Electrical and Electronic Systems Flashcards

What is the purpose of the knock sensor in an engine management system?

Answer: To detect detonation and signal the ECM to retard ignition timing

The knock sensor is a piezoelectric sensor that detects the vibration frequency of detonation (knock). When knock is detected, the ECM retards ignition timing to prevent engine damage.

A scan tool shows a P0300 diagnostic trouble code. What does this indicate?

Answer: Random or multiple cylinder misfire detected

P0300 indicates random or multiple cylinder misfires. Unlike P0301–P0312, which identify a specific cylinder, P0300 means the misfire pattern does not consistently point to a single cylinder.

What is the function of a relay in an automotive electrical circuit?

Answer: To allow a low-current switch circuit to control a high-current load circuit

A relay uses a small current through its coil to create a magnetic field that closes a switch for a higher current circuit, protecting the control switch and wiring from high current loads.

When diagnosing a no-start condition, the starter motor clicks but the engine does not crank. What is the most likely cause?

Answer: A discharged battery or poor battery cable connections

A clicking starter with no cranking indicates insufficient current reaching the starter. This is most commonly caused by a discharged battery, corroded terminals, or loose battery cable connections.

What does the duty cycle of a pulse-width modulated (PWM) signal represent?

Answer: The percentage of time the signal is in the ON state during one complete cycle

Duty cycle is expressed as a percentage representing the ON time versus the total cycle time. For example, a 60% duty cycle means the signal is ON for 60% and OFF for 40% of each cycle.

What type of tool is required to reprogram or flash an engine control module?

Answer: A factory-level scan tool or J2534 pass-through device with manufacturer software

Module reprogramming requires a factory scan tool or a SAE J2534-compliant pass-through device connected to a PC running the manufacturer's calibration software, plus a stable power supply to prevent corruption.