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Discussion Starter · #1 ·
I went to start my 2007 GMC Sierra Crew Cab 6.6L Turbo Diesel on Sunday after it sat for about 10 days and when I tried it acted like it had a dead battery. It just made one click and then nothing. I disconnected the main battery and put it on a charger for about two hours and then reconnected. I then tried to start the truck and still nothing. the instrument panel lights worked but they flickered repeatedly. The headlights worked and the radio worked on AM & FM but when I selected XM the radio said "Theftlock"

At this point I tried disconnecting each of the two batteries negative terminal one at a time and tried to start on each battery separately with the same results. I had the truck towed to my mechanic who pulled both batteries and charged and load checked them and they checked good. Since my mechanic was at a loss he had the truck towed to an Auto Electrical repair shop. They told me one of the batteries seemed to be shorted internally and that when I tried to start the truck it somehow caused the Body Control Module and the computer (PCM) to be damaged. They couldn't figure out what had happened but it ended up costing $953 for 2 new batteries, a new Body Control Module (BCM) and a re-manufactured PCM. Their bill said "Car shorted out BCM and PCM don't know how - vehicle does not have any short"

So if I accidentally leave the lights on or use the radio for an extended time and run down the batteries I should expect to cause $1000 damage to the electrical system when I try to start my truck?? My concern is that no one (not my mechanic or the Auto Electric repair shop) could determine what actually happened?? This gives me pause and makes me nervous that it could happen again. When I last drove the truck (about 10 days prior) there was absolutely no indication, not the volt gauge, no check engine, no low battery indication on the DIC nothing, not one inkling that anything was wrong.

Since no root cause could be found I am concerned it could happen again. The truck only has 80,000 miles and I had hoped to keep it forever however now I am not so sure. Does anyone have a clue as to what could have caused this? Has any one seen anything similar?
 

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A few thoughts on what happened
first if a batt is shorted inside (not uncommon) you can NOT charge it to full 12.5+V as a shorted CELL will not contribute to the voltage output and secondly I have a hard time believing a shorted battery killed your BCM and engine ECM
I would suspect more likely incorrect charger usage/high voltage was applied IE like a REVOLT system would cause the ECM's to be damaged

to test a battery for a short charge it with a normal battery charger until draw current drops off and or charge voltage starts to rise (depending on charger style)
and disconnect charger and check the batts VOLTAGE after one hour and should be over 12.5V and upwards of 12.8V of NOT shorted but if shorted the charging voltage/current draw will NOT rise/drop
and the standing voltage will be 10.5 to 11V range

also if it was below freezing when your truck was parked and dies the batteries may have frozen inside which will prevent the battery from accepting a charge during your initial attempt to start
 

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Discussion Starter · #3 ·
A few thoughts on what happened
first if a batt is shorted inside (not uncommon) you can NOT charge it to full 12.5+V as a shorted CELL will not contribute to the voltage output and secondly I have a hard time believing a shorted battery killed your BCM and engine ECM
I would suspect more likely incorrect charger usage/high voltage was applied IE like a REVOLT system would cause the ECM's to be damaged

to test a battery for a short charge it with a normal battery charger until draw current drops off and or charge voltage starts to rise (depending on charger style)
and disconnect charger and check the batts VOLTAGE after one hour and should be over 12.5V and upwards of 12.8V of NOT shorted but if shorted the charging voltage/current draw will NOT rise/drop
and the standing voltage will be 10.5 to 11V range

also if it was below freezing when your truck was parked and dies the batteries may have frozen inside which will prevent the battery from accepting a charge during your initial attempt to start
Richmond 2000,

Thanks for the reply. I agree with you an internally shorted battery or a drained (dead battery) should not cause the damage to the BCM and PCM. Unfortunately I do not have the batteries or I would test them further because they wanted the core turned in. As far as incorrect charger usage that didn't happen. I was the only one who hooked up the battery charger and I absolutely guarantee that it was done properly. That was the only "system" hooked up externally to the truck a battery charger, I don't even know what a "REVOLT" system is??

Again, my biggest concern is I have no root cause so I cannot know what to do in the future to prevent it happening again.

I drove the truck today to work and it seemed to work fine. Since I was paying particular attention to the volt meter I noticed that that it read around 12V when I had the key on before I started the truck and then went down to about 10-11 Volts after I started the truck. After 20-30 seconds the volt meter went up to what I would expect around 14 volts and stayed there while I was driving. I tried this twice today and my observations were the same.

BTW I live in California so it never was below freezing.

Any other thoughts are appreciated.
 

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Richmond 2000,

Thanks for the reply. I agree with you an internally shorted battery or a drained (dead battery) should not cause the damage to the BCM and PCM. Unfortunately I do not have the batteries or I would test them further because they wanted the core turned in. As far as incorrect charger usage that didn't happen. I was the only one who hooked up the battery charger and I absolutely guarantee that it was done properly. That was the only "system" hooked up externally to the truck a battery charger, I don't even know what a "REVOLT" system is??

Again, my biggest concern is I have no root cause so I cannot know what to do in the future to prevent it happening again.

I drove the truck today to work and it seemed to work fine. Since I was paying particular attention to the volt meter I noticed that that it read around 12V when I had the key on before I started the truck and then went down to about 10-11 Volts after I started the truck. After 20-30 seconds the volt meter went up to what I would expect around 14 volts and stayed there while I was driving. I tried this twice today and my observations were the same.

BTW I live in California so it never was below freezing.

Any other thoughts are appreciated.
some low cost chargers do NOT rectify the mains A/C power well and that can DAMAGE the ECMs
a "REVOLT" is a jump start system on tow trucks or in Garages that can put out 18V at the press of a button (to be done while the engine is being cranked ONLY)

one thing to get tested is the rectifiers in your alternator and a shop like NAPA or PEP boys will usually offer free alt testing if the rectifier is "leaking" it will cause part A/C power to be introduced which can damage ECM units and damage batteries + cause the batteries to go dead while parked for an extended time

is your truck the NEWER or OLDER style as 07 BOTH versions where in production (does yours look like a 2012?)

if it is the NEWER style the fuse panel on the Left side of the engine compartment can be pulled upwards and that unplugs a large plug under the fuse panel and might cause damage if done or was loose while the truck ignition was in the run position

I would check the wiring between the batteries and the alternator and to the starter and where it auctions of to go to the fuse panel

I am also curious how the electric shop determined the ECM/PCM was at fault because I do not know of ANY scan tool outside of a TECH2 that GM charges a LARGE licence fee that would interact close enough to determine individual ECM's and wonder how much it was a "throw parts at it" until it started
and yes all those parts would have a "CORE" and would go back to the supplier/ the BATTS have a value for recycling and/OR MUST be returned (I do NOT live in California or even the USA)
 
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