Rear de mister

O

ori

Senior member
Can someone check if their rear de mister works like mine does?

If I get into the car, start it and push the button I hear it click on. If I stay stationary, it will stay on, but if I start driving it clicks off. Then back on again a bit later. On off etc….mostly off! Takes ages for rear screen to clear.
 
Can't say I've noticed it operating like that but will check tomorrow.
 
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Just had a quick 3 mile trip out. Rear demister came on and stayed on the whole journey.
I'll be using the car later this evening so will try it again.

Could it be the battery is on the way out and some safety system has kicked in due to insufficient voltage??
 
Just found this online:
  • If the demister consistently turns off prematurely or doesn't stay on for the expected duration, the issue is likely electrical.
    • Low or Failing Battery: BMW vehicles are "smart" cars that prioritize essential systems. When the battery charge is low or the battery is nearing the end of its life, the car may shut off "non-essential" services, such as the power-intensive rear demister, to preserve power.
      • Solution: Check the battery health. If the battery is old (typically over 3-5 years) or you notice other electrical issues (e.g., dimming lights, slow start), it may need to be replaced and coded to the car.
      • Faulty Switch or Relay: A problem with the demister button itself or the associated power relay can cause the system to cut out.
      • Wiring/Ground Issues: Damaged wiring, poor ground connections, or corroded plugs (especially in modules located near the rear window) can cause a voltage drop, leading to the system shutting down or failing to operate effectively.
        • Solution: Inspect all visible wiring and ground connections for corrosion or damage. Specific areas like the rubber grommet tube between the car body and the tailgate are common spots for wire issues.
      • Check Battery Health: This is the most common reason for BMWs to disable the demister.
      • Use an OBD Scanner: A diagnostic scanner can check for fault codes in the car's system that can provide more information on a specific malfunction.
      • Eco Pro Mode: Some BMWs may limit electrical consumption if the car is in Eco Pro driving mode.
        • Fix: Switch to Comfort or Sport mode to see if the demister remains active.
 
Thanks guys. Car is under 2 years old so don’t think it’s that. I’ll get it booked in with BMW.
 
Just as an update people.
Took my car in and in usual BMW stealer said no issue. So I had to go back and show them the problem. Guess what…..there is a problem. All they previously did was just plug it and checked for an error….which wasn’t there and that was the extent of diagnostics. Tech suspects a module might have a voltage error.
Car booked back in for Thursday.
 
As an update. Car went into BMW today and has been diagnosed with a faulty LIN module.
I have no idea what this thing does, but apparently it’s having issues and a replacement has been ordered under warranty. Will confirm after installed if this fixed the problem.
 
Further update.

Lin module was finally replaced and didn’t fix the issue. Some power thing was replaced and still didn’t fix issue.
BMW haven’t got a clue what to do next and apparently neither do bmw tech Germany.

I always wonder what happens if the can’t fix the car?
 
Another update…..

BMW technical seem to think it’s a battery issue. They had the dealership check for battery drain and they found none….however, the car battery which was on 100%, has dropped to 50% in a 2 day period so they suspect that the battery is faulty.

Honestly….this could be the case as these cars are super sensitive to battery issues.

New battery ordered….lets see
 
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Another update…..it’s not the battery. ;)
Car is staying with them and they are now checking all the wiring……..this should be fun.
 
ori said:
Another update…..it’s not the battery. ;)
Car is staying with them and they are now checking all the wiring……..this should be fun.
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They'll change the tyres next. Just in case it's that. :rolleyes:
 
Another update.

BMW tech Germany have asked dealership to change the body control module? If that is because of tests they have done or speculative is beyond me, but part will arrive Thursday and I guess we will know Friday!
 
Another update. Module has been changed and once again it is still having the same issue. Back to bmw Germany tech support for next steps.
 
I had the same problem and it turned out to be the relay. My car is a 2003 Z$ E85. The relay is accessible from behind the fuse box. Slightly awkward position, but once you locate it, it simply plugs in. I'd disconnect the battery as a precaution. The part number from BMW is: 61 31 6 919 113. £28 from Sytner Stevenage earlier this year.
 
@ori, It really seems like it's a guessing game doesn't it, on the bright side, at least it's summer and you don't need the rear demister
 
sars said:
@ori, It really seems like it's a guessing game doesn't it, on the bright side, at least it's summer and you don't need the rear demister
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You are correct on every count.

Only problem is, that while they are back and forth with bmw Germany trying to figure out what to do, my car is not put back together and I’m in an IX1.
The only positive is that with petrol prices where they are, I’m enjoying cheap motoring. Would rather have my car though! :(
 
Sean White said:
I had the same problem and it turned out to be the relay. My car is a 2003 Z$ E85. The relay is accessible from behind the fuse box. Slightly awkward position, but once you locate it, it simply plugs in. I'd disconnect the battery as a precaution. The part number from BMW is: 61 31 6 919 113. £28 from Sytner Stevenage earlier this year.
Click to expand...
Totally different car I'm afraid.
 
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