SHVCS Paired with Low Ambient temperature
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Background, I bought the car broken. Because I'm a glutton for punishment 
. I haven't owned a volt before so I'm scouring the forum here, great resource thank you! But wanted your opinion.
Doesn't run, and I don't have a clear story on what happened. Looks like both front corners have been hit to some extent (aluminum behind bumper cover has some squish to it).
I have 6 messages on the dash when I turn the car on. Including -40 temp outside (be careful there could be ice), low voltage charging system, high voltage charging system, power steering system, and I think the others were doors being open that I wasn't worried about.
I'm not worried about low voltage and power steering, I figure those are from the 12v battery having gone dead and high voltage not kicking on.
Odd #1: I tried connecting using a bluetooth obd2 to my phone and I can't get the car to talk. I have power as the adapter lights up.
Odd #2: I swapped the ambient air temp sensor located on the passenger side just behind the bumper cover with a 15k resistor. This doesn't fix the "-40" showing on the infotainment screen. I checked pins 26 and 40 on the computer under the passenger seat and I get 15k ohms, so it seems the wiring is good there. I purchased the alldata subscription so I can look up any other wiring/data as needed.
Odd #3: If I remove all 12v power from the car and re-apply all the same codes are there, car won't charge (orange light on dash under front window). Engine doesn't even start.
I tried booting the car without the module under the passenger seat. Only difference is the shvcs warning went away, all the other warnings stayed the same.
My current thought is the computer under the passenger seat is bad, as there is apparently some communication happening but it certainly isn't reading the ambient temperature sensor. And this is the same computer that reads the battery coolant level and presumably allows the high voltage battery to come online.
I did order the vcx nano and will be setting up a VM on my laptop to see if it connects but my hopes aren't high if I can't even get standard codes out of the car.
Any thoughts or opinions? I know that's a lot of information to dump so thank you anyone that's still here at this point. My concern with grabbing another computer for under the seat is would that actually fix the communication over OBD2. That's one I haven't been able to pin down.
Thank you!
. I haven't owned a volt before so I'm scouring the forum here, great resource thank you! But wanted your opinion.Doesn't run, and I don't have a clear story on what happened. Looks like both front corners have been hit to some extent (aluminum behind bumper cover has some squish to it).
I have 6 messages on the dash when I turn the car on. Including -40 temp outside (be careful there could be ice), low voltage charging system, high voltage charging system, power steering system, and I think the others were doors being open that I wasn't worried about.
I'm not worried about low voltage and power steering, I figure those are from the 12v battery having gone dead and high voltage not kicking on.
Odd #1: I tried connecting using a bluetooth obd2 to my phone and I can't get the car to talk. I have power as the adapter lights up.
Odd #2: I swapped the ambient air temp sensor located on the passenger side just behind the bumper cover with a 15k resistor. This doesn't fix the "-40" showing on the infotainment screen. I checked pins 26 and 40 on the computer under the passenger seat and I get 15k ohms, so it seems the wiring is good there. I purchased the alldata subscription so I can look up any other wiring/data as needed.
Odd #3: If I remove all 12v power from the car and re-apply all the same codes are there, car won't charge (orange light on dash under front window). Engine doesn't even start.
I tried booting the car without the module under the passenger seat. Only difference is the shvcs warning went away, all the other warnings stayed the same.
My current thought is the computer under the passenger seat is bad, as there is apparently some communication happening but it certainly isn't reading the ambient temperature sensor. And this is the same computer that reads the battery coolant level and presumably allows the high voltage battery to come online.
I did order the vcx nano and will be setting up a VM on my laptop to see if it connects but my hopes aren't high if I can't even get standard codes out of the car.
Any thoughts or opinions? I know that's a lot of information to dump so thank you anyone that's still here at this point. My concern with grabbing another computer for under the seat is would that actually fix the communication over OBD2. That's one I haven't been able to pin down.
Thank you!
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Ah yes, I did miss that part! I have a lithium 12v as the battery right now, with a trickle charger running to keep the voltage up. So that begs a question, if the 12v system is getting a good 13v from my battery, should it be throwing a power steering error? I could understand the low voltage charging error since there isn't a high voltage source for that module to operate.
It's a 2013 model year.
I think the steering is 12V, so I agree with you. Put your multimeter on the battery and see if it is holding 12.6V minimum on start-up.
I think the module under the passenger seat is the HPCM2. I doubt anything will work if it isn't connected.
I think the module under the passenger seat is the HPCM2. I doubt anything will work if it isn't connected.
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I'll watch the voltage as the car is booting next time to see if it dips. Certainly sitting at 13+ once the car is "running". I actually tried booting the car without the HPCM2 connected (module under the passenger seat) and it had less errors ironically. The high voltage charging system message wasn't there.
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My VCX came in quicker than expected! It seems I have communication issues. I can get to a few modules but most aren't talking!
I'd copy and paste the whole thing but it's in a VM so more difficult than it should be. I noticed that none of the modules in dlc pins 6,14 are communicating. I think I need to pull up a diagram and see what those look like. Maybe I have a short or bad wire on that bus?
Here are most of them:
![Font Number Parallel Screenshot]()
I'd copy and paste the whole thing but it's in a VM so more difficult than it should be. I noticed that none of the modules in dlc pins 6,14 are communicating. I think I need to pull up a diagram and see what those look like. Maybe I have a short or bad wire on that bus?
Here are most of them:
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Ok I did some reading on canbus troubleshooting. I’m getting 2.2ohms from pin 6 to pin 14 on the OBD connector. Sounds like I have a short! Also low resistance 6 to ground. I get 13v from car positive to pin 14.
Unplugged ecm And the one under passenger seat. No change. Need to get access to more computers to see if one is causing the short. Or if it’s in the wiring. From what I understand I should get 60ohms not 2.
Unplugged ecm And the one under passenger seat. No change. Need to get access to more computers to see if one is causing the short. Or if it’s in the wiring
. From what I understand I should get 60ohms not 2.
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I'm stumped!
I did some electrical troubleshooting. Found the brake controller and unplugged it. Also found the BCM and unplugged it. Using connector x6 pins 24/25 at the BCM I tested continuity back to the obd2 plug pins 6/14. With the car off I have continuity on the can+ and can- lines as expected. However with the car on each also has continuity to 12v+ (pin 16 on the obd2 connector).
The one module I couldn't find was the telematics. It's supposed to be right next to the BCM but it ain't there! Maybe this car didn't have bluetooth/onstar? It does have an onstar button though. Or maybe they stuck that module elsewhere and it is in fact my problem!
The reason I went for the brake controller and the BCM is they are the first modules after the obd2 plug. So theoretically unplugging those opens up the circuit entirely. But it's not. I think I'll have to put my head under the dash more and look for antenna wires to see if I can find the telematics computer...
I did some electrical troubleshooting. Found the brake controller and unplugged it. Also found the BCM and unplugged it. Using connector x6 pins 24/25 at the BCM I tested continuity back to the obd2 plug pins 6/14. With the car off I have continuity on the can+ and can- lines as expected. However with the car on each also has continuity to 12v+ (pin 16 on the obd2 connector).
The one module I couldn't find was the telematics. It's supposed to be right next to the BCM but it ain't there! Maybe this car didn't have bluetooth/onstar? It does have an onstar button though. Or maybe they stuck that module elsewhere and it is in fact my problem!
The reason I went for the brake controller and the BCM is they are the first modules after the obd2 plug. So theoretically unplugging those opens up the circuit entirely. But it's not. I think I'll have to put my head under the dash more and look for antenna wires to see if I can find the telematics computer...
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Ok so I did find the telematics module. It was on the drivers side left of the brake pedal!
however what I found is that if I left telematics and bcm plugged in but the x1 plug of the bcm unplugged to prevent any other computers being on the bus I could put a 60ohm resistor across pins 6/14 of the OBD connector and read the bcm!
next computer in the line is becm which seems to be part of the battery thoug. Tried disconnecting the battery charger and hybrid controller module 2 which didn’t help. So I’m fairly certain it’s either wiring between bcm and becm, or it’s the becm itself.
What makes it worse is that the second string of computers that starts with the electronic brake controller is also bad. I have to leave the ebcm unplugged. Haven’t found the Hvac plug to isolate the ebcm for sure.
I’m wondering if someone reversed some jumper leads or lightning hit this thing and blew multiple computers at once.
however what I found is that if I left telematics and bcm plugged in but the x1 plug of the bcm unplugged to prevent any other computers being on the bus I could put a 60ohm resistor across pins 6/14 of the OBD connector and read the bcm!
next computer in the line is becm which seems to be part of the battery thoug. Tried disconnecting the battery charger and hybrid controller module 2 which didn’t help. So I’m fairly certain it’s either wiring between bcm and becm, or it’s the becm itself.
What makes it worse is that the second string of computers that starts with the electronic brake controller is also bad. I have to leave the ebcm unplugged. Haven’t found the Hvac plug to isolate the ebcm for sure.
I’m wondering if someone reversed some jumper leads or lightning hit this thing and blew multiple computers at once.
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