ASE - Automotive Service Excellence Practice Test #5 1 — Questions and Answers
Question 1: A technician observes Long Term Fuel Trim (LTFT) values of +22% at idle that drop to approximately +5% at 2,500 RPM. Which condition BEST explains this pattern?
- A faulty mass airflow (MAF) sensor reading low across all RPM ranges
- A vacuum leak introducing unmetered air primarily at idle (Correct answer)
- Leaking fuel injectors causing an overly rich mixture
- A restricted catalytic converter increasing backpressure
Correct answer: A vacuum leak introducing unmetered air primarily at idle
Vacuum leaks allow unmetered air to enter the intake manifold. At idle the leak represents a large percentage of total airflow, so the PCM compensates heavily with positive fuel trim. At higher RPM, commanded airflow dwarfs the leak volume and fuel trim normalizes. A bad MAF would show elevated trim across all RPM ranges.
Question 2: A downstream (post-catalyst) oxygen sensor displays the same rapid, high-amplitude switching pattern as the upstream sensor. What does this waveform indicate?
- The upstream oxygen sensor has an open heater circuit
- The catalytic converter is storing and releasing oxygen efficiently
- The catalytic converter has low conversion efficiency (Correct answer)
- The downstream sensor signal wire is shorted to battery voltage
Correct answer: The catalytic converter has low conversion efficiency
A healthy catalyst stores excess oxygen and releases it as needed, causing the downstream O2 sensor to switch slowly and with low amplitude. When the downstream sensor mimics the upstream sensor's rapid switching, the catalyst is no longer buffering oxygen, indicating it has lost its conversion efficiency.
Question 3: A vehicle equipped with ABS consistently pulls to the right during a hard stop while ABS is actively cycling. Brake fluid level and pad thickness are within spec on all corners. Which component should the technician inspect FIRST?
- The brake master cylinder for an internal bypass
- The left-front wheel speed sensor and tone ring
- The right-front wheel speed sensor and tone ring (Correct answer)
- The hydraulic control unit (HCU) modulator valve
Correct answer: The right-front wheel speed sensor and tone ring
ABS individually modulates brake pressure at each wheel based on wheel speed sensor data. If the right-front sensor is providing an incorrect signal, the ABS module may prematurely release or apply pressure on that corner, creating a pull toward the side with the faulty sensor input.
Question 4: An automatic transmission slips specifically during the 2nd-to-3rd gear upshift under heavy throttle. Fluid level, color, and smell are all normal. No other gear changes are affected. Which component is MOST likely at fault?
- The torque converter clutch (TCC) solenoid
- The 2-3 shift solenoid or its wiring circuit (Correct answer)
- The transmission range (TR) sensor
- The turbine (input) speed sensor
Correct answer: The 2-3 shift solenoid or its wiring circuit
Each shift solenoid in an automatic transmission controls a specific gear change. A faulty 2-3 shift solenoid or an open/short in its circuit causes the clutch pack or band for 3rd gear to engage incompletely, resulting in slippage only during that transition. Other gear changes use different solenoids and are unaffected.
Question 5: A smoke test reveals no leaks in the EVAP system. The purge solenoid opens on command and the vent solenoid closes on command, yet the EVAP monitor continues to report incomplete. Which component is MOST likely preventing monitor completion?
- A faulty fuel tank pressure (FTP) sensor (Correct answer)
- A cracked charcoal canister body
- A stuck-open purge valve
- A loose or missing fuel cap
Correct answer: A faulty fuel tank pressure (FTP) sensor
The EVAP monitor seals the system (closes the vent, opens purge) and then uses the fuel tank pressure sensor to confirm vacuum or pressure builds within the system. If the FTP sensor is faulty or out of calibration, the PCM never receives confirmation that the system sealed, so the monitor aborts even though the hardware is functioning correctly.
Question 6: A dial indicator measurement shows 0.009 inch of lateral runout on a front brake rotor. The manufacturer's maximum specification is 0.003 inch. Which customer symptom is MOST consistent with this finding?
- Brake fade and boiling fluid after repeated hard stops on a steep grade
- A pulsating brake pedal and steering wheel shimmy during normal braking (Correct answer)
- A continuous metal grinding noise present only at speeds below 10 mph
- ABS activation on dry pavement at light braking pressure
Correct answer: A pulsating brake pedal and steering wheel shimmy during normal braking
Excessive lateral runout causes the rotor to wobble side to side as it rotates. Each revolution pushes the brake pads outward and then allows them to relax, creating a pressure pulse in the hydraulic circuit that the driver feels as pedal pulsation. The resulting force variation can also transmit through the steering linkage as a shimmy.
ASE - Automotive Service Excellence Practice Test #5 1
A technician observes Long Term Fuel Trim (LTFT) values of +22% at idle that drop to approximately +5% at 2,500 RPM.
Which condition BEST explains this pattern?