[Processing61]

Hi,

Getting round to sorting some problems. My rear heated windscreen has never worked. BMW E91 touring msport auto 2008. Checked the easy things first, fuses and relays related to the heated windscreen and they are all good. It’s done quite a lot of miles so with the boot opening and closing I was thinking the wires through the channels near the hinge on the boot could be broken, so I’ll check there next. I had some issues like that on an E90.

I was curious to know if there were any common culprits for this problem?

TIA!

[POBEP]

Originally Posted by Processing61

Hi,

Getting round to sorting some problems. My rear heated windscreen has never worked. BMW E91 touring msport auto 2008. Checked the easy things first, fuses and relays related to the heated windscreen and they are all good. It’s done quite a lot of miles so with the boot opening and closing I was thinking the wires through the channels near the hinge on the boot could be broken, so I’ll check there next. I had some issues like that on an E90.

I was curious to know if there were any common culprits for this problem?

TIA!

I had this problem few years back.
In my case, it never worked in the morning (when I needed it most).

For a few years, I blamed shop that did minor work and potentially screwed up wiring when replacing headliner.

Then it suddenly start working every time. I could not find an explanation.

Finally, I realized that the functionality was restored after I replaced dying 10 year old battery.

Turns out if you have weak or discharged battery, the rear window heat will not work as car tries to "save" the remaining charge.

[Arch Stanton]

Def try a battery change if it isn't young, heat is a big draw on energy and the rear screen heater is one of the first things to be sacrificed when there is a big demand on an old battery.

[Processing61]

It seems to be measuring ok voltage wise when the engine is off and when on. But it is a BMW Exide battery so could well be the original. I don't suppose it would show a manufacture date somewhere? I can't seem to find it.

[POBEP]

Originally Posted by Processing61

It seems to be measuring ok voltage wise when the engine is off and when on. But it is a BMW Exide battery so could well be the original. I don't suppose it would show a manufacture date somewhere? I can't seem to find it.

What is the voltage:
1. switch off engine
2. turn on headlights
3. wait 3-5 minutes
4. record value

[pmorg4]

Originally Posted by Processing61

It seems to be measuring ok voltage wise when the engine is off and when on. But it is a BMW Exide battery so could well be the original. I don't suppose it would show a manufacture date somewhere? I can't seem to find it.

The date on original BMW batteries is often stamped on the top of one of the terminals.

[Processing61]

Originally Posted by POBEP

What is the voltage:
1. switch off engine
2. turn on headlights
3. wait 3-5 minutes
4. record value

Will check this, thanks!

[Processing61]

Originally Posted by pmorg4

The date on original BMW batteries is often stamped on the top of one of the terminals.

Totally missed that. Luckily I took some pictures and could just see it. 2008 so it is the og battery. Thanks!

[pmorg4]

It's done very well to last this long! I think a replacement would be a good idea if there's any concern over its ability to hold charge.

[Processing61]

Bit of an update;

Replaced the battery, went with the Yuasa YBX5019 from Tayna Batteries.

Still have the fault with the rear windscreen not heating/de-misting/de-fogging, so I will be looking into this further soon. The battery needed to be changed anyway so that’s ok.

I’ll update with any further findings

[F31B48]

Originally Posted by Processing61

Bit of an update;

Replaced the battery, went with the Yuasa YBX5019 from Tayna Batteries.

Still have the fault with the rear windscreen not heating/de-misting/de-fogging, so I will be looking into this further soon. The battery needed to be changed anyway so that’s ok.

I’ll update with any further findings

Did you register the new battery to the car? Registering the battery also resets the power management function in the DME/DDE which is what disables the heated window etc. It won't start working again unless it's reset. I've copied some info below from ISTA.

Notice! Register battery replacement

After installing a new battery, the service function 'Register battery replacement' should be run. The battery replacement has to be registered in order to tell the power management system that a new battery has been installed in the vehicle. If the battery replacement is not registered, the power management will not function properly, with the result that Check Control messages may be displayed and functions limited by individual electrical consumers being switched off or having their power consumption reduced, for example.

[F31B48]

Also noticed that your old battery is an AGM battery but the new Yuasa one you installed appears to be a normal lead acid. You will need to get it coded to the car, so it knows it has a normal lead acid battery.

[Processing61]

Originally Posted by EvaBmw

Also noticed that your old battery is an AGM battery but the new Yuasa one you installed appears to be a normal lead acid. You will need to get it coded to the car, so it knows it has a normal lead acid battery.

Yes I was surprised about that. I ordered the Yuasa without even thinking it could be AGM, as I thought from the factory only start/stop cars were fitted with AGM. It wasn’t until I lifted the battery and thought “hmm, I can’t hear any liquid moving”, then looked at the codes and realised it was AGM and I had already bought the battery. I am ok with sticking with the Yuasa lead acid.

And yes, battery is coded and registered. I believe I used INPA to register the new battery change and NCS to code the change.

Thanks!

[Willygbr66]

I had the same issue. It turned out to be one of the resistors had shorted which is located in one of the rear pillars.

I have an E92. Bit of a pain as you have to take a few interior panels off to access. Plus side is the resistor is the same as in mini’s and I pick one up at a local breakers for £10.

[Processing61]

Originally Posted by Willygbr66

I had the same issue. It turned out to be one of the resistors had shorted which is located in one of the rear pillars.

I have an E92. Bit of a pain as you have to take a few interior panels off to access. Plus side is the resistor is the same as in mini’s and I pick one up at a local breakers for £10.

Thanks, I'll have to check this out! This is next on the list

[ptpending]

e91 has it's own problem
the wiring in rubber tubes from door to windscreen
and wiring from body to rear door