2016 Auto Wiring Repair Basics for Bus Modules
Auto wiring repair on newer vehicles upto 2014 models can NOW be done quickly. Using your DLC and $21 digital voltmeter, you can save hundreds in garage diagnostic costs! This applies when testing engine computer modules which is now used extensively in your vehicle.
Shown above is a typical hook up of the voltmeter to the diagnostic link connector (DLC) when testing the integrity of auto wiring engine control module (ECM) circuits. One of the quickest way to check the wiring harness for engine computer module (ECM) is by testing the voltage of DLC pin terminals 6 and 14. These 2 pins are the communicating link or "messenger" between modules for 2008 GM vehicles. Thru these 2 pins, you can check if the communication network is active or not when you turn your ignition key on. It is active when your scanner can communicate and display the fault codes; otherwise it is not active if the codes are not shown in the scanner monitor.
With voltmeter negative lead connected to the battery negative terminal, probe terminal pin 6 and 14 one at the time with key on engine off (KOEO). Voltage reading should be in the vicinity of 2.5 volts to confirm that the link wire called data bus or serial data link is OK. Now move the voltmeter ground lead to pin 5: if you probe pin 6 against pin 5 at KOEO, minimum volt reading is 2.5 volts and 3.5 volts for maximum reading. Then moving between pin 5 and pin 14, minimum reading is 1.5 volts and 2.5 volts is the maximum.
Communicating network DLC pins terminology:
On GMLan network communication system, Pin6 is called GMlan Hi-Spd (+) whereas Pin 14 is called GMLan Hi-Spd (-)
On CAN network communication system used for Fords, Chrysler and other imports: Pin6 is called Can_H and pin 14 is called Can_Lo.
On CAN LO (pin14), anything below 1.5v is a short to ground and anything over 2.5v is short to power. On CAN HI (pin6) , anything below 2.5v is short ground and anything over 3.5v is short to power.
Shown below are some auto wiring problems attributed to a shorted/open circuit in the data bus link wires at DLC pin 6 and 14 terminals. This happens when the voltage reading you got is not the desired result of between 1.5 to 3.5 volts:
1.) Scanner no communication in your code reader or scanner
2.) Weird lights coming in your dash panel
3.) Multiple power train (P) and communication (U) codes.
4.) Poor idle rpm and engine cutting out
5.) Wiper blades suddenly coming on by itself.
6.) Cooling fans coming on at KOEF even if the engine is cold
7.) Sudden transmission going into limp mode when vehicle is stuck in low gear.
8.) Battery code B charging system failure with no communication with B codes
These all indicate that the ECM module or other modules such BCM (body control module), TCM (transmission control module) in your engine has failed.
If the reading on the DLC pins 6 and 14 are 12 volts, you have a short to the power supply wiring harness. Whereas if you get 0 volt reading on those pins, the short is coming from the ground. To verify if you have a short in the ground side, move the negative lead of the voltmeter from the negative to the positive post of the battery. If it now shows that the voltage reading is 12 volts, then the short is coming from the ground wires.
Finally, this is just one example of auto wiring repair which you can do using your DLC terminal pins and a cheap $21 voltmeter which you can buy from Amazon. To bring your vehicle to a dealer because your scanner will not communicate with your vehicle and charge you $100 an hour for testing does not make sense anymore.
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