Lost all power, sometimes low voltage after starting.

**mechanicboy** · 01-20-2016

My 2006 Grand Prix GT lost all power today when I put the key into the ON position. Everything was dead inside and outside the car, wouldn't crank the engine either.

First, a little background. I bought the car from a guy that said it occasionally wouldn't start. I figured it was a key issue and bought the car. I cleaned the battery posts and everything seemed great. I did notice that sometimes when you start the car it reports low voltage, 10.9 on up and will stay around 11.5-12V then climb as your drive to 14ish volts.

Back to the problem I had today. I checked the battery posts first. I left the key in the ON position and started checking things out. 12.3V at the battery at the wires, on the engine(ground) and at the main connection to the power distribution box near the battery. This is wear things get weird. The bottom portion of the power distribution box had 12.3V but the top half had 9.9V. Checked the Interior fuses, a couple were 9.9 but most were 2.3 or less. When checking the voltage at the power distribution box I used the - battery post for the ground.

OK, I figured something was wrong behind the power distribution box so I decided to pull it out. I started to disconnect the battery when the terminal came loose but tapped the ground again and I heard the relays click and saw the headlights flash out. I reconnect it and everything is on. Full power to everything in the power distribution box, 12+ volts. I check the interior and still 9.9-10.1V at the fuses. I pulled the power distribution box and I didn't see anything obvious back there. No scorching, rust, corrosion. Everything was tight.

I'm worried I'm going to be chase this, so I'm hoping you guys have seen something like this before and can same me a bunch of time. Thanks in advance.

**J57ltr** · 01-21-2016

One thing that comes to mind is the ignition switch. I'll have to look at mine and see what it's reading.

Jeff

**J57ltr** · 01-21-2016

I am getting just a few tenths below battery voltage, I am reading 12.47 at the battery and 12.3 at the fuses, going by your method, key on engine off. My car is an 05'

Jeff

**mechanicboy** · 01-21-2016

The interior lights went dead too, so ignition switch doesn't make sense. Is there a primary relay/thermofuse, etc that controls the car?

**Scottydoggs** · 01-21-2016

on the tranny bell housing is the main grounds, check the other wire or two there for damage, the eyelets start to break free and cause things like this.

**NotEnoughGPs** · 01-22-2016

As I read this, one thing comes to mind and I am not surprised that ScottyDoggs named it. If you are losing power, it has to be a ground issue.
All my GP's are 6th Generation, but many of the components are the same with the '04+ GP's. When I have had any kind of power issues, I always carefully looked at the grounds and would always find a problem somewhere. The most recent case was with the negative battery post which was stripped out on mine. I see you checked the battery post already. On another GP I no longer own, it was the ground wires on the front of the transaxle (as ScottyDoggs mentioned). There was a good bit of filth from oil and coolant all around the area where the ground wires are bolted on, and upon removing them and cleaning them, I could see how there was not true contact to bare metal. After I fixed that up, I had full power back and never had problems again. (previous owner messed that car up pretty bad)
The voltages at the power distribution box will not tell you too much.
Do you know if the car was ever in a flood?
I would find and trace all the ground wires and make sure that they are intact, and are making proper contact.

**mechanicboy** · 01-22-2016

Thanks for the ideas guys, I'll check them out after work tomorrow.

In the mean time I have an update. I decided to take the car out for a drive a little over an hour ago. When I started the car to warm it up everything was fine, voltage started at low 12s but was up to mid 13s according to the display by the time I took off. Then, while about 1000' from home I tried to turn the high beams on causing the car completely lost power. Yea, it was raining too. When I lost all power everything(being the headlights, interior lights, dash lights) flashed on for less than a second several times while I coasted. Luckily there was just enough environmental light I could see the lines on the road just barely and was able to pull over. I grabbed my flashlight I keep in my car and opened the hood, opened the power distribution box and started poking around. Grabbing the lower harness closer to the fender produced results. I was able to get the power to come back on and could hear the relays clicking. I had to wiggle it a couple different ways before I could start the car and keep it running. While it was finally running I wiggled all the relays and pressed the fuses in but that didn't seem to change anything. This leads me to believe that the issue is either in the lower 1/4 block of the distribution box, in the harness coming out of the lower 1/4 or by happen-chance wiggling that harness is moving the wire that is causing the actual problem, like a ground wire.

I'll be checking ground wires in the area affected by wiggling that harness first, then will move on to tearing the harness/power distribution box apart if need be.

**mechanicboy** · 01-24-2016

So.. The ground from the battery has three wires come off of it. One to the starter, one to the chassis, one goes to a wiring harness. The two to the starter and chassis have disconnects that hold bare wire in them by a flat head set screw. The chassis wire was getting so hot that it melted the rubber protective sheath, had corroded the set screw so bad it couldn't come apart. It comes off the battery as 6 gauge wire but 8 gauge wire continues on the chassis side so I replaced the entire thing with 6 gauge. Now it starts up with 14v and goes up to 14.7 while cruising. At hot idle it's 13.7ish. I've driven it two days for over 250 miles and have had no problems with the electrical system now.