Seeking Advice on Parasitic Draw on 09 Envoy SLT 4.2 I-6


New Member
Hi Everyone,

I'm trying to help out my not really mechanically inclined Mom that lives 1,200 miles away with a frustrating Parasitic Draw issue with 2009 Envoy 4.2 I-6.

OEM options/accessories: Heated Seats, Sunroof, Rear HVAC vents, 6 disc changer, rear TVs and DVD player.

Aftermarket accessories: Remote Starter, Aftermarket Backup Camera.

Here's the run down of Electrical System Issues and Repairs she has done lately.

Aug 2018: Battery Replacement

Oct 2018: Battery Failed, got warranty replacement.

Fall 2019: Intermittent starting problems.

Nov 2019: Starting issues persisted, upgraded to larger CCA battery with better warranty.

Experienced occasional starting issues after truck sat for days at a time, frequent situation since she is retired, doesn't drive daily.

Feb 2020: Battery would not charge with 12v wall plug in battery charger. Replaced under warranty 3 months after purchase.

Took vehicle to mechanic who tested battery, alternator, and ground. Found Alternator was pushing 15v, replaced alternator with reman.

10 Days later: Starting issues continue, will not charge properly, road side assistance jumped battery. Replaced battery AGAIN because it failed testing at Walmart.

Present day: Situation has regressed to the point where the battery will start draining within hours of the car being shut off.

She started hooking up the battery to the charger when parked because it had a trickle charging/battery tender function and claimed that it was showing as low in as short of a time span as 2 or so hours.

I finally got to the point where I told her to flat out DISCONNECT the battery cables when she parked and to leave the cables off until she absolutely had to drive it someplace.

She had another short appointment with the mechanic who claims he tested both the under hood and rear fuse box and that they were both showing some signs of drain. It doesn't sound like he went fuse by fuse to test of Amp drops.

I've told her to go back AGAIN and have him check the Remote Starter and the Backup Camera wiring FIRST then start going thru fuses.

If he doesn't find a definitive source for discovers that it's something more involved like the rear HVAC actuator motor she claims she can hear turn on then I want her to bring it to a dealer and have them deal with it.

Still with me here? Good! Now for my questions!

Is the ECU advanced enough on these trucks that an OBDII Diagnostic Scan could actually show a fault code for an Electrical Issue? i.e. isolate it to something like the HVAC actuator motor?

2) If the ECU is that advanced could the dealer "shut off" a power draining accessory?

3) Are there any known Parasitic Draw issues with these trucks that should be looked into?

Any other advice is appreciated!


Well-Known Member
I do not think the ecu is advanced enough to show anything like this, pretty sure you have to go old school with a meter and measure. It actually sounds like your mom's car has a pretty significant drain so surprised a mechanic didn't find it. But then again, these things can be tricky. I posted this 9 years ago about a drain problem, think it still holds true. Onstar has been known to cause problems in vehicles. But at this age it might be anything, radio, ignition switch. An electrician with basic car knowledge might be helpful to her if she knows one, it's a matter of measuring amps (milliamps) and then umplugging circuits. At least he can narrow down the cause, and possibly fix it if it's a wiring problem. Keep us posted it will be interesting to hear what is the cause. If it were my vehicle I would probably start with isolating to major components, like fuse boxes and work from there.

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.


Silver Supporter
I would place my bet on one of the two additions, more than likely the automatic starter. They could have used cheap wire connector and/or not soldered the joints and they are now grounding out.

Here are a few videos to help with diagnosing a parasitic draw. The first one is pretty long but, very extensive. The second video is a cheap and easy way, that even skilled (supervised) child could accomplish.

I would watch the second one first. It's also pretty detailed and it's only 11 minutes long. He mentions a second multimeter, which I do not think is needed if, you are doing all of the testing in 30 minutes or less. Just keep going back and check the battery voltage to make sure it does not drop below 10 volts.



Well-Known Member
I can only speak of my experience with a parasitic drain. Couldn't figure it out, so I had to do the same thing: disconnected the battery cables while it was parked for a week, otherwise it would drain the battery. Do that enough and it will ruin the battery so that it fails testing.

Turned out that I had accidently jammed the plastic switch on the power seat. Since that circuit runs whether the key is in or not, it would drain the battery. The seat had reached the end of the track, so it did not move, but the circuit was still closed because the switch was jammed on, hence the slow drain.

I would go with the multimeter method as in the videos - you can narrow down the drain to a particular circuit.


Well-Known Member
Open your glovebox and immediately check the bulb to see if it's hot.

How long after the remote start and/or backup camera was installed did this happen?

One thing to check is the hot lead for the backup camera. This could have been wired to the constant hot instead of the switched hot for the stereo.


My bet is one of the two aftermarket addons. Moreso the remote start as those tend to cause troubles.

Online statistics

Members online
Guests online
Total visitors

Members online

Forum statistics

Unanswered questions
Answered questions
Latest member
Top Bottom