temperature causes a proportional rise in NOx emissions. Since a restricted air filter would drive the air/fuel ratio rich, and because a rich mixture lowers combustion temperature, Technician B’s answer is incorrect.

18. The composite vehicle has no fuel pressure. Technician A says that the problem could be a poor connection at ECM terminal 5. Techni­cian B says that the problem could be the result of a blown No. 3 fuse. Who is correct?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
The correct answer is B Terminal 5 of the ECM is the ground control for the A/C clutch relay so you could immediately eliminate Technician B’s answer. The fuel pump on the composite vehicle is activated through an ECM controlled relay. A failure in the relay or control circuit will result in the condition described in the question, which is no fuel pressure. The fuel pump relay receives constant battery voltage at terminal ‘c’ through fuse No. 3. When the relay is energized by the ECM, the relay switch closes and power is applied to the fuel pump. When the ignition switch is in ‘START’ or ‘RUN,’ battery voltage is applied at terminal ‘a’ of the relay through fuse No. 4. The ECM supplies the ground at pin 4 to energize the relay coil. A poor connection at either point could result in no fuel pressure. If the relay switch circuit were open, which would be the case if fuse No. 3 were blown, the fuel pump would not operate, therefore Technician A is correct.

19. Refer to the wiring diagram to anwser this question: (click image for larger view) Technician A says that to check the voltage drop in the O2 ground circuit, the voltmeter leads should be connected between PCM terminals B15 and GND101. Technician B says that to check the voltage drop across the main relay switch contacts, the voltmeter leads should be connected between terminals B and D with the relay energized. Who is correct?
A. Technician A only
B. Technician B only
C. Both Technicians
D. Neither Technicians
The correct answer is B With the relay energized, battery voltage is applied to terminal B13 of the PCM, as well as the 02 heating element, injectors, generator, and ignition coils through splices 5100 and 5200. Under normal conditions, there should be virtually no voltage drop across the closed relay switch contacts. However, if there is excessive drop in this area, there will be less voltage available to power the previously mentioned devices. This could result in a variety of engine performance problems. To check the voltage drop, the leads would be placed as technician B indicated; between relay terminals B and D with the relay turned on. Excessive voltage drop in the 02 ground circuit (signal return) could create a false rich signal. To check voltage drop in this area, the voltmeter leads would be connected between terminal C12 at the PCM and G101 with the engine running. Connecting the leads as technician A indicated would result in a measurement of 02 sensor output voltage and is incorrect.

20. The composite vehicle fails a loaded mode I/M test for excessive hydrocarbons. which of the following is the root cause of the problem?
A. Shorted CMP signal wire to the ECM
B. Open CKP sensor
C. Poor connection at ECM terminal 12, the ground driver for ignition coil #6
D. Blown fuse#4, the ECM sensor volt reference
The correct answer is C Terminal 12 of the ECM is the ground driver for the number six ignition coil. A poor connection here would cause excessive voltage drop in the primary circuit. This would result in low secondary output to the number six spark plug, resulting in a partial misfire at best along with higher than normal hydrocarbons. If the CMP signal were shorted to ground, the engine would take longer to start. This is because the ECM would never see the 5V reference signal required to sequence the injectors and coils. However, once the engine was running, the missing CMP signal would have little effect on exhaust emissions. Therefore, response A is incorrect. Response B is also incorrect because an open CKP sensor would prevent the engine from starting at all. The engine would also fail to start if fuse No. 4 were blown (response D). Under this condition, all of the ECM controlled actuators, including the injectors and ignition coils, would lose battery power.

21. Once a zirconia oxygen sensor reaches operating temperature, how quickly should it respond to changes in the air/fuel ratio?
A. 50 microseconds
B. 100 milliseconds
C. One second
D. 1000 milliseconds
The correct answer is B In order for the ECM to maintain a proper air/fuel mixture, it needs to receive the 02 feedback signal quickly. This is why ‘response time’ is one of the performance standards used for oxygen sensors. The zirconia 02 sensor, which is the most widely used type, generates a signal between zero and one volt once it reaches operating temperature. As the oxygen content in the exhaust gas varies, sensor output voltage rises and falls. Rich mixtures have low oxygen and cause the sensor to generate voltages above 450 millivolts, while lean mixtures have high oxygen produce voltages below .450V. Just remember low voltage lean, high voltage rich. A properly functioning sensor will typically recognize a change in oxygen content within 100 milliseconds. A response time of 50 microseconds is too fast to be realistic and the times listed in responses C and D are not only the same, but are far too slow.

22. The waveform above was captured in closed loop at 1500rpm from the bank 1 oxygen sensor on the composite vehicle. What can be determined by an analysis of the waveform?
A. The engine is running lean
B. The sensor switching frequency is too slow
C. The sensor is functioning properly
D. The sensor response time is below normal
The correct answer is C The waveform in the picture displays normal operation of a good O2 sensor. A good zirconia oxygen sensor, which is the type found on the composite vehicle, will typically generate a voltage that switches between 200 and 800 millivolts at a frequency of at least 5 Hz (cycles per second). The time required to make the lean-to-rich and rich-to-lean transitions should be about 100 milliseconds.

23. A cylinder leakage test is being performed on a overhead valve V8 engine. When air is supplied to the number 4 cylinder a hissing noise is heard from the tailpipe. Technician A says the cam lobe for the #4 exhaust valve could be worn down. Technician B says that the #4 exhaust valve could be burned. Who is correct?
A. Technician A only
B. Technician B only
C. Both Technicians
D. Neither Technicians
The correct answer is B Burned valves prevent the affected cylinder from sealing properly. When the exhaust valve is at fault, combustion gases will be drawn into the cylinder during the intake stroke, and a portion of the air/fuel charge will be expelled into the exhaust system during the compression stroke. Likewise, when air is applied to a cylinder during a leakage test, it will escape out the tailpipe if the exhaust valve is not sealing. Technician As suggestion of a worn cam lobe is incorrect, since a worn lobe would prevent the exhaust valve from opening and would not have any affect on cylinder leakage.

24. All of the cylinders in an overhead cam engine have low compression. What is the MOST likely cause of this condition?
A. Burned valves
B. Broken timing belt
C. Worn piston rings
D. Leaking head gasket
The correct answer is B In most overhead cam engines, proper valve timing depends on the integrity of a toothed rubber belt. A broken belt allows the crankshaft to turn independently of the camshaft(s), which causes the valves and pistons to become out of phase. As a result, compression readings will be lower than normal on every cylinder. Although it is possible to have low compression on all cylinders due to burned valves, a leaking head gasket, or worn piston rings, they are less likely to be the root cause of the problem than a broken timing belt.

25. The usual number of terminating resistors on a CAN harness is:
A. One
B. Two
C. Three
D. Four
The correct answer is BLater vehicles are starting to use additional terminating resistors, but most CAN harnesses use two terminating resistors. The technician should verify this on a wiring diagram for a specific vehicle.

This post was written by: Martin Hand


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Martin Hand

About Martin Hand

ASE Certified L1 Advanced Mastertech. Martin Hand has over 15 years experience in Asian and European Import Auto Repair. Specializing in electrical diagnosis, engine performance, AT/MT transmission repair/rebuild. Martin is also pursuing a degree in Computers Science & Information Systems starting at Portland Community College while he plans to transfer to OIT. Certified in Java application level programming, experienced with other languages such as PHP, Ruby, JavaScript and Swift. Martin has future plans of automotive diagnostic software development.