CAL Automotive Door and Trunk Lock Systems 2 — Questions and Answers
Question 1: What is the primary structural difference between a trunk lock cylinder and a door lock cylinder in most vehicles?
- Trunk locks use double-sided keys while door locks use single-sided keys
- Trunk lock cylinders typically have fewer wafer or tumbler positions (Correct answer)
- Trunk locks do not use a cam mechanism to engage the latch
- Trunk locks are always fully electronic with no mechanical override
Correct answer: Trunk lock cylinders typically have fewer wafer or tumbler positions
Trunk lock cylinders typically have fewer wafer positions (often 4–5) than door lock cylinders (often 6–8), reflecting a lower security priority for trunk access in most vehicle designs.
Question 2: A customer reports that power door locks work from the interior switch but not from the key fob. What is the most likely cause?
- Faulty BCM requiring reprogramming
- Broken interior door lock actuator
- Dead or weak key fob battery (Correct answer)
- Corroded door lock cylinder
Correct answer: Dead or weak key fob battery
Since the interior switch bypasses the RF signal path entirely and still works, a dead or weak key fob battery is the most common cause of remote-only failure.
Question 3: Which of the following best describes a 'passive entry' system on modern vehicles?
- The vehicle unlocks automatically when the authorized fob is in proximity without pressing any button (Correct answer)
- The vehicle uses a mechanical key only for exterior entry
- The door unlocks only after the ignition is turned to the on position
- Entry requires entering a PIN code on a door-mounted keypad
Correct answer: The vehicle unlocks automatically when the authorized fob is in proximity without pressing any button
Passive entry systems use low-frequency signals to detect an authorized fob within range and automatically unlock the door when the handle is touched, requiring no button press from the driver.
Question 4: When servicing a trunk latch that will not release via the interior handle, what component should be checked first?
- The BCM programming and key fob pairing
- The trunk weather stripping for compression issues
- The release cable or actuator rod for binding or disconnection (Correct answer)
- The transponder chip in the ignition key
Correct answer: The release cable or actuator rod for binding or disconnection
A binding, kinked, or disconnected release cable or actuator rod is the most common mechanical cause of trunk latch failure and should be inspected before checking electronic components.
Question 5: What does the term 'slam latch' refer to in automotive trunk systems?
- A latch requiring manual key operation every time the trunk is closed
- An electronic latch that opens only via a dashboard button
- A latch that engages automatically when the trunk lid is pressed closed (Correct answer)
- A safety latch that locks the trunk above a certain vehicle speed
Correct answer: A latch that engages automatically when the trunk lid is pressed closed
A slam latch (auto-latch) uses spring tension to engage automatically when the trunk lid is closed, eliminating the need to manually turn a key to secure it.
Question 6: If a door lock actuator tests good but the door still will not lock electrically, what is the correct next diagnostic step?
- Replace the entire door panel assembly
- Check the wiring harness and connectors in the actuator circuit for faults (Correct answer)
- Rekey the door lock cylinder
- Reprogram the key fob to the BCM
Correct answer: Check the wiring harness and connectors in the actuator circuit for faults
If the actuator itself is confirmed functional, the fault lies in the electrical circuit — inspecting the wiring harness and connectors for breaks, corrosion, or loose terminals is the logical next step.
Question 7: What is the primary reason automotive locksmiths must verify proof of ownership before performing a lockout or key replacement service?
- Federal FMVSS 206 mandates identity checks for all automotive services
- EPA emissions regulations require vehicle owner identification
- OSHA workplace safety standards require customer ID verification
- State locksmith licensing laws and professional ethics codes require ownership verification to prevent assisting in vehicle theft (Correct answer)
Correct answer: State locksmith licensing laws and professional ethics codes require ownership verification to prevent assisting in vehicle theft
State licensing regulations and industry codes of ethics require verifying ownership (registration, ID, or insurance) before any entry or key service to ensure the locksmith does not facilitate unauthorized vehicle access.
CAL Automotive Door and Trunk Lock Systems 2
What is the primary structural difference between a trunk lock cylinder and a door lock cylinder in most vehicles?