Hi, I new here, I have a 99 c5 we purchased in February this year. Ever since we have had it it won't stay charged , so I checked the battery wasn't holding a charge. replaced with a new optima battery 2 months ago . We don't drive it very much, but even with the new battery it drains it totally. I put battery on charger, fully charged then put back in car. After a week it started but the next week its dead again, Now I know you have to drive the car to keep it charged but it shouldn't do that with a new battery. I have cleaned a couple of contacts but i was going to do a through cleaning of the connections today, well the ones i can access easily for now. But I am thinking something is shorting out beings its been going on all year. I have read the forum on electrical very helpful if anyone has ideas I would love the advice. I am just trying to see if its something I can fix before I have to take to shop. Thank you in advance.

 

Welcome to the Forum !!…the more your new battery becomes discharged its life will be shortened considerably…best bet is to take it to a shop not knowing your electrical skills…it can be a few things so a shop should be able to handle this !!

 

97-99 Corvettes are known to have a battery drain from the Electric seat adjuster on the driver's side
Try un plugging the pigtails ( more than 1 I think ) under the seat

 

Some good videos to watch: https://www.youtube.com/results?sear...+battery+drain
If you watch a couple of those and think it's something you can try post back with some specific questions about what you need help with.

 

You may be able to fix it yourself, if you are proficient with a DMM, we will be able to help you if you are.

 

Welcome to the forum. Here are a few posts I've copied regarding your issue. C5 battery drain. Checking current draw.
For those of you who have C5's that have problems keeping the battery from going dead if you leave your car idle for a short period of time, here is a procedure that you can use to see if your car is drawing an excessive amount of battery current. The C5 corvette should be able to sit idle for weeks without running down the battery far enough that it will not start.

If your car has a good battery and it depletes the battery in a few days or a week, use a DC Amp meter to measure the battery current draw when the car has entered the BCM sleep mode.

Once ALL of the cars loads are removed (i.e. doors shut, trunk shut, interior light off, radar detector and phone chargers removed etc, (make sure that you disconnect the under hood light), disconnect the battery NEGATIVE terminal. Connect a DC AMP METER capable of reading at least 10 amps in SERIES with the NEGATIVE battery terminal and the NEGATIVE battery cable. Once you connect the amp meter into the circuit, the car should power up and enter the "SLEEP MODE" within a few minutes. It should not take longer than 10-15 minutes. If the car is in the RAP (retained accessory power) mode, it may take that entire 10-15 min to power down.



Battery drain test with more detail




The battery cables MUST be properly torqued to the battery with a torque wrench to 11 FT/LBs. If you can ever move the terminals by moving the battery cables, the terminals are NOT tightened properly.

Remove them, clean them and re-torque them on the battery.

BC







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When you initially connect the AMP meter in the circuit, the current draw will be high. Somewhere around 8 amps. As the BCM determines that the car is secure, it will start dropping off loads and go into the SECURITY MODE and Sleep Mode. As it drops off loads you will see the battery current drop down from 8 amps to around 2-3 amps them in the milliamp range.

If there is a unwanted load, it could take up to 10-15 min for the current reading to settle out as low as it will go. The target reading will be 15-20 milliamperes. As you can see in the next photo, my 02 ZO6 draws .02 or 20 milliamperes.



With this small current draw and a properly charged battery in good condition, your C5 should be able to sit idle (without a battery tender or battery charger) for at least 3 weeks if not longer. My ZO6 has set idle for 30 days and started normally after that period.

C5's that drain batteries in days or a week have an excessive battery current draw issue. Here are a few places that have proven to be a cause of excessive battery current draw:

1 Drivers or Passengers seat control multifunction switch. The return spring in the switch gets weak or damaged and the seat sticks in a movement position. The motors are thermally protected by a "circuit breaker" in the passenger’s foot well and will continuously set and trip until the battery goes dead.

2 Driver’s LUMBAR motor. Same as above!

3 Interior lights, dash lights, or other interior lights.

4 Head light motor control module. The module can short inside and draw current even though the lights are down and secure. If you feel the module and it’s HOT, it’s bad.

5 Alternator. The diodes can and do go bad. If they go bad, the field windings will always be powered and draw current. If you suspect that the alternator is drawing current, remove the field terminal wire from the back of the alternator and insert the AMP Meter in SERIES with the circuit (between the red wire and alternator field terminal). The current draw should be ZERO. If you have current draw, one or more diodes are bad in the alternator. The last alternator that I checked this way was drawing 5 amps.

6 Bose Amplifier. There’s an amp under the dash on the driver’s side dash. The relay for that amp sometimes sticks and the amp remains on even though the car is OFF.

Cell phones, radar detectors, wide band controllers etc... can get left plugged in.

NOTE! If you open the door, or trunk or even remove and then replace a fuse for troubleshooting, it will wake the car up and you will need to wait for it to enter the SLEEP mode again to read the current draw.

If you remove a BCM fuse, it will negate the test because the BCM is controlling the current draw.

Hope this helps figure out the reasons for premature battery failure.

Bill Curlee

Did you pull the codes BEFORE you removed the EBCM??? What were they??????

What have you checked to try and find the cause of the battery drain???? There are many common causes....


Here is a portion of a post by Bill Curlee, the Forums resident electrical wizard:

The correct BCM current draw should be 30 Milliamps or less. Most C5 run around 25ma
but I have see some as low as 15 ma.

Leave the engine compartment fuse box for last and start with the passengers compartment
box first. Pull the power seat breakers FIRST! The power seats have a tendency stay on
and cause this issue.

Also pull the fuses for the Bose system amp.

Examine the car in the dark for lights staying ON.

Once you prove the interior circuits good,,, check the headlight circuits, and then test
the current draw of the alternator.

Look at my electrical stickey. I think I cover this in detail in that post.

There are several COMMON things that cause excessive current draw

-Seat multifunction switch & Lumbar Switch
- Bose Amp relay stuck on
- Alternator didoes bad and drawing current
- Headlight control module bad
- Interior light on (check in the dark)
- Added aftermarket accessory not shutting off







And here is Bill's thread on how to further narrow down a current drain:

http://forums.corvetteforum.com/1567522286-post590.html









One common problem with unknown battery drainage is; the drivers seat adjustment switch. I had this problem too so as test I unbolted the seat to get access to the bottom and disconnected the harness.
That solved my problem. Be sure to adjust the seat to your liking before you do this



I want to thank everyone for their help ...Found out the battery had a bad cell...changed it out and I did the test as suggested, (The tender is still good battery couldn't hold a charge). After checking the system and then waiting 20 min and checking it again the car was shut down no draw. I didn't realize the 02 had a sleep mode, feel like a bonehead. but the Vette started right up very strong this morning. No hesitation or slow cranking. Thanks again for all your suggestions and advise. Bill



The best way to perform a parasitic draw test.

 

Just a reality check. My 04 Z06 has 41k on it and recent battery change. Takes about 3-4 weeks and when starting.. it starts but you can tell it turns over slower than it ought too. So if I go longer than 2 weeks I'll plug my battery tender in. Generally takes about 48hrs for the battery tender light to turn green.
With the previous battery that came in the car (who knows how it was stored) it wouldn't start in only about 2 weeks time.

 

Welcome to the forum! It's great you figured out the battery was the culprit. C5s seem to eat more batteries than kids eat candy!! In my case, the Body Control Module had failed. A lot more $$ than a battery!!

 

Good advice given in the above posts regarding locating the source of your battery drain. The first time it happened with my 04 shortly after purchasing (used), the battery was 7 years old. Naturally I figured the battery was bad, replaced it with a new one, and the next morning it was dead as well. I fought the problem for a week or so until I happened to have my hand beneath the interior mirror and noticed the map light shining on my hand. I figured for sure these things would be on the electrical circuit that times out and cuts power, but apparently not.

Pushed the switch off, and cured the problem . . . . . evidently I had inadvertently pushed it on at some point, had no idea the car even had map lights . . . . .

 

I keep mine on a charger, if not, and no driving for 2 weeks, it gets weak. The 12VDC receptacle is constant on, so don't leave things plugged in and on.

 

I'll give you another one, and I've never heard of this one before: The glovebox light staying on with the door latched! Yup, happened to me, and the only way I found it was my 12 year son. Reason he found it is he was obviously shorter than an adult, and his eye level was closer to the gap between the door and box. He dropped something, bent over to pick it up, and says 'Hey dad, what's that light in the dash for?' I said there wasn't one. He said 'yes there is, it's behind this door.' He was right!! For some reason, my door wasn't pushing the switch plunger in far enough to kill the light. I ended up sticking a thin (maybe 1/16"?) round piece of black plastic on the door, to hit the plunger sooner. That was over 15 years ago, and still working. Hope this helps someone.......

 

Glove box and trunk lights have been a problem over the years running down batteries when they should have been off, but the timeout circuits feeding many of these items on later model cars cured many of these problems. Under hood lights were sometimes a problem as well, but to a lesser degree. I had the same glove box light thing occur on my wife's Continental she owned a few years back, she could see the glovebox light on from the passenger's seat, but I couldn't from the driver's seat. I thought she was seeing things since it had apparently been doing it for some time, but never any problems with running the battery down. So, I purposely left it on one night to see, and the next morning it was off. That's when I figured out it would time out along with other electrical item, never any problem.

I wrongly assumed the 2004 LeMans Corvette would time out the map lights as well, but after I found that it wouldn't!!

 

Found a cool little trick as to how to NOT disconnect the battery

 

I have been studying posts on this forum and using them to diagnose my battery draw issue.
First of all, thanks for very thorough and easy-to-follow instructions, especially Bill Curlee.
This 98 C5 had a dead battery after 4 days, so I started measuring and removing the fuses.

I measured 1 A current draw right after connecting the circuit.
After ~15 min it dropped to 0.34 A. So this is ¨10x the permissible amount.
I started by disconnecting all vanity stuff, like radio (aftermarket), seats, door control modules and such. After a while I had ALL fuses taken off (including PCM and ABS!) except:
-13 BCM I1
-22 BCM I3
-23 BCM 2
-25 BCM & IPC
These above were the only ones connected and still 0.35 A amperage was shown on my multimeter.
I disconnected Batt+ terminal and the small connector from alternator. No change in current draw. I disconnected both seat connectors also with no change.

Then I started disconnecting BCM fuses in the order I listed above. When I got to 25 (BCM & IPC) the current dropped to zero (it fluctuated between zero and something).
So I guess I can't bypass BCM and IPC

Is there any further tips to investigate this, does this mean either my IPC or BCM is bad?

 

Damn I feel stupid... After all these measurements I checked the dimmer button which was turned all the way clockwise. So the interior lamps were on. I also noticed that there were no bulbs in the rear view mirror so that's why I didn't realize this.
Now the current draw is 0.05 A when the car is at sleep

 

I went thru this on my Dmax truck recently. A couple of points that may help.

1. Most modern plastic blade type fuses have 2 little contacts where a volt meter can be connected. You can measure across the 2 points if you have a sensitive enough meter. The fuse has some resistance so current flow will cause a voltage drop across the fuse. Different value fuses will have different resistances, so you need a chart for each type fuse. The advantage is that you don't need to break the circuit to measure current flow which speeds up troubleshooting and prevents "waking-up" something that was asleep.

2. A large percentage of the time, excessive parasitic draw is due to aftermarket items either drawing current directly or causing computer/s to not go to sleep. So first thing to do is disconnect/remove all aftermarket items.

In my case with the truck, prev owner had wired in a relay that powered aftermarket backup lights. It tapped into the cargo light (bed light) switch. What I learned was that the cargo light switch does not directly power the light. Instead it sends a signal to one of the body computers to turn ON the light. It does this by using a 12V pull-up circuit. When the cargo light switch was activated, it simply grounds the 12V pull-up line. The computer sees the voltage drop and knows the switch has been turned ON. The relay added by the prev owner would get ~12V when the switch was off and ~0V when switch was ON, which is backwards but the relay had an extra set of contacts that would be connected together when there was ~0V. This is how it was wired. This arrangement would intermittently cause the truck body computer to not go to sleep. Only took me a year (and a set of batteries) to figure it all out.

 

Background:

All modern cars have a quiescent current draw from the battery. In other words, if some systems were not powered up at all times, the car would never "hear" your remote control and know when to unlock the car. The commonly accepted maximum quiescent draw is fifty milliamps. At this rate of current draw a suitably sized battery, in good condition, should last a minimum of +/- three weeks and still be able to start the engine. If you don't intend to drive the car at least once every three weeks, the battery should be connected to a maintainer, NOT a trickle charger.

Starting the engine once a week and allowing it to idle for ten minutes will cause excessive mechanical wear to the engine and may not keep your battery sufficiently charged. Use a maintainer. The Battery Tender, CTEK and no doubt other brands offer suitable solutions. Use them.

 

Yup,that dimmer switch killed my battery 2 times so i dont ever touch it again,lol