This 2004-2006 Non Hybrid GM truck network protocol DLC diagram is an example of low speed multiplex networking. This will show you how to check NO COMMUNICATION issues when this message shows up in your scanner. Using a simple tool like a voltmeter and cheap scanner,you can save yourself from paying expensive garage to troubleshoot it for you.
This 2005 GM data bus wiring above has low speed bus wire (brown color) from DLC pin 2 to various modules. This pin can be easily diagnosed using a voltmeter in minutes! You can put a voltmeter between pin 2 and pin 5 and expect to get 5 volts at KOEO. If not, disconnect each module at the bottom until the voltage returns.For more details, you can get this exact wiring diagram with correct wire colors and pin connections from your local parts stores or get it online from ATS with one on one assistance .
Before using this diagram:
1.) This diagram shows how 2004-2006 GM Non hybrid truck data bus circuit is wired together with the DLC terminals. This is only an approximate diagram.
2.) When your 2004-2005 GM Non hybrid truck has NO COMMUNICATION problem during scans, it means one of the data bus (brown) wires are shorted or one of the module or it's circuit is defective. Symptoms includes NO START, intermittent issues like stalling, occasional cutting out, etc. and no amount of scanning can help you find the problem. This will show you how to fix it using a voltmeter.
2004-2006 GM Non-Hybrid Truck DLC Diagram Description:
The low speed data bus wire is called class 2 serial bus. As you can see above, all module are wired together using a single data bus wire connected to a couple of splice bars shown as splice bars 1 and 2. Take note that the 2nd splice bar passes thru a relay before entering the other modules. The BCM module is usually utilize as the hub or gateway module. The PCM module sits on top of it. This data bus set up is common on most trucks like Tahoe, Yukon, Suburban but also used on Buicks, Pontiacs and most GM 2004-2006 vehicles.
2004-2006 GM Non-Hybrid Truck Low Speed GMLan Protocol Troubleshooting:
For the slow speed serial bus data modules, check voltage of DLC terminal Pin 2 against Pin 5 using a digital voltmeter at KOEO. To check the top left PCM Module, disconnect it from S2 red dot at splice 1 bar. A reading of 5 volts is required and any voltage reading below or higher than 2 volts means a problem on the PCM Module. This procedure is the same for the previous 2003-2004 GM vehicles including 2006 models.
Do the same test to check BCM Module at S3 connector but to isolate it, use a jumper wire as shown on dotted line above so the rest of the modules below are not cut off. You can also isolate HVAC module by disconnecting at S4 connector whereas EBCM can be isolated at S5 connector. For the splice pack 2 bar, you can isolate VCIM Module at S7 red dot connector or Rear Audio Module at S8 red dot connector. The last module that is isolated which will restore the voltage reading to normal 5 volt is the defectve module.
Note about this low speed GMLan network protocol:
On the actual bus wiring diagram, each green and red dots connector will be described using the bus wire colors and locations.
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