This 2005 GM hybrid truck network protocol DLC diagram is an example of high 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, you can fix this problem and avoid paying expensive garage to troubleshoot it for you.

GM hybrid truck bus network


Before using this diagram:

1.) This diagram I made myself showing how 2005 GM hybrid truck data bus circuit is wired together with the DLC terminals. This is only an approximate diagram as I see it.

2.) When your 2005 GM hybrid truck has NO COMMUNICATION problem during scans, it means one of the low speed data bus wires (yellow color) is shorted or one of the modules 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.

2003 GM Hybrid Truck DLC Diagram Description:

Shown above is the DLC wiring diagram of the data bus network of a 2005 GM Silverado Hybrid Truck. Starting this model year, GM introduces the high speed data bus networking. This networking protocol has the fastest speed when compared to previous years. However, this protocol is only available only on GM hybrid truck models excluding all other trucks like Tahoe, Yukon, Suburban which were still using the slower Class 2 serial data bus networking.

This diagram shows both low speed and high serial bus data combined together (brown and green wires). The low speed bus dot connections are shown on all the modules on the left (yellow wires) with Red dots color connected to both splice pack 1 bar and splice pack 2 bar connectors. You will also notice slow speed serial data bus has only 1 single bus data link instead of 2 for high speed serial data bus shown on the right. These 2 high speed bus wires are twisted to prevent radio frequency interruptions (RFI).

High speed serial data bus protocol is called High Speed Serial GMLan by GM but otherwise called CAN High Speed network protocol by other makes of vehicle.

According to GM, Pin 6 is called GMLan Serial Data Link (+) bus wire (brown color) whereas Pin 14 is called GMLan Serial Data Link (-) bus wire (green color).


2005 GM Hybrid Truck Hi 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 previous 2003-2004 GM vehicles including 2006 models.

Do the same test to check BCM Module at S3 connector, HVAC Module at S4 connector. For the splice pack 2 bar, you can test VCIM Module at S7 red dot connector or Rear Audio Module at S8 red dot connector.

Note about THIS PCM Module:

There will be 3 bus wires connected to it as you can see here. One slow speed connection (black dot) at S2 in top left and 2 speed bus connectors shown by 2 green dots at PCM on top right. You can get the exact wiring diagram from your local parts store or get it FREE from ATS if you are a member.

To test GMLan high speed bus network, set your voltmeter at ohmmeter range and measure resistance between DLC terminals Pin 6 and Pin 14. Do this test at key on engine off and expect to get 2.5 volts. Then reset your voltmeter range to MINMAX setting so you can test resistance at key on engine off (KOEO). The voltage reading should fluctuate between 1.5 to 3.5 volts. You need these voltage readings to verify if the modules are communicating. If not within this range, modules will not communicate resulting in NO STARTS and other weird problems. Your scanner will not work and give you NO COMMUNICATION message.

To find which high speed module is responsible, starts disconnecting each modules like PCM, HCM, HPS, GCM and ESCM shown on the right of the diagram. You need to disconnect them at green dots on each module. The last module you touch that restored the voltage fluctuation is the culprit.

Note about this high speed GMLan network protocol:

On the actual bus wiring diagram, each green and red dots connector will be described using wire color and location. Above diagram is for demo purposes only. Also please remember that this diagram applies to 2005 GM hybrid truck only.

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