Automotive wiring diagram can be sometimes intimidating but if you know the basics and get helped by an online mechanic, you should be able to fix most common automotive electrical problems.

Automotive wiring diagram is one of the most important tools you need in troubleshooting your vehicle problem. When used correctly, it can shorten your troubleshooting time because all components of your engine are shown there. However, it seems like lots of folks are easily intimidated when using an automotive wiring diagram. A brief explanation is therefore shown here so you can use and apply automotive wiring diagram.

Testing engine computer

Like any engine wiring diagram, the entire terminal pins are shown in the diagram and the only thing to remember are the following:

Source of power supply

Usually 12 volts and mostly protected by a fuse, the wire color is usually red and must be handled with care. If accidentally touched or shorted with ignition key on, it can damage the engine computer or the components it is connected to. When testing for power supply, you can either use a digital volt meter or test light. If you are starting out, a cheap voltmeter can be bought for under $20 but if you plan to do a lot of troubleshooting, a good brand can be bought for around $50 which can have different features like testing the resistance, dwell and other functions which can help you troubleshoot faster. A test light with low impedance is also advisable so you can avoid damaging any sensors or even the engine computer. This holds true when buying the digital voltmeter also.

Tip:
When making a power supply test, always begin by testing your voltmeter or test light. This can be done by testing the battery terminals. If you have a good battery, you should get 12 volts or if you use the test light, it will light up.

Ground wire supply

Ground wire connections are usually black in color and can be tested by measuring its voltage against body frame or battery negative terminal. Max voltage reading is 0.250 volt and anything higher means a short in the system. When measuring the ground supply, connect the ground lead to a clean ground supply like the battery negative terminal or the vehicle frame. The positive lead will go to the negative supply or ground wire of the sensor or component you are testing. Ground testing is actually a good way to test if your engine computer is working because its main function is to deliver ground supply.

Tip:
When testing a ground supply of an engine component, always turn the ignition key on. When testing your engine computer, you can actually remove it completely from the system and reconnect the battery and you can isolate the wiring system for any short. With the battery connected, test the ground wires and if any reading is above 0.250 volt, you know your computer is OK.

Voltage Reference Wire

A reference voltage is generated inside your engine computer. Common value is 5 volts and could go as high as 10 volts on some engine applications. When testing, the ignition key is usually turned on with engine off and all the computer terminals connected. If you exceed the designated voltage value, it usually denotes an electrical problem either from the computer itself or one of the sensors. You can test the reference voltage quickly by disconnecting the sensors or components one at a time until the voltage reading returns to normal.

Tip:
After you disconnect any sensor or component with key on engine off, it is a good practice to disconnect the battery negative terminal after the test. This will reset the code in case it was triggered when the sensor/component was removed.

Testing sensors

Testing sensors can be made by measuring the power supply, ground and voltage reference going to it. When in doubt, it can be removed and compared readings with a new one to verify. As any engine component, they can be replaced too if they have too many hours. This goes especially to oxygen sensors which start to become lazy when used more than after 2-3 years and which can affect your fuel mileage.

Tip:
Most sensor function can be easily understood if you have a wiring diagram that will show the path of the sensor circuit.

Looking at the automotive wiring diagram as a whole is really very intimidating but if you try to isolate each circuit or individual sensor, then it is easier to solve. As long as you are a member of ATS, there will be a licensed mechanic who will assist you whenever you need help.

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