Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum banner
1 - 10 of 10 Posts

·
Registered
Joined
·
3 Posts
Discussion Starter · #1 ·
This is my first forum post, and I am about as good with computers as I am with this car. Bear with me. The battery was running down over night. Removing the radio fuse (a 15 amp fuse in the rear fuse box) after the car has sat for an hour results in a 3.2 amp drop. This is not the whole deal though. When the PCM B fuse is removed( in the engine fuse box), it drops 1 amp more. This brings me down to .2 amps being pulled when the car is off. If you put the Radio fuse back in it jumps back up 3.2 amps but when you but the PCM B fuse back in nothing happens, but if you then start the car and turn it off with PCM B fuse in, it goes back to drawing an amp while the car is off.
I cant find the PCM B or determine whats going on for that matter. Is a .2 amp draw normal for this car when it is off( have I found all of the offending drains)? Where is the PCM B? Any other ideas?Thanks. Luke
 

·
Registered
2009 chevy
Joined
·
6,431 Posts
As you have discovered, the trucks are full of computers, including the radio.

Most of the computers remain powered during "key off". All are supposed to go to "sleep" after a defined period.

It appears that you may have a computer (or 2) that is not going to sleep.

PCM (B) is just one of the fuses providing power to the PCM (Powertrain Control Module), an other would be tagged (A).

Pulling the fuse, puts the PCM to sleep, that's why there is no current flow after re-inserting the fuse.

It looks to me like the radio is the big problem.
 

·
Registered
2006 chevy trailblazer_ls_ext
Joined
·
85 Posts
This is right out of my service manual. It is based on battery reserve capacity, divided by 4. (or, amp hour rating divided by 2.4):
"The parasitic current drain should not exceed this number. Example: If a battery has a reserve capacity of 100 minutes (60A/H), the current drain should not exceed 25 mA."

Also, it says to wait 15 minutes after the vehicle is off before testing. ("for most vehicles")

In some cases a non-fused culprit may be the cause (ie relay).

And, out of the manual directly:
"Important: Removing fuses, relays, and connectors to determine the failure area may wake up modules. You must wait for these modules to go to sleep or use the sleep function on the scan tool".

Also, there are systems that may wake up from time to time to do things, and go back to sleep, all while the car is turned off. Onstar is listed as one of them.

:)
 

·
Banned
2004 gmc
Joined
·
26,181 Posts
Some of the newer clamp-on Hall Effect ammeters aren't very accurate around 100mA, but that draw you have from the radio is certainly way too high.
 

·
Registered
2002 chevy trailblazer_ls
Joined
·
2,231 Posts
Several years ago I meaured the parasitic drain on my TB by placing a milliamp meter in series with the + lead at the battery. It was about 25 to 30 mA., (or .025 to .03 Amps) not enough to be causing my battery rundown problem. Problem I was having turned out to be a failing original Delco battery.
 

·
Registered
Joined
·
1 Posts
My abs and p brake warning lights in the dash came on although I haven't noticed any problems with my brakes p/and now my battery drains quite a bit. I have to jump it off most mornings. Could these issues be related?
 

·
Registered
Joined
·
1 Posts
I have the exact same symptoms and ran the same tests with a 2007 GMC Envoy. Was there any resolution by anyone? I had to buy a new battery today. Thanks.
 
1 - 10 of 10 Posts
Top