My Rear Window Defroster Does Not Work on My Convertible Back Window, Z4

Quote:

Originally Posted by Em/1

I don't think it is that stupid. I'll stick my neck out and point out that I just replaced my battery in 2004 Jag XJ8 at 100,000 only because it made me nervous. I'm getting same kind of readings as the OP when in accessory mode even right after a 50 mile mostly highway 40 minute ride and I think from what I have seen in other sources (Roundel) that BMW should be doing a better job with the electronics.

It does in that they are apples and oranges in many ways.

manufacturer, engine size, alternator size, battery size, and most importantly, the # of parasitic devices. don't know about you.. but most 1988 Hondas didn't have NAV systems, 12 speaker stereo systems with integral subwoofers under the seats, a hard drive, comfort access, bluetooth, and that's assuming the 80s vehicle has halfway modern creature comforts like heated seated seats and multiple defrosters for windows and mirrors. An 88 BMW had some items like those.. but not an 88 Honda.

It's absolutely ridiculous to compare the power requirements between vehicles made 20 years apart, as if 20 years of technology didn't occur.

Ever sit in your newer BMW for a few minutes after you turn the engine off?

Did you know that Bluetooth is still on? I have had my car take a call for me when it is in the garage and I was in my home!
Did you know that your iPhone can still be charging via USB?
Did you know that the stereo will play for 20 minutes before it turns off?
Did you know that the ignition circuitry is still energized including the push button remaining lit?
Did you know that the Angel Eyes remain ON until the driver's side door is opened?

How about comfort access... this system certainly is going to draw some current waiting for the owner to return. The OP has even mentioned that " touch access" doesn't work when he returns. That's because the only way this system can work is that a low power radio is on waiting for the owner to turn on so that it can wake up the car, and unlock the doors, and flash the lights, turn on the angel eyes and the rear taillights, and happily chirp a Hello beep.. (wow... that's a lot of power draw before the door even opened and the interior light came on! right? )

Ever notice once you get out and close the door..? hang around for about 3-5 minutes and listen to the whirring that goes on several minutes after the vehicle goes off.. and wait and see how long it takes for the push to start button to go out.

Using some of these features for even a short period of time with the engine off will have a serious effect on an already weak battery, and the great likelihood is that many of them are likely in use, along with many others. With multiple amplifiers and subwoofers, even playing the stereo at moderate volume for a few minutes after shutoff will eat into the reserve of your battery.

Quote:

Originally Posted by mccand

umm... whats the battery cable recall?
Also, any word on an "accessory" mode for radio on while car off?

Quote:

Originally Posted by EldRick

A) "umm... whats the battery cable recall?"
Ask your dealer.

B) RTFM. "Radio" mode does not activate all the high-drain secondary stuff, like climate control and set-heaters. Push the start button Once, without using the clutch pedal.

I'll see your RTFM and raise you one. Here is how I get in and turn on the "radio " mode.

1- Open door.
2- Push radio knob button to turn radio on. HEY LOOK MA! I didn't even hit the Start button!

OP. As an an FYI. When a vehicle battery is low...

a number of bad things can happen...

1- you may see any number of odd or random errors.. or odd lights on the dash... Defrost...airbag system lights.. check lights.. seat belt system etc.. basically ANY system circuit can show an error
2- vehicle headlights may dim or go out
3- vehicle subwoofers will not operate
4- vehicle radio will not operate
5- you can deplete and eventually kill your battery
6- you can damage your vehicle charging system (alternator, diodes, voltage regulators, starter, ecus, )
7- the vehicle may not idle properly and will stumble and eventually die at idle
8- you could blow up your motor.

What if the item getting a weak/intermittent/wacky brownout sort of power is the ENGINE ECU. If the vehicle brain can't think clearly... then it's not going to meter air/fuel ratios properly or even react to knock sensors) . Go out hot rodding with a worn down charging system, and the motor could go KABOOM.

Any, of the above items can occur on a vehicle that has a battery that still can have enough charge to turn over and start the vehicle. So. to answer your original question... could the multiple electrical issues you are having (no comfort access... no rear defroster... and.. rear defroster working at the end of a long drive) be the result of a weak battery? YES.

My Rear Window Defroster Does Not Work on My Convertible Back Window, Z4

Source: https://www.1addicts.com/forums/showthread.php?t=1078691

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