OBC swap from 535i to 525i Touring?

[pundit]

I'm am attempting to swap the OBC from my E34 535i (Nov 1989) into my 525i Touring (April 1992).

There are two part numbers on the rear of the OBC...

65.81-1389619 - BMW
65 91 11.19.11 - SIEMENS

The Touring is fitted with the digital clock/date/memo/temp unit (not the basic analog clock) and also has the full Check Control instrument cluster display. The 525i's plug and loom appears to have the same compliment of connector wires as the 535i.

Today I removed the OBC from the 535i and connected it to the plug in the 525i Touring but got nothing. No display (not even 'PPP'), lights or anything! It seemed completely dead.
I tried it again back in the 535i just to make certain it was still working and it was fine.

I've yet to fit the indicator stalk with the OBC cycling switch from the 535i (though I believe I may require an airbag compatible version)

QUESTIONS

Do I also have to fit the 535i's indicator stalk in order for the OBC to work at all?
(I do intend to fit it anyway but I wanted to make sure the OBC was going to function in the 525i first)
Do I need a coding plug?


Thanks

[pundit]

Hmmm it appears it maybe a grounding issue.
I didn't actually fit the OBC into the center dash.
I just connected the plug.
There is a metallic strip on top of the OBC that appears to be a ground.
I'll try it again tomorrow!

[myles]

depending on the options that your 535 had you will either need to fit the obc horn relay under the rear seat(at least thats where it belongs on the sedan) or if your 535 had the dwa alarm you need to fit it instead (both options plug into the same green plugs under the rear seat). It supplies power to the obc on one circuit that the clock/temp unit doesn't need.

I've done the same retrofit to a 94 525 and this was necessary.

[pundit]

Thanks Myles.
Now I have to locate the relay position under the rear seat.
Plenty of discussion about it on the net it seems... but no pictures!

[myles]

its infront of the general and relay modules and screws onto the inside of the kick panel behind the rear left passengers feet.

[pundit]

its infront of the general and relay modules and screws onto the inside of the kick panel behind the rear left passengers feet.

Thanks, I eventually managed to find a vague picture of it.

http://www.bmwland.ru/faq/obc34/obcrele.jpg

It doesn't look like a standard relay.
It's more like a rectangular module with its' own fuse.

Under the rear seat of my 525i Touring I found a connector with four colour coded wires that matched the colours of the aux horn relay module connector in my Bentley manual circuit diagram. What had me confused was the connector itself didn't match the terminals of a standard relay. The plug had four round female terminals. I assume this plugs into the aux horn relay module?
The catch is finding one of these. Do you know if E32's use the same relay module?

[pundit]

Here's some better pics of the relay module removed
http://www.bmwland.ru/faq/obc34/obcrele2.jpg
http://www.prussianmotors.com/eBay/DSC_1087.jpg
http://www.prussianmotors.com/eBay/DSC_1088.jpg

[myles]

any e34/e32 with an obc and without dwa will have one. any cars with dwa will have a larger module plugged into the same wires.

[pundit]

I picked up an OBC auxiliary horn relay from Peninsula BMW this afternoon.
I now have a working OBC in my 525i Touring!
Thank's for your help Myles.

Until I managed to find an actual photo of the horn relay I was visualising something quite different..
The s/h relay cost me $35.
It was out of an E32.
They initially wanted $75 for one but that's more than a new one so I let him know and he dropped the price.
The next thing to fit is the stalk.

[myles]

good work.... ready for some weekend driving

[genphreak]

Heh, I wonder if this means a horn relay can be used to replace a DWA IV unit. People remove the things, someone did in mine and I had to buy a DWA IV from the US. $25 and it brought up my OBC again. The PO had installed a keyfob for the central locking, but this still works with the DWA unit... I wonder if I'll find out why it was removed at the wrong time and in the wrong place, one day. Some peeps remove the DWA unit when having false-alarms. Mine has a bay-mounted dealer fitted BMW alarm, it is long dead, so has to come out one day soon.

I have yet to fit the stalk in mine... did u swap the coding so the L/100 will work properly for the M50?

Keep up the good work Pundit!

[pundit]

Re coding are you referring to the coding plug?

The 535i's OBC has no coding plug within the unit itself and, in my case, doesn't need to have one fitted.
The OBC gets the vehicle info from the coding plug fitted to the rear of the instrument cluster in the higher spec E34's ie models above 518's/520's.

Both tanks are 80 litres though my 535i was notoriously inaccurate below about 1/3rd of a tank.
There is a procedure for calibrating the OBC so I will do this in order to make certain it is accurate.

The DWA can be replaced by the OBC auxiliary horn relay (p/n 65811378027).

Although the basic digital clock/date/memo/temp unit will function without it, the OBC requires it in order to get power to pin 17

You can jumper a link across from pin 9 (power) to pin 17 but I prefer to avoid altering the factory wiring if possible otherwise things can get messy and result in gremlins popping up down the track.
This was the case with the shoddily fitted aftermarket keyless/immobilser unit.
I've had no more non-starting and random central locking 'antics' since I removed it!

The OBC auxiliary relay is not your common 1" cube type relay as I thought it was.
The relay itself is mounted mounted on a PCB inside a retangular plastic case with a fuse fitted to it.

The 4 way connector cable is located under the rear seat on the left and will be hidden between the seat base and the General Module/Relay Module/Fuse assembly bracket.

The OBC auxiliary horn relay is listed as item 12 in this pic (p/n 65811378027)
You may find it is easier to get one from a wrecked E32 as they tend to have OBC's fitted as standard equipment and are identical to the E34 versions.

http://www.realoem.com/bmw/diagrams/b/x/261.png

[AlpinaMan]

simply put, the obc from a 535 will not work on the M50 525 or m20 525. find one from a 525.

[pundit]

simply put, the obc from a 535 will not work on the M50 525 or m20 525. find one from a 525.

Not according to this...

BMW E34 Website (http://www.bmwe34.net/E34main/Upgrade/OBC.htm)

"....All the OBC IV's out of higher spec cars eg.525, 535, etc (without coding plug socket's) are technically dumb on their own as they have no information about the car's engine type, etc..."

The OBC IV's get the required vehicle information from the coding plug fitted to the vehicles instrument cluster.

In the case of the 518's and 520's which are not fitted with coding plugs a coding plug to suit these vehicles needs to be purchased from BMW and then must be fitted to the OBC itself to ensure correct readings.