Electrical and Electronic Systems A6 Flashcards

A technician measures 14.1 volts at the battery with the engine running at 2,000 RPM. The headlights and other accessories are on. Is this reading normal?

Answer: Yes, 13.5-14.5 volts is the normal charging voltage range

A charging system voltage of 13.5-14.5 volts (some manufacturers specify up to 14.8V) with accessories on and the engine running is normal. This voltage is sufficient to charge the battery and power all vehicle systems without overcharging.

A technician performs a voltage drop test across a ground connection and measures 0.4 volts. The specification is less than 0.1 volt. What does this indicate?

Answer: The connection has excessive resistance causing voltage drop and reduced circuit performance

A voltage drop of 0.4 volts across a ground connection exceeds the maximum 0.1-volt specification, indicating excessive resistance at that connection. This resistance reduces effective circuit voltage, causes components to underperform, and can cause overheating at the connection point.

A technician is using an oscilloscope to test a crankshaft position sensor (CKP). The waveform shows the expected pattern but is missing one group of pulses at regular intervals. What does the missing pulse group indicate?

Answer: A reference window or timing notch in the reluctor ring that the CKP uses as a TDC reference signal

Most CKP sensor reluctor rings have a gap (missing tooth or teeth) that creates a missing pulse or pulse gap in the sensor output. The ECM uses this 'missing tooth' reference to identify a specific crank position, typically used as a cylinder identification or TDC reference point.

A customer's battery repeatedly goes dead overnight. The charging system tests normal. A current drain test shows 150 milliamps with all doors closed and the vehicle in sleep mode. The specification is less than 50 milliamps. What is the procedure to find the source of the parasitic drain?

Answer: Remove fuses one at a time while monitoring current until the drain drops to within specification

To locate the circuit causing parasitic drain, remove fuses one at a time while monitoring total drain current with an ammeter in series with the battery. When removing a fuse causes the current to drop to within specification, the circuit protected by that fuse contains the source of the drain.

What does the term 'duty cycle' mean when describing the operation of a fuel injector or other solenoid controlled by the PCM?

Answer: The percentage of time the component is ON (energized) during each operating cycle

Duty cycle is the percentage of an operating cycle during which a component is energized (ON). A 50% duty cycle means the component is on for half and off for half of each cycle. Pulse-width modulation (PWM) varies duty cycle to control component output, such as fuel injector pulse width for fuel metering.

A technician is diagnosing an intermittent no-start condition. The starter cranks the engine but it will not fire. A check with a test light shows the injectors are not being commanded during cranking. The PCM has a power and ground. What should be checked NEXT?

Answer: The crankshaft position sensor signal during cranking

The PCM will not command injector operation without receiving a valid crankshaft position signal. If the PCM has power and ground but the injectors are not activated during cranking, the most likely cause is a missing or invalid CKP sensor signal — the PCM cannot determine crank position to time injection.