Electrical and Electronic Systems Flashcards

What is the function of the throttle position sensor (TPS)?

Answer: To signal the ECM the angle and rate of change of the throttle plate opening

The TPS provides the ECM with a voltage signal proportional to throttle plate angle and how quickly it changes, which the ECM uses for fuel delivery, timing, and transmission shift calculations.

A multiplexed vehicle has total communication failure. Neither the scan tool nor any module responds. What should the technician check first?

Answer: The CAN bus terminating resistors and bus wiring for opens or shorts

Total CAN bus failure preventing all communication suggests a bus-level problem: shorted or open CAN-H/CAN-L wires, or failed terminating resistors (normally 60 ohms each, 120 ohms total measured between CAN-H and CAN-L).

What is the purpose of the starter motor overrunning clutch (Bendix drive)?

Answer: To disengage the starter drive from the flywheel after the engine starts

The overrunning clutch allows the starter pinion to engage and drive the flywheel during cranking, but freewheels when the engine starts and spins faster than the starter, preventing starter motor damage.

A scan tool shows long-term fuel trim (LTFT) at +25%. What does this indicate?

Answer: The ECM is adding 25% more fuel than the base fuel map to maintain stoichiometric ratio

A positive LTFT of +25% means the ECM has learned to add 25% more fuel than the base map because the engine was running lean. This could indicate a vacuum leak, low fuel pressure, or weak injectors.

What is the purpose of the immobilizer system in a modern vehicle?

Answer: To disable the fuel and/or ignition system unless the correct transponder key is detected

The immobilizer system communicates with a transponder chip in the key. If the correct code is not received, the system disables fuel injection and/or ignition, preventing the engine from starting even if the key turns.

When measuring resistance of a component, why must the circuit be de-energized?

Answer: To prevent the external voltage from causing inaccurate readings and potentially damaging the ohmmeter

An ohmmeter applies its own small voltage to measure resistance. External circuit voltage will add to this, producing false readings, and can damage the sensitive measuring circuit inside the meter.