Whenever I am going to be testing for a battery drain I want to know the condition of the battery. This battery had been on the car less than a month but tested bad. I needed a good battery on the car while testing so installed one from my own stock. I forgot something very important. New does not mean good. We'll come back to that.
With a new battery on the car I did charging system tests and battery draw tests. The battery draw would be where any excessive battery drain would show up. Battery draw was fine at this time so I was probably looking at an intermittent problem. There was the possibility as well that the original battery was bad but so was the replacement. Not likely, but possible. I told the customer I should keep the car overnight and see if anything showed up as a drain. That being settled I moved to checking the cooling fan. The fan was working at this time. So far, I was getting zero co-operation from this car! I have seen a lot of problems with intermittent cooling fan operation on these though. The system is usually fine after replacing the fan module assembly. Rather than wait for the fan problem to appear at a bad time it was decided to replace the fan module and recharge the a/c.
No battery drain happened overnight, the car cranked fine, the a/c worked great and the cooling fan was fine. We put the bad battery in the trunk and left my new battery in place on the car. I parked the car outside and about an hour later the customer comes to pick it up. It wouldn't crank. The battery was completely dead. I was completely at a loss for words! After stuttering and sputtering and head scratching a bit I just started testing from the beginning. Remember "new does not mean good"? When I tested my new battery it was bad. I don't mean discharged, I mean bad as in not good. I pulled another new battery but tested this time. Testing good, I installed yet another new battery. I told the customer to let me know of any problems. I was still pretty sure the car had an intermittent drain but after this unforeseen battery fail fiasco I was off my game just a bit. He had no other ride and no time to wait for another battery draw test.
Let us now move forward. The car was fine for several days before once again draining the battery overnight. It was arranged to leave the car for at least a couple days if needed. Once the car was dropped off I parked it inside the shop to get it prepped for tests. First, test the battery. My preferred tester works best if I connect it directly to the posts with the car's wiring completely out of the picture. Especially when I could have a problem with excessive draw. I have a "memory saver" unit that connects to the car diagnostic connector and provides power to the car electrical system while I have the battery disconnected. This preserves memory and prevents a sudden power loss that could affect any cause of excessive drain that might be present.
Battery was good, slightly under a full charge but good. I reconnected the battery, put the memory saver away and tested the charging system.
Good battery and good charging. I shut everything off and figured I would put the charger on to top off that battery while I was waiting for the cars computers to go to sleep. After that I could test draw. Now I had noticed the 96% capacity on the battery test results but the charger showed 90%.
This bothered me a bit. It made me keep a closer watch on the charging progression. After about a half hour the 90% was still 90% and that was odd. I decided to test the battery draw. Depending on the system if you check draw while a computer is still active you expect 100 to 400 mA. If the system is asleep you are looking for about 50 mA, again depending on the system.
Wow! Something was on and it was more than a computer not sleeping. It was by now shop closing time but if I didn't find this now it might not be there in the morning or the battery would be down and I'd have to start all over. Or both. I decided to find this problem while it had decided to give me a chance. The next step was to find which circuit had the draw. For that you begin pulling fuses and watching the meter. I started with the underhood fuse block and the smaller mini fuses. These fuses will usually have fewer things on the circuit that they power. Once you find which fused circuit the problem is on you have to trace further to isolate the component of that circuit causing the drain.
Decide where to start when pulling the fuses and follow a pattern. It also helps to take a "before" picture as a guide later just in case you get confused as to where the fuses go back. Have a place to lay each fuse as it comes out. I try to re-create the same pattern as was in the box. As you pull each fuse you'll want to watch for the meter reading to drop. If you pull a fuse and there is no drop don't put the fuse back. Putting the fuse back could trigger another system to kick on and now you aren't looking at the same draw. I started with that green fuse at the top right and went down that row.
Not much was happening until I pulled that last blue 15 amp fuse next to the bottom of the row. Then the meter showed I had found the circuit with a problem. Something that fuse powers was causing the battery drain.
Before going further on though it is best to close up the other circuits. To me, it makes things less likely to lead to false conclusions if I keep the system as intact as possible. I put back all the fuses except for the one with the problem. If you put a fuse back at this point and it does wake up a system, you wait for the timeout and go on with your diagnostics of the problem. In this case though no other draw appeared and I was only with one fuse out of the block.
Now it was time to find out more about this fuse and what was on it. I just stuck the fuse into the block once again and noticed that besides the draw jumping back up on the meter that I heard the a/c clutch on the compressor kick on. I distinctly heard the click. While that did seem like a big clue it could also be a false lead. There might be a software program in place that has the computer cycle the clutch once anytime that circuit powers up. You have to find out just what fuse this is. The fuses are numbered and the schematic is on the fuse block cover. According to the cover I was looking at fuse 11.
A quick check of the wiring schematic for fuse 11 shows it to power (surprise!) the a/c clutch relay.
I put the fuse 11 back into the box and pulled the a/c clutch relay out instead. The draw was gone. The relay was powering the a/c clutch even after the car was off and sitting parked. That was the battery drain. The relay was stuck or something in the wiring was closing the relay. It seemed like it would be a simple check to take one of the other relays (same part #) and place it in where the a/c relay was before. I did that and there was no draw. I put the original a/c relay back in and the draw came back, clutch kicked on. The a/c relay was stuck on.
I replaced the a/c clutch relay this morning and patted myself on the back a few times. I have to say the car was much more co-operative the second time 'round. Just a few more pictures, bear with me. I wanted you to see what is a typical key off battery draw on this car with the computers still awake. (after the fix)
After the computers go to sleep.
If you know me, you won't be surprised that I just had to take that relay apart. I was amazed at the picture I could get with the iPAD. You can see the contacts that were burned and sticking.
As always, hope this helps you.
Kenneth Hayes
G&G Auto Repair
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