battery dead, 3 amp parasitic drain

[dan77062]

My 2015 sedan 3.8L battery was completely dead after sitting for 3 days. Nothing was left on. Figuring I got plenty of life from that battery for 9 years, I bought a new one and, in the process of installing the new one, discovered that there is a parasitic drain of about 3 amps.

I proceeded to go through the wiring and fuse boxes. Removing the main cable from the positive terminal battery assembly causes the drain to go to zero. However, pulling the 200A main fuse in the engine compartment fuse box does not reduce the drain at all from 3 amps.

Switching the passenger compartment fuse box to "OFF" reduces the drain to about 1 amp. Then pulling out the trunk fuse box power cable reduces the drain to 0.25 amps. Since I'd expect around 0.15 amps of drain in a normal car, there is only about 0.1 amp of excessive drain with those fuse boxes cut out.

Conclusion: there is a small short that is back feeding the passenger and trunk fuse boxes. Does that make sense?

How to continue to investigate?

 

[NC356]

Just my limited experience:
I always thought I had large draws; turns out all those little ECU's take time before resting.
Maybe try: measure draw though either the positive or negative cable in the trunk.
Close all doors; consider turning auto things like HVAC and headlights fully off
Hook up you leads and run them out the trunk opening to your meter. Then push trunk closed as far as possible and wait for a few minutes to see if draw goes down. Mine did.
***(Be ready with physical key to reopen trunk if it latched.)

 

[joegr]

Like NC356 says, it can take up to thirty minutes for the car to fully sleep after the last time you open or close a door, press a switch, bring the smart key near, or disconnect/reconnect a battery cable. You may be chasing something that isn't really a problem.

 

[dan77062]

THANK YOU!
That was exactly right. I was nervous about keeping such a large draw active that I didn't leave it long enough. I was also reluctant to fully close the trunk and trust that the key would get me back in there. Tested it and saw that it worked.

With the trunk and hood open, the draw stayed right around 3 amps regardless of time.
With everything buttoned up, the draw dropped from 3 to around 2.5 after about 30 seconds.
After 1 minute, it dropped to about 1 amp
After 5 minutes it was down to around 100 mA

Opened the driver's side door-- immediately went up to 5 amps. Closed the door-- immediately dropped to 3 amps and then followed the schedule above.

 

[joegr]

Ideally, it should drop to 20 to 30 mA after long enough, but it sounds like you are good.