Smog Repair Technician Practice Exam

These questions are part of the practice quiz. Start practicing

• What symptom may indicate a malfunctioning EGR system?
• What could be the effect of a faulty MAF sensor based on oxygen sensor readings?
• Which substance is commonly emitted by vehicles and contributes to smog formation?
• During a smog check, if a vehicle shows codes related to the EVAP system, what is a recommended first action?
• What could pressure leaking from the oil filler cap during a leakdown test indicate?
• What should a technician check next when a scan tool shows no power at the vehicle's OBD-II port but grounding is good?
• What is the effect on carbon monoxide levels when proper air temperature is maintained during cranking?
• Which mode will help in checking permanent trouble codes in a vehicle?
• A vehicle fails a smog check with high NOx emissions. The technician removes the EGR valve and finds no carbon buildup. What should be checked NEXT?
• Which of the following is a common symptom of a stuck-closed EGR valve?
• Under what condition can a Test-Only smog station sublet an inspection?
• What is the purpose of Mode 4 in onboard diagnostics?
• If a car fails a smog check due to high NOx emissions and has an LTFT of +25%, what is the most likely cause?
• If a customer reports that their check engine light turned on briefly but is now off, which mode should a technician use to check for unconfirmed trouble codes?
• What is the expected resistance for a secondary ignition coil?
• A downstream O2 sensor fluctuating like the upstream sensor usually indicates what?
• A technician records a leakage test with Cylinder 3 at 45%. What should be the next step?
• Failure of which component may result in a high level of hydrocarbon emissions?
• What is a common cause of a failed emissions test indicated by a P0455 code?
• What identifying factor can suggest issues with a vehicle's fuel injectors?
• What are typical signs that a leaking fuel injector is present in a vehicle?
• What is the most likely cause of smog test failure in a car with HC at 90 ppm, CO at 0.1%, and NOx at 2400 ppm?
• What data is indicated by Mode 1 in diagnostic testing?
• What mode focuses on the control of onboard systems?
• Which mode is used for displaying Freeze Frame Data during a diagnostic test?
• What is a likely cause if the post-catalytic converter O2 sensor shows irregular readings?
• A good catalytic converter will typically show a(n) _____ in CO₂ after the converter.
• To access vehicle information related to emissions compliance, which mode should a technician employ?
• What kind of repair is commonly required when a vehicle fails an emissions test?
• During a smog check, if the ignition timing check does not have manufacturer's engine speed tolerance, what is the acceptable idle speed range?
• Which sensor monitors the air/fuel ratio before the catalytic converter?
• In a compression test, results indicate Cylinder 4 is at 130 psi while Cylinder 3 is 70 psi. What might be the likely issue?
• During a leak-down test, air escaping through the intake manifold typically indicates what issue?
• Which of the following conditions can lead to high hydrocarbon emissions?
• During an emissions test, high hydrocarbon levels with normal oxygen sensor readings may indicate what issue?
• Which of the following is a common symptom of a faulty catalytic converter?
• What mode should a technician use to check real-time sensor data, including fuel trims and oxygen sensor readings, when diagnosing high NOx emissions?
• If a vehicle fails a smog check with high CO emissions and a P0172 trouble code, what is the best first step in diagnosing the issue?
• In a vehicle with low fuel pressure, what might be a potential diagnostic step?
• Which smog component is most responsible for reducing NOx emissions in a modern vehicle?
• Which issue could cause a car to run lean and fail a smog check due to high NOx emissions?
• How are oxygen sensors typically tested?
• Is an Oil Separator legal?
• If a car is running rich and shows STFT at -12% and LTFT at -15%, what is the potential issue?
• What is a likely sign of a failing catalytic converter in a vehicle?
• What test result would likely suggest piston ring damage?
• What results are provided by Mode 5 in the diagnostics?
• In what case would a technician conclude that a catalytic converter needs to be replaced?
• When diagnosing high NOx emissions, which system should be considered first for issues?
• To pass inspection, the base ignition timing must be within:
• A car is misfiring and has no DTC codes. What mode will assist the technician?
• What is the most likely reason for white smoke coming from an engine tailpipe?
• A vehicle with a lean condition at idle but normal fuel trim at higher RPMs likely has:
• What could a constant low voltage reading of around 0.2 volts from the front oxygen sensor during a catalytic converter test indicate?
• For a vehicle with a P0420 trouble code failing due to excessive NOx, what should be checked prior to replacing the catalytic converter?
• A car's air conditioning system blows warm air despite the compressor being activated. What could be causing this issue?
• Which of the following can result in better control of vehicle emissions?
• What is the most common cause of black smoke emitted from an engine?
• What should be confirmed if fuel trim readings are abnormal during diagnosis?
• When a compression test yields Cylinder 3 showing 80 psi while others are at 150 psi, what is the likely cause of compression loss?
• Which of the following gases tends to decrease when proper combustion occurs?
• When diagnosing high emissions issues, which mode allows a technician to view the results of O2 sensor tests?
• Which mode allows the technician to access onboard monitoring test results for non-continuous monitors?
• A lean fuel mixture can lead to what smog test result?
• How does the TAC system influence carbon dioxide emissions during cranking?
• A clogged PCV valve can cause which of the following smog-related issues?
• If no trouble codes are present and diagnostic tests need to be reviewed for emissions control devices, which mode is essential?
• In a smog test, if a vehicle's CO reading is 5.8% and HC is 280 ppm, what is the most likely cause of the failure?
• What can cause excessive tailpipe emissions?
• What does air escaping from the intake manifold during a leakdown test suggest?
• If the front oxygen sensor shows a low voltage of around 0.2 volts and the rear sensor shows a high voltage of 0.8 volts, what could this indicate?
• A car fails smog due to incomplete monitors and a "no communication" DTC. What should a technician do FIRST when diagnosing the issue?
• What does a temperature difference between the inlet and outlet of a catalytic converter indicate if it is less than expected?
• What impact does a faulty mass airflow sensor have on emissions?
• A P0171 (System Too Lean - Bank 1) code is set on an OBD-II vehicle. What should be checked FIRST?
• In a vehicle with high HC and CO emissions, what does a LTFT of -15% typically indicate when the PCV valve is suspected?
• If a vehicle failed smog due to high NOx and the catalytic converter is intact, what should be checked next?
• In a compression test where Cylinder 1: 90 psi, Cylinder 2: 100 psi, Cylinder 3: 80 psi, and Cylinder 4: 70 psi, what might be the cause of the low compression?
• What symptom might indicate a faulty oxygen sensor?
• A vehicle has a check engine light on. Which mode should the technician use to retrieve stored diagnostic trouble codes?
• If a vehicle shows an LTFT of -15% and fails a smog test, what might be the underlying issue?
• What is the implication of a vehicle having low levels of O₂ during a smog test?
• Which device helps to control emissions from gasoline-powered vehicles?
• If an oxygen sensor voltage range is 0.6 - 1.0V, what does it signify?
• What result indicates the catalytic converter is not reducing NOx properly?
• Which mode is appropriate for checking freeze frame data to see engine conditions when a diagnostic trouble code was set?
• Which issue is indicated by worn spark plugs if a vehicle's smog test results in HC of 160 ppm?
• Which of the following may indicate an issue with a vehicle's emissions system?
• What is typically indicated by a NOx reading of 2400 ppm in a smog test?
• What is the normal injector resistance?
• When a vehicle registers 70 psi in Cylinder 3, what is the most probable reason for this low reading?
• If an engine shows 160 psi in three cylinders and 0 psi in one, what is the likely cause of the 0 psi in that cylinder?
• Which emissions result can signify a defective catalytic converter upon smog testing?
• If a vehicle exhibits high NOx emissions along with LTFT at +18% and STFT fluctuating between +5% and +10%, what might be the issue?
• What is a typical indicator of a failing mass airflow sensor?
• What happens to oxygen levels during cranking when the TAC system operates correctly?
• If the compression in a cylinder improves after adding oil, what is the likely issue?
• What leak-down percentage is generally accepted as allowable in most engines?
• What can improper spark plug operation lead to in terms of emissions?
• What effect does a malfunctioning thermostat have on emissions?
• What is a key advantage of a leakdown test compared to a compression test?
• A vehicle with a P0430 code should have which of the following checked before replacing the catalytic converter?
• What does a vehicle's Engine Control Module (ECM) regulate to minimize emissions?
• Which component failure could cause a vehicle to exhibit a LTFT of -20% and STFT of -10%?
• A vehicle fails a compression test with readings of 80, 75, 70, and 65 psi across cylinders. What is the most likely cause of this compression loss?
• What is the most likely cause of high HC and CO emissions indicated by a P0455 trouble code?
• If a vehicle fails a Smog Check due to high HC and CO emissions and has a P0175 trouble code, what is the most likely cause?
• If a leakdown test reveals no escaping air from the intake manifold, what does this suggest?
• A vehicle fails smog due to excessive CO emissions. Which of the following is the MOST likely cause?
• What is a common symptom of a vehicle running too rich?
• A vehicle's engine stalls frequently at idle but runs fine at higher RPMs. What could this indicate?
• What is indicated when a vehicle’s exhaust gas analyzer shows high levels of hydrocarbons?
• What is the role of the oxygen sensor in emissions control?
• What is the purpose of an oxygen sensor in an exhaust system?
• During an inspection, you find that the EGR passages are clogged with carbon buildup. What effect will this have on emissions?
• A vehicle with CO₂ readings at 15.0% is likely suffering from what issue?
• What is a likely cause for excessive CO emissions at idle if the vehicle has a P2196 trouble code?
• What is the typical resistance measurement of a primary ignition coil?
• If a vehicle shows symptoms of excessive fuel consumption and poor performance, what is the first area a technician should check?
• If a customer has a failed VIR check report, what should the technician recommend?
• What is indicated by a significant increase in voltage from an oxygen sensor during operation?
• Which fuse should be inspected if there is excessive backfiring?
• If Cylinder 3 shows significantly lower compression compared to surrounding cylinders, what diagnostic measure should be prioritized?
• When a vehicle improperly adjusts air-fuel mixture resulting in rich running conditions, what component is often at fault?
• Which of the following components is primarily responsible for reducing NOx emissions?
• Why is it important to diagnose issues reported in a VIR check?
• During a leakdown test, if the pressure gauge shows significant loss of pressure while the exhaust valve is held open, what does this indicate?
• What is the most likely cause of the low compression in Cylinder 3 if it shows 0 psi during a compression test?
• What is the most probable cause for smog failure in a vehicle with HC at 180 ppm and CO at 3.8%?
• For a vehicle failing emissions testing without DTCs, what is the most appropriate mode to diagnose the catalyst and EGR system?
• After replacing a faulty ignition coil, the vehicle still has starting issues. What should be the next step?
• If a vehicle fails a smog check due to a communication error with the scan tool, which OBD-II pin should be checked first for proper power?
• What component measurement is critical for testing ignition systems?
• For catalyst testing, what results should you see with gases that can indicate a bad catalytic converter?
• Which statement is true about subletting smog inspections in California?
• Which mode would a technician use to command the EVAP purge valve to open and close during diagnosis?
• If all cylinders show around 110 psi during a compression test, what does this likely indicate?
• When performing a smog inspection, what is the key aspect to remember about documentation?
• What could be the suspected issue if a vehicle has a smog test result of HC: 210 ppm and NOx: 150 ppm?
• Which system primarily helps to reduce NOx emissions in a vehicle?
• What is the most likely cause of a cylinder showing 0 psi in a compression test?
• A car fails a smog test due to high HC (hydrocarbon) emissions. Which of the following could be the cause?
• A vehicle with a P0174 code is experiencing rough idle and hesitation under acceleration. What is the most likely cause?
• High NOx emissions in a vehicle's smog test could indicate what type of issue?
• What function does Mode 4 serve in automotive diagnostics?
• Which of the following could lead to high carbon monoxide (CO) emissions in a vehicle?
• When performing an ignition timing check at idle speed of 800 RPM, by how many RPM should the technician increase the engine speed?
• Which mode is referred to for pending Diagnostic Trouble Codes?
• What is a probable cause for low compression in multiple cylinders when values are closely similar but below normal levels?
• What does an oxygen sensor voltage reading of 0.4 - 0.5V suggest?
• Which pair of emission readings would most likely indicate a good catalytic converter?
• The vehicle starts but runs poorly, with reduced power and check engine light on. Which fuse could be the issue?
• What is a potential cause of poor fuel economy indicated by STFT of -8% and LTFT of -17%?
• Can a Test-and-Repair smog station in California sublet a smog inspection?
• After replacing the alternator, the vehicle's battery continues to show a low voltage reading. What might be the underlying issue?
• The engine will not start, and there is no crank. What is the likely cause?
• What is the most likely cause of a check engine light showing a "low fuel pressure" code?
• How does the TAC system affect hydrocarbon levels during engine cranking?
• What does Mode 3 represent in the diagnostic modes?
• What could cause a vehicle to fail for high NOx emissions with a P0128 trouble code?
• When diagnosing a vehicle with a P0420 trouble code, what should be done first?
• If a mechanic notices consistently negative fuel trim values across both banks, what could this suggest?
• What does a stable long-term fuel trim (LTFT) of -22% suggest about the engine?
• A vehicle displaying a P0171 trouble code and failing for high HC emissions likely indicates what issue?
• What is a typical sign of a good catalytic converter on a five-gas analyzer?
• What emissions result indicates a leaking fuel injector?
• What could cause high hydrocarbon (HC) emissions if STFT is around -5% and LTFT is at -18%?
• When checking for diagnostic trouble codes after an emissions-related repair, what is a vital first step?
• What could indicate a rich mixture in a vehicle leading to poor catalyst function?
• If a vehicle's STFT is stable at -10% and LTFT is at -22%, what might be responsible for excessive fuel consumption?
• What is the most likely cause of a cylinder starting at 30 psi and building up to 120 psi over multiple cranks during a compression test?
• What does an oxygen sensor voltage reading of 0.0 - 0.3V indicate?
• What is the most common cause of a Check Engine Light coming on related to emissions?
• What role does the vacuum leak play in engine performance issues?
• If the O₂ reading after the catalytic converter is high, what does this suggest?
• What is one of the first components to inspect when a vehicle displays a high LTFT reading?
• In the context of vehicle diagnostics, what does a fluctuating upstream O2 sensor signal indicate?
• In a leakdown test, what would a higher percentage of leakage generally indicate?
• The engine does not crank at all when the key is turned. What could be the cause?
• What problem can cause detectable air escaping during a leak-down test?
• Which mode should a technician use to view test results for all onboard diagnostic systems?
• What is the most likely cause of a vehicle failing a smog test with HC at 250 ppm, CO at 0.3%, and NOx at 2200 ppm?
• What is the most likely cause for the low compression of 30 psi in Cylinder 3 compared to higher readings in the other cylinders?
• What might indicate a failure of the voltage regulator in a vehicle?
• What is considered a normal range for fuel trims?
• What condition can contribute to a P0420 code indicating catalyst system efficiency below threshold?
• What is the primary purpose of a cylinder leakdown test?
• What is indicated by a compression test on a 6-cylinder engine showing Cylinder 3 at 100 psi while others are higher?
• If an engine has higher than normal HC readings, what is a potential cause other than fuel system faults?
• The engine starts, runs for a second, and then dies. No DTCs are present. Which fuse could be to blame?
• Which of the following would likely cause a vehicle to fail a smog test with excessively low CO levels?
• What fuel trim readings would confirm a catalytic converter issue rather than a fuel system problem?
• A post-catalytic converter oxygen sensor should ideally:
• What mode should be accessed to check if the ECM has saved a permanent record of a failure after clearing a trouble code?
• What is the most likely cause of having a normal oxygen sensor reading at idle but a rich reading during acceleration?
• What tool is typically used to measure backpressure in the exhaust system during a catalytic converter test?
• Which pin on the OBD-II connector is used for chassis ground?
• The check engine light is on, and the vehicle won't accelerate. Which component is likely the cause?
• During cranking, what happens to CO levels with improper air temperature?
• What does a Slipped Harmonic Balancer affect?
• Which mode will assist a technician if a car is misfiring and has no Diagnostic Trouble Codes (DTC)?
• The vehicle cranks normally, but it struggles to stay running. What fuse should be checked?
• In a vehicle that fails a smog test with HC at 220 ppm and CO at 3.2%, what is the most likely cause of the failure?
• What should a technician check if the vehicle has a weak spark?
• What is the function of a catalytic converter in terms of emissions?
• During a leakdown test, what is indicated if air is heard escaping through the throttle body?
• Which diagnostic trouble code is associated with a "System Too Lean" condition?
• What is the normal voltage range for a properly working upstream oxygen sensor?
• What does a steady voltage reading of 0.8 volts from the front (upstream) oxygen sensor likely indicate?
• A malfunctioning compressor in an AC system typically results in:
• What is the impact of the TAC system on nitrogen oxides during engine cranking?
• When STFT fluctuates between -2% and +2%, with LTFT at -5%, what does this indicate about engine performance?
• What is the acceptable procedure for ensuring that a vehicle’s fuel tank is tested correctly during an EVAP test?
• What mode should a technician use to retrieve the Vehicle Identification Number (VIN) and calibration ID from a vehicle's ECM?
• Which mode should be used to command the EVAP system running tests?
• What resource should a technician use when a car fails a smog due to incomplete monitors?
• What might reduced CO₂ levels indicate about a vehicle’s combustion process?
• Which mode should a technician use to erase stored Diagnostic Trouble Codes after repairing a vehicle's misfire issue?
• On a standard OBD-II connector, what is the function of Pin 6?
• What is a common cause of smog test failure indicated by HC at 300 ppm and CO at 4.5%?
• A technician wants to check the results of onboard diagnostic tests for components after a vehicle has failed an emissions test without any trouble codes. Which mode is appropriate?
• A vehicle's OBD-II connector shows no scan tool communication. Upon inspection, you find no voltage at Pin 16. What is the most likely cause?
• Which diagnostic trouble code (DTC) indicates a problem with the fuel mixture that is too rich on Bank 2?
• If Cylinder 1 has 150 psi and Cylinder 3 has 50 psi, what is the most likely cause of the low compression in Cylinder 3?
• A vehicle shows high HC and CO levels before and after the catalytic converter. What does this likely indicate?
• In a vehicle using CAN communication, which pins should be checked for proper signal operation if an OBD communication error is present?
• When diagnosing a vehicle with an STFT of +18% and an LTFT of +30%, what should be checked first?
• What condition could negatively impact the performance of an oxygen sensor?
• When testing catalytic converter efficiency, what reading indicates a failure of the catalytic converter?
• What function does the TAC system primarily serve regarding emissions?
• Which method is appropriate for confirming emissions failures indicated by stored unconfirmed trouble codes?
• What mode should be used to diagnose oxygen sensor issues by checking their test results on an older vehicle?