Ohm's Law and Circuits
This is the definition of a parallel circuit.
What is a circuit that has more than one path to ground
This is the function of a relay.
What is using a small current switch to control a large current switch
This condition might cause circuits and components to not operate normally or operate slowly.
What is high resistance?
What is the most likely cause of a wiper system that only works on the lowest speed?
a. a blown fuse
b. a faulty multi-function switch
c. a loose ground at the wiper motor
d. an open park switch
B. A faulty multi-function switch
Can you explain why?
Tech A says that a replacement starter should be inspected carefully prior to installation. Tech B says the replacement starter should be bench tested before installation. Who is correct?
Both are correct. It is good practice to verify the part you are trying to install is correct, as well as making sure it functions.
This is the definition of a series circuit.
What is a circuit with only one path to ground
What is using electrical current to produce a magnetic field? Typically used to cause motion, like door locks or close the switch inside a relay.
Check here first when you have a component NOT operating.
What is the fuse or power source?
Tech A says that a fusible link will always burn into two pieces when it blows. Tech B says that a fusible link can be tested with a voltmeter without disconnecting it from the circuit. Who is correct?
Tech B is correct. A good fusible link will have source voltage on both sides, indicating it has continuity.
An inoperative light is being diagnosed. Tech A says that an open wire (circuit) between the switch and the bulb could be the cause. Tech B says that a stuck closed switch could be the cause. Who is correct?
Tech A is correct. No current can flow in an open circuit. A stuck closed switch would make the bulb stay on all the time.
This equation is the main one seen when looking at the Ohm's Law Pie Chart.
What is Voltage = Amperage x Resistance
This is a system in every vehicle that likely uses a relay.
What is the horn, fuel pump, headlights, etc.
This is the definition of a voltage drop test.
What is to see how much voltage a component or section of a circuit is consuming
Note: All the voltage drops in a circuit should add up to your source (battery) voltage!
Tech A says a battery with 6 volts at the posts is 50% charged. Tech B says a battery with 12.6 volts at the posts is overcharged. Who is correct?
Neither one is correct. A fully charged battery will show 12.6 volts, while a depleted one will show 12 volts or less.
The fuel gauge reads full at all times. All of the other instrument panel gauges work normally. Tech A says there could be an open circuit for the fuel sending unit. Tech B says the fuse for the gauges could be blown. Who is correct?
Tech A is correct. With a broken circuit, the gauge gets no change in voltage for it to read correctly. If the fuse was blown for the gauges, none of them would work, as they all receive power from that fuse.
If current (amps) goes up, this has gone down.
What is resistance (ohms)
What is to use an electromagnet to move a component in a linear (straight line) motion?
Think door lock actuators or fuel injectors!
When operating a circuit, the fuse blows immediately upon closing the switch. The most likely reason for this is...
What is a short to ground?
Tech A says that overcharging a battery will NOT cause significant long-term damage. Tech B says that in hot weather, more current will be needed to charge a battery. Who is correct?
Neither is correct. Overcharging will definitely cause long-term issues with the battery's life, and warm weather usually allows for easier charging of a battery.
A vehicle is being diagnosed for an inoperative heated steering wheel. Tech A says a faulty clockspring could cause this issue. Tech B says the steering wheel heater grid can be replaced without removing the steering wheel. Who is correct?
Tech A is correct. If the circuit for the heated steering wheel is damaged in the clockspring, it could fail to operate. Typically the entire steering wheel must be replaced if the heater grid is found to be faulty.
All circuits must have these three things to function properly.
What are Power (voltage), ground (continuity), and a load (something to consume/use voltage).
This is how relays are used when controlled by a computer or module.
What is the module provides ground for the relay control circuit, which then closes the switch to provide power to the component being operated.
Think Body Control Module (BCM) controlling the door lock actuators!
This is usually the cause of communication codes.
What is a faulty module on the CAN BUS?
A vehicle will not crank and the technician notices the interior lights do not dim when turning the key to the "start" position. Which of these is the most likely cause?
A. stuck closed starter relay
B. Loose battery cable connections
C. Starter mounting bolts loose
D. Stuck open ignition switch
D. Stuck open ignition switch. If that switch does not close, no current is sent to the relay or solenoid for the starter. This means the lights won't dim, as there is no large draw on the battery from the starter operating.
Tech A says that burned electrical connections will decrease the resistance in a circuit. Tech B says that an open switch will have continuity. Who is correct?
Neither is correct. Burned or damaged connections will increase resistance, and only a CLOSED switch will have continuity.