Battery drain - cause?

99Yak · Apr 3, 2020

I know this is my first post and I may not be following protocol. I hope I don't get run off.

I had the same issue with my 99 burb. A friend (owner of a large repair shop) told me to get a new CD player. I did. Never had the problem again - 5 years. Unplug yours - what could it hurt?

Notes:
I have no explanation because he never offered one
He never looked at the vehicle
CD player was functional
CD player was factory and I replaced it with factory reman
We use it as an RV, so it sits for long periods of time
Sounds too simple. It did to me too.

HotWheelsBurban · Apr 4, 2020

There should be a wire that goes to the radio that's hot all the time to run the clock, it might also go to the CD player, IIRC the CD player will accept or eject discs if the ignition isn't on. Not sure because mine hasn't worked for a while. If I'm right about this, the CD player might be where the issue is. If it happened to 99Yak's truck, could be something that they do with age. 20 year old circuit boards do funny things....good luck! Let us know if that is indeed the problem or whatever it turns out to be

Pinger · Apr 6, 2020

Got some time with it today so (maybe) a little further on.
Disconnected alternator entirely ie, the big lead that goes to the battery and the plug (only one wire) that I didn't know was there. No difference. Are they the only connections on the alternator?

Disconnected the cassette player (no fancy CD players here!) and no difference. Found the permanent live feed and when I disconnect the battery and test for continuity between it and ground I'm getting a reading on the MM (and a 'bleep'). To my mind, that lead should have no resistance - correct?

I have fuses in the door jamb and another lot in the Fuse Relay Centre. Are there any more fuses on a Suburban? (Haynes talks of a fuse box under the dash - pick-ups only?)

Pinger · Apr 7, 2020

A bit more done today.
All clear between the radio/cassette and fuse#19 located in the door jamb.
Fuse#19 is the permanent live from the battery to the RC. The power comes in on the upper contact. With the battery disconnected I'm seeing 5 Ohms between that connection and ground. Can someone please confirm that that shouldn't be happening?

Pinger · Apr 27, 2020

Back to this - with a reliable MM (Multi Meter) and the fuses that affect (ie lower) the current draw are in the FRC (under hood) the big 50A battery fuse and the 20A fuse that is marked ECM B which according to handbook protects 'fuel pump, PCM/VCM'.
What is PCM/VCM?

If I'm reading the MM correctly I have a 15.2mA draw. Removing the 50A fuse reduces it to 10mA, removing the 20A reduces it to 6mA. Both fuses removed together takes the draw to 1.2A.

15.2mA should be acceptable but it does flatten the battery in a week. Also, when I first connect the MM it goes to overload for a second or so, then shows 80mA for a few seconds before settling to 15.2mA.

The other observation is that in the fuse 'box' in the door jamb, pulling the big (metal bodied) fuse A (Power door lock, 6-way power seat (not present on my truck), Keyless entry module) as I refit it, I can hear clicking from behind the dash in the vicinity of the gauges/lighting switch.

Something else I noticed at the weekend. The 'dome override' works for the front door but opening a rear door lights up the rear dome - normal?

Preliminary findings from today and I can't say accurately if removing fuse A affects the current as I think I've blown a fuse on the mA circuit of the MM - which was due to that highish initial current tripping it into overload.

Can anyone identify what PCM/VCM is and/or make sense of all the above? (OK, I'll settle for identifying PCM/VCM!).

HotWheelsBurban · Apr 27, 2020

Pinger said:
Back to this - with a reliable MM (Multi Meter) and the fuses that affect (ie lower) the current draw are in the FRC (under hood) the big 50A battery fuse and the 20A fuse that is marked ECM B which according to handbook protects 'fuel pump, PCM/VCM'.
What is PCM/VCM?

If I'm reading the MM correctly I have a 15.2mA draw. Removing the 50A fuse reduces it to 10mA, removing the 20A reduces it to 6mA. Both fuses removed together takes the draw to 1.2A.

15.2mA should be acceptable but it does flatten the battery in a week. Also, when I first connect the MM it goes to overload for a second or so, then shows 80mA for a few seconds before settling to 15.2mA.

The other observation is that in the fuse 'box' in the door jamb, pulling the big (metal bodied) fuse A (Power door lock, 6-way power seat (not present on my truck), Keyless entry module) as I refit it, I can hear clicking from behind the dash in the vicinity of the gauges/lighting switch.

Something else I noticed at the weekend. The 'dome override' works for the front door but opening a rear door lights up the rear dome - normal?

Preliminary findings from today and I can't say accurately if removing fuse A affects the current as I think I've blown a fuse on the mA circuit of the MM - which was due to that highish initial current tripping it into overload.

Can anyone identify what PCM/VCM is and/or make sense of all the above? (OK, I'll settle for identifying PCM/VCM!).

PCM: Powertrain control module
VCM: Vehicle control module

RawbDidIt · Apr 27, 2020

PCM/VCM should be (somebody correct me if I'm wrong) the power train control module, commonly referred to as ECM. With the first connection causing such a draw, it sounds like it may be a capacitor. If it is discharging, then as soon as it gains access to more juice it'll pull current pretty quickly to recharge. If it's not able to keep its charge, it may do this once discharged and pull higher currents than you're seeing at rest. This would point me to aftermarket loads on the sytem including amplifiers, head unit, etc. What do you have aftermarket in there besides the fuel system? Car alarm? Sound? Anything?

Sent from my SM-N976V using Tapatalk

HotWheelsBurban · Apr 27, 2020

Just re read your post. The dome light override is supposed to work on all 6 doors (2 on each side and the 2 barn doors out back). Maybe you have a problem in the headlight switch, or a pin switch in a door jamb that's not working properly. I'm having a little trouble with the big door pin switch on the right rear door, but I think it's probably just dirty and old. The downside of your truck having such low mileage is that it's been sitting most of its life, in cold, humid conditions to boot. That's not the kind of weather that electric components like. Not much you can do about it, but that's how they are. Hope this helps

Pinger · Apr 27, 2020

HotWheelsBurban said:
Just re read your post. The dome light override is supposed to work on all 6 doors (2 on each side and the 2 barn doors out back). Maybe you have a problem in the headlight switch, or a pin switch in a door jamb that's not working properly. I'm having a little trouble with the big door pin switch on the right rear door, but I think it's probably just dirty and old. The downside of your truck having such low mileage is that it's been sitting most of its life, in cold, humid conditions to boot. That's not the kind of weather that electric components like. Not much you can do about it, but that's how they are. Hope this helps

I think you might be right.
I used the dome override when I was last checking electrics and I had difficulty in getting it to latch. Once I did it was doing what it should - until Saturday and I opened a rear door and the light above the rear seats came on....

Pinger · Apr 27, 2020

RawbDidIt said:
PCM/VCM should be (somebody correct me if I'm wrong) the power train control module, commonly referred to as ECM. With the first connection causing such a draw, it sounds like it may be a capacitor. If it is discharging, then as soon as it gains access to more juice it'll pull current pretty quickly to recharge. If it's not able to keep its charge, it may do this once discharged and pull higher currents than you're seeing at rest. This would point me to aftermarket loads on the sytem including amplifiers, head unit, etc. What do you have aftermarket in there besides the fuel system? Car alarm? Sound? Anything?

Sent from my SM-N976V using Tapatalk

I guessed (but didn't want to believe) that PCM could be the Power Control Module. Was clueless re the VCM.
There's nothing aftermarket apart from the LPG (which I'm confident isn't the problem) and a weird set-up for the gauge backlighting. There is an additional switch (which changes the colour of the lighting) and a pot - so two methods of dimming. I had a good look at all that and couldn't find anything amiss.
What's making things more difficult is that on the 10A range the MM isn't sensitive enough to pick up small changes and when set to 200mA range that current spike blows its fuse.
Your description re capacitor sounds (very) plausible.
The other non-standard set-up - but not aftermarket as such is the external lighting system. It doesn't (just dawned on me - I haven't actually checked this) have DLR (which I had assumed were in the lower lamps but are a dimmed headlamp). In my lower lamps I have parking lights and another light with orange bulbs as indicators (turn signal). At the rear, the reversing lights have been converted the same way and an external reverse light mounted below the bumper (visible in avatar pic). Maybe something in all that lot.

Not sure how much I did before is valid as multi meter had blown fuses so think I'm starting from scratch again. PITA!

Battery drain - cause?

99Yak

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HotWheelsBurban

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Pinger

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Pinger

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HotWheelsBurban

Gotta have 4 doors..... Rawhide, TOTY 2023!

RawbDidIt

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HotWheelsBurban

Gotta have 4 doors..... Rawhide, TOTY 2023!

Pinger

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