I messed up bad on my 2008 convertible. My battery was dead and I jumped it from a golf cart. Instead of the 12v end of the battery bank I used the 48v end. Everything went dark. No dash, no lights, no ignition and on and on. I checked the fuses but only the horn, fog lights, radio/Vic's, and phone were blown. I was amazed none of the fusible links blew. I bought a used BCM and swapped it out. I have not had it flashed yet but I got back most functions including the ignition switch, door locks etc. still no dash, top or starting. The radio and phone fuses still blow when replaced. Will flashing the BCM resolve some of these issues? Will the diagnostics even work? What should be the next test procedure? Thanks

 

Yikes sorry to hear about your mishap. From previous experiences if a rectifier (semi-conductor or diodes) blows due to wrong polarity or over voltage they usually fail in 2 common ways, they go open circuit or a dead short. Your problem with it still blowing fuses after the fact could be shorted rectifiers or diodes in the circuitry or components.
By Phone fuse are you referring to OnStar? If so you could try unplugging the module to see if it still blows the fuse. The module is usually located on the other side of the compartment liner in the trunk right hand floor compartment.

 

Yes, Onstar fuse keeps blowing. I will try your suggestion. If I unplug on star does it also disconnect the gps used in the nav system. You raise a good question, are there diodes in the engine compartment fuse box and how do I test them?

 

Depending on how deep you are willing to go with this issue it might be worth your while investing in a factory set of manuals. I purchased mine from Zip Corvette last year. Being a mechanic I have always purchased a set of manuals for every car that I've owned. The electrical section has all of the schematic diagrams for every system in the entire car, the pin out for all of the plug connections, the component layouts, locations and harness routing. It's an invaluable resource if you have a complex issue to diagnose.

I'm a relative Corvette newbie having only acquired ours last November just in time to put it in 5 months of winter storage but I am a retired mechanic of 45+ years. I can't speak for Corvette regarding diodes in the system but would be very surprised if there weren't any since I have encountered lots of them in many applications and manufacturers, some were in line as part of a harness and some were even encased in a plug in adapter or looked like a regular harness plug being encased in plastic. To the best of my knowledge the OnStar and NAV radio are interconnected. I found that out by investigating getting rid of the overpriced and marginally practical telephone service of the OnStar system and replacing it with a Blue Tooth hands free device to link your own cell phone to the cars sound system, microphone and phone buttons. I found that if I install a BlueStarII device that I looked into, the voice recognition feature of the NAV no longer works since that feature is handled by the OnStar module. As far as testing a component that blows fuses, unplugging the device should confirm whether the unit has an internal short or whether the problem is elsewhere.

A diode only allows current to flow in one direction which is easy to test with a multi-meters continuity test. If it conducts in both directions its shorted out and if it doesn't have continuity in either direction it is open circuit.

Good luck with your project, I don't envy your challenge.

 

There are 3 diodes located inside the fuse block, under hood location.

 

Yes, only one is identified in my diagram does your shop manual show the purpose of all three? Does it show if the dash cluster is controlled by a module, the heads up display lights but none of the dash. How expensive is the shop manual?
Thanks

 

Sorry to hear about the 48V -12V mishap. It's hard to tell what damage was done by this configuration. I have attached the 4 schematics for the under hood fuse box. You can look at these but it's really hard to tell what could have got damaged. Typically an overvoltage will damage sensitive electrical components downstream.

Maybe these will help, maybe not. I've looked in the manuals for overvoltage incidents, but there is no troubleshooting guides, or places to look for damage in the manuals.

Here are some schematics.

 

The 2008 factory GM manuals from Zip Corvette are $270. If they are the same as mine for a 2007 it is a 4 volume set and each volume is like a big city telephone book in size shipped in a box that probably weighs close to 20lbs. For some reason the 2007 manuals were $60 cheaper than those on on either side.

 

I replied yesterday but it did not post, I am new to this. Thank you both. The schematics help. The diodes are related to the delay wiper circuits. When I continuity test them I have no continuity in either direction. I would suppose that to be normal. I do not have a diode tester function on my VOM.

 

This may help you with the diode testing, at the bottom of the page for resistance testing.
http://en-us.fluke.com/training/trai...ultimeter.html

 

I do not have a diode mode on my VOM. Based on no resistance in either direction using the resistance test I would assume all three diodes are blown. This would not surprise me as the wiper variable speed is not working. Thanks for the reference.

I am still looking for the ONSTAR module. Not in the back or above the fuse block/BCM. Anyone know where it is on a 2008 convertible?

 

Unless you have a Z06 your OnStar Module is in the same location as my 07 Vert. You have to remove the cargo area floor liner then the lid and liner of the passenger side floor compartment. The OnStar module is attached to the foreword face of the compartment and is covered by the compartment liner. In a Z06 the battery is in that compartment and having an electronic module in close proximity of the battery is a bad idea so they moved it under the dash on a Z06.

The other image I provided is for illustration purposes only of a Bosch relay to show you the many likely places you would find diodes in the system. Diodes are commonly used inside relays in place of a capacitor to absorb the induced voltage spike that occurs when a circuit in a coil of wire is interrupted. An ignition coil sends a spark to the plugs when the power is interrupted, not when it is powered up. These induced voltage spikes from coils of windings can cause a lot of problems in voltage sensitive solid state components. You can see by the schematic that if the diode was shorted it would provide a path of least resistance causing a short to ground and preventing the relay from energizing.

Diodes are also commonly used in circuits that can be powered from multiple sources while isolating other devices in the system without having it back feed and send power to other devices in a circuit.

Switching in most modules and components is accomplished with solid state devices so its a crap shoot as to what got damaged. I've seen a lot of damage done over the years to solid state systems, for example on forestry machinery that was struck by lightning. When computer controlled systems were introduced in the 1990's we learned a hard lesson early on by electric welding on machinery. Strike an arc to weld on a bracket or fix a crack and suddenly the engine or machinery is non operational since you just blew up a $2,000 ECM or Hydraulic Control Module. In order to prevent these mishaps we got in the habit of disconnecting the batteries and unplugging the computer modules before electric welding on modern machinery.

I hope this info helps and leads you in the right direction.

Cheers

 

Thanks, ordered the manual. All I can do is pick away at one problem at a time. Hope to get it towed to the dealer to program the BCM next week. Will look for the Onstar tomorrow.

 

The final result.
Hopefully this helps someone else. In an overcurrent situation, we ultimately replaced the BCM, ECM, Onstar module, Brake module, Nav/radio, convertible top module, dash board and air bag module. Everything is back to new.

 

Ouch, that was an expensive mistake but I'm glad you have your car back in operation. Your experience reminds me of the mess I encountered with computerized forestry machinery that was struck by lightning and it fried most of the electronics.