Smog Repair Technician Exam Questions and Answers.

Smog Repair Technician Exam Questions
and Answers
Question 1
During a leakdown test, air is heard escaping through the throttle body. What is the
most likely cause?
Correct Answer
A burnt or stuck-open intake valve



Question 2
A car fails for excessive CO emissions at idle and has a P2196 (O2 Sensor Signal Stuck
Rich - Bank 1, Sensor 1) trouble code. What could be causing this failure?
Correct Answer
A faulty upstream oxygen sensor



Question 3
A technician wants to command the EVAP purge valve to open and close to verify its
functionality while diagnosing an emissions-related issue. Which mode should they
use?
Correct Answer
Mode 8



Question 4
If the O₂ reading after the cat is high, what does this suggest?
Correct Answer
The catalyst may not be using oxygen effectively




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,Question 5
A car is misfiring and has no DTC codes, what mode will assist the technician?
Correct Answer
Mode 6



Question 6
Which of the following is a common symptom of a stuck-closed EGR valve?
Correct Answer
High NOx emissions



Question 7
The engine does not crank at all when the key is turned. What could be the cause?
Correct Answer
Open fuse #31



Question 8
The engine will not start, and there is no crank. What is the likely cause?
Correct Answer
Open fuse #41



Question 9
A vehicle fails a smog test due to high hydrocarbon (HC) emissions. The STFT is
around -5%, and the LTFT is at -18%. What could be the cause?
Correct Answer
leaking fuel injector




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,Question 10
A vehicle with high HC and CO emissions fails smog. The STFT is -7%, and LTFT is
-15%. The PCV valve is suspected. What is a likely issue?
Correct Answer
stuck-closed PCV



Question 11
During a compression test, the following results were noted:
Cylinder 1: 150 psi
Cylinder 2: 150 psi
Cylinder 3: 80 psi
Cylinder 4: 150 psi
What is the most likely cause of the compression loss in Cylinder 3?
Correct Answer
Blown head gasket



Question 12
During a catalytic converter efficiency test, you observe that the temperature
difference between the inlet and outlet of the catalytic converter is less than expected.
What does this likely indicate?
Correct Answer
The catalytic converter is likely clogged or degraded



Question 13
A technician performs a leakdown test and records the following results:
Cylinder 1: 12% leakage
Cylinder 2: 10% leakage
Cylinder 3: 45% leakage
Cylinder 4: 11% leakage
Correct Answer
Remove the oil cap and listen for escaping air to check for piston ring issues




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, Question 14
For oxygen sensor testing what are they measured by?
Correct Answer
Millivolts



Question 15
A car came to do a smog and failed the smog due to incomplete monitors. What
resource should the technician use?
Correct Answer
On-Board Diagnostic Test Reference



Question 16
The engine starts, runs for a second, and then dies. No DTCs are present. Which fuse
could be to blame?
Correct Answer
Fuse #43



Question 17
A vehicle fails a Smog Check due to high CO (carbon monoxide) emissions and has a
P0172 (System Too Rich - Bank 1) trouble code. What is the best first step in
diagnosing the problem?
Correct Answer
Check the oxygen sensor readings and fuel trims



Question 18
Pins 4 & 5
Correct Answer
(Ground Issues) → If the scan tool fails to communicate, check these first. Poor
grounds can also cause erratic sensor data, leading to false smog failures.




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