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2007 No crank no start

droopies

Full Member
Joined
Sep 27, 2015
Messages
20
Location
Cordova, TN
This should fall under leave well enough alone.  I have a flex fuel 5.3 2007 Avy.  Idle has been strange lately, like a momentary stall, not a miss, but it never dies.  But randomly going down road at night the headlights flicker.  I think the dash does too, but it's hard to tell.  I was reading the live data off my scan tool earlier this week and noticed the voltage was 14.1 or so, but for a split second it dropped to 11 and that's when the idled hiccuped and the lights dimmed...and when I say dim, just for a split second like A/C engaged, but the AC was off. Since it has 155k miles, I figured I'd swap the alternator.  Here's where the fun begins.  Order it from Rock auto, after verifying the code in the glove box that I have the 145A.  I disconnect the battery, R&R alternator, reconnect the battery.  WHile I am there I have wife turn key on, not crank and hold the throttle down while I clean gunk out of the throttle body.  Put the intake tube back on and try to start.  Nothing happens.  I double check battery connections about 20 times.  I then notice what works and what doesn't.  Gauges don't work..don't cycle, but the warning lights come on, then off and Check engine, stabilitrack and seatbelt stay on.  Chimes work when turning key on.  Headlights only work with key on.  Turn signals and brakes lights don't work.  Remote key fob doesn't work. Door lock button on doors don't work. HVAC controls and blower motor DOES work.  Interior lights and sunroof DON'T work.  I have an aftermarket radio.  So this morning, I left the battery disconnected all night.  I am going to swap factory radio back in, and take the batter to Autozone to test, but I am 99.9% it's good.
One weird thing, after the truck times out and powers down, which I can tell when I shut the door and wait for the HVAC control lights to go out, if I hit the key fob to lock or unlock, I hear a click/buzz in the underhood fuse panel.  I have checked fuses and relays...but I am going to check the mBEC fuse this morning.

From everything I have googled in the last 18 hours, seems like a BCM, but DAMN is it that sensitive.  I disconnected the batter at the positive, not the negative.  If that really makes a difference they should label it.  I have a simple code scanner that reads codes and live data and a multimeter.  I've been working on combustion engines since I was 10.  I have an 85 Mustang in the garage I am converting to EFI and completely rewiring under the dash, so I have a general knowledge of automotive electric systems and this is both puzzling and extremely angervating.

Any advice before I pick a dealer to take it to and spend more money that should be legal?
 
I'd check for power and good ground at BCM and PCM.  Sounds to me like something was cutting out intermittently before you replaced the alternator and in the process of moving its cabling you've changed what was intermittent to permanent.

Good news is that permanent is much easier to track down...
 
As I suspected from my basic checks and reading on the net, fried BCM.  That's actually what the service ticket from the dealer says....diagnosis fried bcm.  $930 later everything is fine, except the cruise control doesn't work at all.  I have to call them Monday and get the tech to look and see if it's simply not putting in a code for cruise control when he programmed the BCM.
 
Cruise control problem was bad brake switch.  I changed it out in about 15 minutes.  I think it was about $15 from Rock Auto.  I guess all the digging around down there to test and replace the BCM must have down it in.
 
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