tomwalt

I had a noise I thought was an alternator wine. Voltages looked marginal, but good (14.6V charging, 11.8V engine off), so I pulled the 7 year old battery and charged it overnight (2 amp charge). Upon re-installation, it won't turn over (not even clicking) along with a host of other power issues.
Speedometer reads mileage, outside temp, and voltage OK, but the remaining monitored items do not indicate a reading (dashes):Examples: tire pressure, oil remaining. Inside lights and door locks don't work. Headlights will come on (bright) but won't go from low to high beam. I have 12V to the fuse box but the fusebox ground reads open (no ground at the fuse box - infinite resistance to ground but good 12Vs).
Also, Can't shift out of Park and key can't be removed. Service engine light and stabilizer lights are on - ScanGauge can't read computer (stays 'not ready').
I'm thinking no ground to the under hood fuse box = no power to a computer, but what one? The BCM holds the mileage, so it seems to be OK as well as the Radio and heater fan works so that power line is good. Any ideas would be appreciated - it's dark here now so I'll look at it tomorrow.
P.S. Wife's 1 owner car, no issues prior to this. 70K miles.

tomwalt

I replaced the battery - same indications. Followed the 12V from battery thru engine compartment fuse box to in cabin fuse box - all good. Swapped fuse box relays around. Same indications - key will go to ACC, run and start, but not to the off/remove position. With key in 'run' there is a long pause, then service engine warning comes on and odometer reads correct mileage. With key in 'start' - nothing, no clicking or anything. Xmission is stuck in Park. Windows and door locks don't work (but there is power to their fuses). Radio and heater fan work. Wipers work but don't return to home when turned off. Parking and headlights work - turn signals don't work.

tomwalt

Well - after spending the day looking at this I think the BCM may be giving me a bit of grief. I ordered a manual so I'll just work on it as I get ideas.
Battery is new and charged.
Alternator is disconnected.
Current draw is 1.6 amps with key in ACC - probably as expected.
Voltage to engine compartment and internal fuse blocks OK.
No interior lights, No door locks, no starting. Can't open rear hatch. No warning gong for key in ignition and door open. ?BCM?
But, the radio works so it could be worse.

tomwalt

I was mistaken in the original post - what I thought was the engine compartment fusebox ground was really the 12V supply line to the internal fuse box. It's a Black wire so I incorrectly assumed it was a ground.
More and more I'm thinking BCM. Does anyone know if a new BCM needs to be programmed prior to use? Do they have an internal battery to maintain memory (a volatile memory)? Can I take it to Chevy garage to be tested? Any other ideas?
Car was purchased new - this is the 1st real problem and it happened during a simple battery replacement.

in2pro

I would retrace and recheck everything you have done... it was working prior to battery replacement correct?
Have you charged up the new battery?
Do you get anything if you try to start it with the charger connected also?
I would check every fuse and relay over to make sure they are all socketed correctly...
I suspect a fuse out... and yes a new BCM will most likely need to be programmed...

tomwalt

Thank-you for the reply.
Prior to removing the original battery everything worked - just an alternator wine at 2000 RPM and 14.6 v charging voltage that would slowly decrease to 14.2V after an hour driving. Original battery so I pulled it out and charged it overnight.
Upon re-installation, nothing worked except head/tail lights, radio and heater fan. Wipers work but don't return to home when turned off.
No Interior lights, no door locks, rear hatch won't open, xmission locked in Park, etc.
Got a new battery and charged it overnight (6 amp for an hours then 2 amp trickle charge). Installed it and same indications. Starter doesn't even click - just nothing.
I'll recheck fuses and relays and make sure there is power to the BCM.
If the BCM is bad or just needs re-programed, is the Chevy garage my best bet?

in2pro

It is normal for the alternator voltage to drop as the battery becomes charged.

At any point in the process did you hook up the battery polarity backwards?
If so it may have very likely taken out the BCM and possibly other control modules....

I do not know if other shops can reprogram the BCM, but your local dealership should be able to...

tomwalt

Battery(s) were properly disconnected and reconnected. Ground removed 1st and installed last. No shorting, no big sparks, etc.
I re-checked relays for proper locations and fuses for power (both sides) - all as expected (MAS didn't have power at the fuse but not a suspect at this time).
The 'Ignition Main Relay' is the only unique relay that I couldn't test in another location. If the 'Ignition Main Relay' were to be faulty I don't understand why the interior items don't work (interior lights, tail gate, key alarm, computer calculated items) I have a manual with schematic on order. Thanks again for checking on this - you gave me additional thoughts.
The steering wheel doesn't lock (maybe because key won't go past ACC) and xmission shifter is stuck in Park. Maybe a solenoid giving a false position indication and safety ckts don't allow a start? I'll need the book to look into this as well.

tomwalt

It was the Body Control Module (BCM) - A Chevy Garage needs to install and program these. $770 - a very expensive battery charge.