GMC Hybrid No Crank / No Start / No Comm with PCM

Michael from Clinton Mobile Technician Posted   Latest  
Case Study
Driveability
2009 GMC Sierra 1500 Hybrid 6.0L (5 LFA) 4-spd (2ML70)
No Crank / No Start

So a week ago a took a little trip down to see a customer. He had a Hybrid GM Truck that will not crank or start. The shop owner stated that his scan tools would not read the Hybrid system. I took down a Tech 2 hoping we could figure out a solution. Immediately we found that there was no communication with the PCM or the Hybrid Control Systems. In looking at the schematic, it showed the CAN wires going from the Gateway to the EBCM, two Hybrid modules and then to PCM. When scoped, we found that the CAN Lo on the bus was not producing the correct waveform. We were able to communicate with the EBCM. We tried cutting out the Gateway and EBCM and going direct from an OBDII breakout to the bus with no success??? A closer look at the diagram revealed that there is a whole different network serving the PCM and part of the Hybrid controls. They are listed as PTLAN along with a wake up signal from the Gateway. With the Gateway removed we were able to get normal activity on the PTLAN network. The theory is that the protocol used is not the same as the standard CAN network. We all agreed that the problem was most likely in the Gateway as when it was removed activity went to normal. We did test for opens and shorts to ground / power. The resistance was in the high 600 + KOhm. I am waiting to hear back once the Gateway is replaced and programmed. Attached are a few pictures from the testing. I neglected to take picture of normal network comm. Have any of you run into this on a GM Hybrid?

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Geoff from Lahaina

 

Diagnostician
 

I thought this sounded familiar as something I had read before. James Avery had a Q&A style case study a while back;

members​.​iatn​.​net/forums/read/ms…

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Michael from Clinton

 

Mobile Technician
 

Nice Geoff,

The customer contacted me today and has decided the gateway is OK but the EBCM is killing the low side of network. We will see. After seeing the article you shared, I am more convinced that the gateway is bad. After sitting more may need to be replaced as well. It is going to be a project.

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Geoff from Lahaina

 

Diagnostician
 

I only deal with these on theory/paper since our lose.....ummmm, sorry, "customer" base has almost all pre-CAN vehicles, but IIRC the SDGM just allows the two networks to talk to each other. Both networks are accessible to "us" at the DLC, so unplugging the SDGM should be the confirmation.

That being said the EBCM is the most common fault, so I bet the customer allowed Google to out-vote your opinion Chris. :-)

They will learn soon enough.

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