OBC and Coding help please.

[ss2115]

I've followed the various internet instructions to retrofit a full OBC to my 1993 525i Touring and although its working, I need some help.

I was aware that its had a drivers side prang but the repair is very good and it tracks straight and true.
It came with the digital clock with the outside temp only.
I purchased a full OBC from eBay that supposedly came out of a late model 5-series but they didn't say what.

I've fitted it and it's working straight up - sort of.
I suspect the fuel and range figures and such to be inaccurate.
Everything else seems to be okay.
From research about the retrofit, I gather that on my vehicle, the coding board is part of the instrument cluster.

I've come to the conclusion that my steering column and possibly the instrument cluster have been replaced by used parts as part of the accident repair.
I think so because for a start, I have the push button on the cruise control to operate the OBC in the dashboard (not that's its working) and if the car originally came from the factory with just the digital clock version, then there wouldn't be a need for it - right?

Then also I've unlocked the OBC and gone through the firmware version stuff mentioned in the articles.
Mine comes up 5-6 1991.
According to the internet articles, its for a 535i (I guess a 1991 model perhaps?)

This is where I come unstuck.
Is this firmware confirmation for the OBC itself, or for the coding board?
If its for the OBC, then I shouldn't have a problem I think because the coding board is supposed to supply the correct engine size, fuel tank size, tyre diameter etc etc to the OBC for my car.
However, if that's the coding board information, then the OBC is getting the wrong info for my car and its understandable that the figures will be incorrect.
(e.g.: it tells me I have a range remaining of 528klms, but the tank is at 2/3rds and a full tank hasn't given me more than 420 klms yet).

If I need to change the coding board, is it possible to do so or is it so integrated with the instrument cluster that its not possible?

I realise that by using the correction factor, it may be possible to correct the fuel consumption figures, but it still won't give me correct range or fuel remaining or such useful info. Also I read that if the car isn't driven for a couple of days, the correction factor will default back. (as I leave the car at the airport for up to a week at a time, this won't suit me).

Next problem then is the switch not working.
I haven't striped out under the steering column to see if its plugged in (and obviously I will do so) but there's no reason to think it wouldn't be as a mechanic replacing a steering column from a wrecker would be inclined to plug in everything that had a matching plug.
Are there any other tricks to getting the dash display to work before I take the lower dash apart?

Hoping someone can assist.

[BMWDriver]

I'm a bit confused in reading your post, but I take it you want to show information on the instrument cluster coming from the OBC. To program this feature is done by pressing for 5 seconds inwards on the turn signal lever, and then selecting one info button on the OBC, pressing the turn signal again and selecting another info to display, and so on. I forget how to end your selections, either it's the s/r button on the OBC or you press the lever again instead of selecting another OBC function.

Then as you press the lever inwards again, it begins to show the info in the order you selected each time you press inwards.

Fuel estimates : One thing to note is that often the gas level indicator becomes innacurate after some years. As an example, I have a variation of about minus 15-20 liters on mine, which shows me an empty tank way before time - when I still have about 20 liters. This puts the capacitors at fault on my instrument cluster. I have not changed them all yet. When it's full though, it shows full. It just goes down quicker than it should afterwards.

Your gas tank carries 80 liters, plus a reserve I should think. You may want to take that into account for the estimates of the OBC, and look at how many liters go in when you do fill her up. The OBC will also change its estimates on the highway, as compared to city driving, and probably also based on the average of fuel consumption. For example, as I drove for about 15 minutes in town, the estimates changed bit by bit once I hit the highway, giving a longer and longer range. If I hit the s/r button once on the highway, it makes new calculations immediately.

As far as manufacturing goes, it's not worth to put a different lever on a steering column for an optional feature, especially if that switch is not an obvious one. Better to have as many common parts as possible. Does not mean I'm right, but that's how I figure it.

[ss2115]

I'm a bit confused in reading your post, but I take it you want to show information on the instrument cluster coming from the OBC. To program this feature is done by pressing for 5 seconds inwards on the turn signal lever, and then selecting one info button on the OBC, pressing the turn signal again and selecting another info to display, and so on. I forget how to end your selections, either it's the s/r button on the OBC or you press the lever again instead of selecting another OBC function.

Then as you press the lever inwards again, it begins to show the info in the order you selected each time you press inwards.

Fuel estimates : One thing to note is that often the gas level indicator becomes innacurate after some years. As an example, I have a variation of about minus 15-20 liters on mine, which shows me an empty tank way before time - when I still have about 20 liters. This puts the capacitors at fault on my instrument cluster. I have not changed them all yet. When it's full though, it shows full. It just goes down quicker than it should afterwards.

Your gas tank carries 80 liters, plus a reserve I should think. You may want to take that into account for the estimates of the OBC, and look at how many liters go in when you do fill her up. The OBC will also change its estimates on the highway, as compared to city driving, and probably also based on the average of fuel consumption. For example, as I drove for about 15 minutes in town, the estimates changed bit by bit once I hit the highway, giving a longer and longer range. If I hit the s/r button once on the highway, it makes new calculations immediately.

As far as manufacturing goes, it's not worth to put a different lever on a steering column for an optional feature, especially if that switch is not an obvious one. Better to have as many common parts as possible. Does not mean I'm right, but that's how I figure it.

Hi BMWDriver and thank you for the reply.

Button: Yes - thats what I'm trying to do, but maybe I've got the incorrect button. On my car, the indicator doesn't push inwards. However, the cruise control lever does. At first I thought this would turn the cruise control on/off, but there's no indicator or light or anything that says the cruise is on or off and in fact it is actually on all the time and can be used at any time (subject to speed) whether the button is pushed or not.
Then someone told me that the switch was to get the OBC reading up on the dash, so I assumed they were correct.

OBC: My car had only the basic digital clock and outside temp where the OBC is mounted. I purchased a full OBC off eBay and followed an article on retrofitting it to a car that doesn't have it from the factory.
It was a succesful fit and the OBC is displaying all the various functions, but is inaccurate.
I don't think its that the car is old and that the fuel sender in the tank is worn and inaccurate - I believe its due to my car having the incorrect coding plug to send the right information such as fuel tank size, wheel diameter, speedo sensor etc to the OBC and so its making its calculations on incorrect information.

What I'm hoping someone can assist me with is if the coding plug on the back of the instrument cluster is able to be changed or if its integrated, and then if they agree with my diagnosis, or can head me in the right direction if I'm wrong.

[LunatiC]

On my car, the indicator doesn't push inwards. However, the cruise control lever does. At first I thought this would turn the cruise control on/off, but there's no indicator or light or anything that says the cruise is on or off and in fact it is actually on all the time and can be used at any time (subject to speed) whether the button is pushed or not.

No, the Cruise control lever only controls the cruise control and nothing else. Pressing it in will resume the speed that it was previously set at (only up until the last time the car was started). In the E34 there are no indicator lights or any other indication that cruise control has been switched on.

Then someone told me that the switch was to get the OBC reading up on the dash, so I assumed they were correct.

The OBC display switch is only on the indicator stalk. If you don't have an indicator stalk that presses "in", then you don't have one with an OBC switch. Additionally, the OBC indicator stalks have a little 'BC' label on them.

It was a succesful fit and the OBC is displaying all the various functions, but is inaccurate.

It was probably from a different model to what you have. I have a 520i OBC in my 525i, as I used to only have digital clock/temp so its estimates for fuel range is optimistic.

What I'm hoping someone can assist me with is if the coding plug on the back of the instrument cluster is able to be changed or if its integrated, and then if they agree with my diagnosis, or can head me in the right direction if I'm wrong.

I haven't done the coding plug swap myself, but I always thought the plug was located behind the OBC unit and not behind the instrument cluster.

[ss2115]

No, the Cruise control lever only controls the cruise control and nothing else. Pressing it in will resume the speed that it was previously set at (only up until the last time the car was started). In the E34 there are no indicator lights or any other indication that cruise control has been switched on.



The OBC display switch is only on the indicator stalk. If you don't have an indicator stalk that presses "in", then you don't have one with an OBC switch. Additionally, the OBC indicator stalks have a little 'BC' label on them.


It was probably from a different model to what you have. I have a 520i OBC in my 525i, as I used to only have digital clock/temp so its estimates for fuel range is optimistic.


I haven't done the coding plug swap myself, but I always thought the plug was located behind the OBC unit and not behind the instrument cluster.

Thanks for clearing that up for me.

Regards the plug, its not 100% clear to me either, but from what I think the various articles are saying is that on the 518 and 520's, the coding plug fitted in to a slot on the back of the OBC, but on the 525 to 535 the coding plug was fitted to the instrument cluster and the OBC factory fitted didn't have the code plug slot.

This seems to gel with a lot of the photo's of OBC's I've seen as some have the green coding plug fitted on to the back of the OBC just immediately under the wiring plug, and others like mine don't have this space or slot for the coding plug.

Then also in one of the retrofit articles I studied, the owner had a 520 but aquired an OBC from a 525 (without the coding plug slot on the back) and he describes how he purchased the correct coding plug for his car, took it apart and soldered it directly to the OBC board and it all worked fine and was accurate for his car.

So where there's a will, there's a way and I just need someone who's done or come across this retrofit before and knows what to do.

[ss2115]

For anyone following this post, a nice man in the USA confirmed that the coding plug is indeed a seperate component and can be plugged/unplugged and transfered to different cars and purchased through BMW.

The bad news is they are now terribly expensive - ridiculously so.
I've had a price from here in Oz and also a price from the USA - the USA is slightly better.

The article I've been following said he got his from the dealer in the UK for 20 pounds.

Is there any nice fellow living in the UK that would like to inquire for me of the price on a coding plug?
If its cheap enough I'd forward my VIN number and details and would make it worthwhile obtaining it and sending it to me. I'd pay by PayPal.