ASE Practice Test #4 3

Question 1

A scan tool shows a DTC for the crankshaft position sensor (CKP) with no signal. The sensor has correct power and ground. What should the technician check next?

Accepted Answer

Inspect the reluctor (tone) ring on the crankshaft for missing, broken, or bent teeth, and check the sensor tip gap against specification

Answer

If the CKP sensor has correct power and ground but no signal, two possibilities remain: the sensor itself is faulty, or the reluctor ring is damaged (missing teeth, cracks, or excessive rust buildup that prevents signal generation). The air gap between the sensor tip and reluctor ring must also be within specification — too large a gap results in weak or no signal. Inspecting the reluctor ring visually and measuring the air gap are essential before condemning the sensor. A damaged reluctor ring requires crankshaft or harmonic balancer replacement.

Question 2

What does a scan tool "misfire counter" (OBD-II misfire monitor) count?

Accepted Answer

The number of crankshaft revolution intervals where insufficient power contribution is detected from a specific cylinder — tracked per-cylinder by detecting RPM fluctuations using the CKP sensor

Answer

OBD-II misfire detection uses the CKP sensor to precisely measure the time between each tooth of the reluctor ring. A cylinder that does not contribute power (from a misfire) causes the crankshaft to accelerate slightly less during that power stroke compared to firing cylinders. The ECM detects this subtle RPM variation and assigns it to the specific cylinder by tracking which cylinder was on its power stroke. The misfire counter tracks these events per cylinder per 200 and 1000 revolutions.

Question 3

A vehicle's steering pulls to the left only during light to medium braking, not during constant cruise. Which of the following is the MOST likely cause?

Accepted Answer

A restricted or collapsed right front brake hose — hydraulic pressure builds slower on the right, causing less right-side braking, allowing the left brakes to dominate and pull left

Answer

Brake pull occurs when braking force is unequal side-to-side. A collapsed internal brake hose acts as a one-way valve — hydraulic pressure can enter the caliper but cannot quickly exit when the pedal is released, causing the brake to stick (drag) or, if the restriction is severe, apply more slowly. If the RIGHT hose restricts pressure build-up, the right brake applies less force, causing the vehicle to pull LEFT toward the stronger braking side. After the vehicle stops and pressure is held, the hose may allow the caliper to eventually apply, but the initial pull has already occurred.

Question 4

What is the purpose of the knock sensor in a modern gasoline engine management system?

Accepted Answer

To detect engine detonation (knock) vibrations and signal the ECM to retard ignition timing to eliminate the knock, protecting the engine while maintaining maximum safe performance

Answer

The knock sensor is a piezoelectric device that detects the high-frequency vibration characteristic of engine detonation. When knock is sensed, the ECM immediately retards ignition timing by a few degrees. If knock stops, timing is gradually advanced back toward MBT (maximum brake torque) timing. This closed-loop knock control allows the engine to run at optimal (aggressive) timing under normal conditions while automatically protecting against knock caused by lower-octane fuel, hot temperatures, or high altitude — maximizing power and efficiency without engine damage.

Question 5

Which suspension geometry angle has the greatest effect on straight-line steering stability (returnability) after a turn?

Accepted Answer

Caster

Answer

Caster is the angle of the steering axis (the line through the upper and lower ball joints or the MacPherson strut axis) viewed from the side. Positive caster places the steering axis contact point ahead of the tire's contact patch, creating a self-centering trail effect — just like a shopping cart wheel. More positive caster provides better straight-line stability and stronger steering return-to-center after a turn. Insufficient caster results in a wandering, low-effort steering feel that requires constant correction.