Weird current draw

[Jobi-Wan Kenobi]

Has anyone ever experienced a parasitic draw that would alternate between .7 and 3.4 amps? I thought I was having connection issues with my meter, but even once I had solid connections the draw would still change. It seemed to change about every 20 seconds or so. I don't know if I'm dealing with one draw or more than one. I checked all of the ATC type fuses that were under the hood but so far no of those were it. I checked the alternator but that wasn't it either.

Still has the stock audio system. No other electronics added that I've found yet.

 

[Fless]

What are you driving? Make, model, year might help. Think about putting it in your signature so it's always there.

You're letting the truck go fully to sleep, and not opening any doors, etc.? 3+amps sounds about like what the interior lights would draw when on. Maybe have a flaky or dirty override button on the light switch?

If you have the AUTO HVAC head, those can take anywhere from 3 to 5 hours to fully go to sleep, but it should draw maybe 60 or 80 mA when awake (with the truck shut down).

 

[Jobi-Wan Kenobi]

@Fless its an 03 Tahoe LT (just added it). I never checked inside if the lights were on, but the time that I spent just pulling and probing fuses would have been enough for them to turn off after the battery being connected. And in that time the draw had jumped a couple times. But even just doing other things I never noticed the lights on. I just thought to check because last weekend the battery was completely dead when I turned the ignition on and when I checked voltage today it was going going dead again. And it does have the auto HVAC head.

 

[Doubeleive]

@Fless its an 03 Tahoe LT (just added it). I never checked inside if the lights were on, but the time that I spent just pulling and probing fuses would have been enough for them to turn off after the battery being connected. And in that time the draw had jumped a couple times. But even just doing other things I never noticed the lights on. I just thought to check because last weekend the battery was completely dead when I turned the ignition on and when I checked voltage today it was going going dead again. And it does have the auto HVAC head.

check the blower motor resistor, they have been known to fail and make the blower motor continue to run after the vehicle has been shut off, If it looks ***** at all I would just replace it. that would be my 1st suspect anyway, then if that is not it try unplugging the alternator, then maybe the instrument cluster. in that order.

 

[Fless]

If I read that correctly you're pulling fuses? A better way is to measure across the test points on the mini fuses to see if any current is flowing. That way you're not waking up modules when the fuses are reinserted. There's a chart for each fuse style to convert the voltage drop to an approximate current draw. There are links in a few other threads, but shout if you need need a link to the conversion tables. Lots of good parasitic draw videos on YouTube (South Main Auto for one).

 

[Jobi-Wan Kenobi]

@Fless I was probing the fuses with a test light to see which ones were hot then pulling the hot ones one at a time to see which one would cause a drop in the current reading on the meter. I had the meter connected in series on the negative side of the battery. But you're saying to just measure current across the fuse with out pulling it? I had never thought of doing it that way.

 

[Fless]

Technically you measure the voltage drop across the fuse test points, and use the chart to convert to mA. Here's the chart for Mini Fuses: https://m.roadkillcustoms.com/wp-content/technical-pdf/Mini Fuse Voltage Drop Chart.pdf Any fuse that has a voltage drop is carrying current.

Here's a video on testing:

Some common areas of draw on these trucks are 1) silver migration on the instrument cluster circuit board; 2) water intrusion into the PCM connectors (pull both and inspect for corrosion and pin fitment; and 3) the RAP staying on after opening the cabin door (usually caused by a dirty or defective door latch). I'm trying to remember if there are any others that are common.

Sometimes a thermal camera can help find a warm circuit/fuse/relay.

EDIT: there is a bundle of wires that runs under the driver's side threshold at the front door. Pop off that threshold, unwrap the wire bundle and inspect for wires rubbing. Check all the way forward to the firewall.

 

[Jobi-Wan Kenobi]

Thank you @Fless . I never knew there was info out there to equat drop over a fuse to current flow. Very good info.

I hadn't heard of silver migration yet in the instrument cluster. The gauges seem to be functioning properly but looks like would be a reason to have it rebuilt. What is the RAP?

 

[mattbta]

RAP = retained accessory power. when the power stays running to radio/lights/etc until a door opens after key off.

 

[Fless]

RAP = retained accessory power. when the power stays running to radio/lights/etc until a door opens after key off.

^^ This. Try this test: run the truck for a minute or so and leave the radio turned on. Turn off the engine, remove the key (the radio is still on), and open the driver's door. The radio should turn off when you open the door. If it doesn't, then the RAP is incorrectly staying on.