2008 Tahoe Hybrid parked & 30 minutes later NO START...AAA called for jump...No start...Flatbed tow called...more powerful jump start...NO START...Towed home...Next day called to tow to dealer...Driver tried 2000amp jump start and it started...Drove to O'Reilly's Auto parts...w/engine check light on...Which disclosed two p-codes..."DTCPOAC4=Hybrid Powertrain Control Module Requested MIL. Illumination? With engine on...This code is a Type A DTC"...SECOND CODE was DTCP16F9...Indicating Control Module Shutdown Performance...THIS WAS ALL GREEK TO ME...Spent hours going from dealer to repair shops w/o turning vehicle off...finally went home figuring I had to bite the bullet & tow to Dealer...AGAIN shut engine down and left overnight...Next morning went out...The vehicle started up AND THE CHECK ENGINE LIGHT WAS GONE...Lo & Behold it has started for the next three days??? NOW WHAT? I had my 12v car battery checked and IT is good??? Is there an alternative besides the dealer to diagnose and repair as needed, since I have nothing other than the "trouble codes from O'Reilly" to show...Disaster waiting to happen!!! I just can't ignore till it happens again??? I'm a disabled 86 year old dude...w/mixed emotion about 'FREE' advise but still ask for Your best shot! thanks..Bobby

 

there's a lot of conflicting information about how to jump start these trucks. from what I can tell, the hybrid battery powers the front electric motor inside the tranny, that spins the engine over to crank it. it has no normal 12v engine mounted starter.

the owners manual I have say the truck will jump start off the 12v battery, I'm guessing by it feeding power to the big hybrid battery that would take time on a charger, not a quick jump start like normal, (I'm guessing) which might explain them needed some super jump box. but I've also read either on here or another site that only a dealer level scan tool can put it into a mode that allows the hybrid battery to be changes without the engine running.

if you can find a dealer that has a tech trained in hybrids, that might be your best option. I remember when my volt had a relay go bad still under warranty, they told me only one tech was trained on them and he was out for a few days. so they gave me a rental till he came back. you might call a few local dealers and ask if they have a tech that's good with these trucks. I'm guessing that 2nd code will mean something. but not sure what without access to dealer level stuff. or at least a good amount of time Googling it.

as for if it will happen again. I don't know enough about these trucks to offer an opinion.

 

replace the 12v battery cables and you will be good. The 12v battery turns on all the Hybrid modules and if power from the 12v is intermittent your +300 volts from the hybrid battery means NOTHING!