To anyone that can help:

I have an unidientified battery drain issue with our '02 Blazer. I've unplugged the underhood light, disconnected the negative cable and put a test light between the cable end and terminal on the battery. I then proceeded to pull every fuse in the underhood fuseblock as well as the end-of-dash fuseblock one by one and the light never went out. Next I pulled off the front passenger side tire and disconnected the wires from the starter one by one hoping for an indication of where the problem was. The only problem I found is that the light never went out. Has anybody had this same problem and if so where did you find the source of the drain? Any help or ideas would be appreciated.

 

If you are sure that you pulled ALL of the fuses AND CIRCUIT BREAKERS out, then the next step is to start unhooking the battery cable connections (like you did with the starter)....next I would pull the battery cable off of the stud on the alternator. Then the battery cable connections at the fuse block or a wiring junction block if it has one. But you should be doing this test with an ammeter, not a test light. There is always going to be SOME draw on the battery, the spec on this truck should be no more than 25 mA.(.025A), but even that small of a draw will still light a test light (very dim, but still lit).

 

Thanks for the tips, I'll check those other places as well. Just an FYI, I started the test using my mulitester but I found that the test light was easier to see from a distance. The drain is around 12V so I used the brightness of the light at that voltage as a reference when watching for it to either go out or dim considerably. Thanks again for the info.

 

A battery drain is not measured in volts, It should be measured in series with the loads and you are looking for Amps, not voltage. I can understand that a test lamp is easier to see, but it can be more of a problem than a help in this situation. The old cars had basically no drain on the battery when everything was powered off, so a test light worked fine for them, but the modern cars always have a small drain on the battery, so it will be inconclusive to test for a drain with a test light. I should have mentioned before that this truck has a very specific test procedure for a battery drain...it is equipped with a Body Control Module (BCM) which will stay "alive" for several minutes after the key is removed from the ignition cylinder, and the doors are closed. I actually have touse the Tech 2 and go in and manually power down the BCM to start the test. So, you should first start by hooking up the AMMETER then make sure the ign key is not in the car, close all of the doors and wait for at least 10 minutes before you take a measurement. That should give the BCM time to power down and you can get an accurate reading of the power drain. Keep in mind that any time you cause a large drain (opening a door, disconnecting the meter...etc.) it will wake the BCM up, and you will see a big draw and have to start the whole process over.

 

That's the kind of explanation I 've been waiting for! Even a lot of manuals are vague when it comes to explaining why you must do something a particular way. I like to know why I'm doing or not doing something as opposed to "That's just how you do it". I've been using the "My buddy's dad's a mechanic and he said to do it that way" method, obviously it hasn't worked.

 

If you follow those procedures it will at least make sure you aren't chasing a problem that doesn't exist. If you don't make sure the BCM goes to sleep,you won't get an accurate reading. Be sure to repost your results.

 

After a few months without any luck in finding the problem, I finally took it to an auto electric shop. The mechanic told me that the Transfer Case Control Module needed to be replaced. He said that the TCCM wasn't the cause of the problem but that it was the effect and the problem was further upstream from the TCCM and replacing it would help him narrow it down. I haven'treplacedit yet due to a lack of funds, but I did find that when the TCCM is disconnected from the wiring harness, the drain on the battery is less than when it is connected. Any ideas as to what could be drawing power from the battery? Thanks in advance for the help.

 

NM I started my own post, I realized I was hijacking this one, sorry!