Obc range, consumption, speed

Post Fri Aug 01, 2014 8:07 am

I've searched and found similar questions asked but never an answer...

My 13 button once works fine apart from range, consumption and speed. The speedo and fuel dial both work so data is being sent to the clocks just not the obc.

What can I do to remedy this issue?

Post Fri Aug 01, 2014 8:46 am

You haven't told us what the issue is, so there's not much I can reconmend.

Post Fri Aug 01, 2014 10:05 am

The Range, Consumption and Speed do not provide any data, they remain at zero, sorry thought it was clear but can see I didnt explain

Post Fri Aug 01, 2014 10:56 am

Does the obc have a coding plug in it? It might not if retro fitted by someone.

Post Fri Aug 01, 2014 12:04 pm

It's original to the car

Post Fri Aug 01, 2014 12:50 pm

The connection between the OBC and the dash cluster is very simple, but some of the wiring may have been disturbed if the car has had an aftermarket stereo or alarm fitted at one point.

My first guess would be the single green wire that plugs into the back of the dash cluster. If that's come loose, the OBC won't have access to any speed info, and therefore won't be able to make other calculations either.

Post Fri Aug 01, 2014 2:32 pm

Cheers will take a look at that and see if I can fix it up.

Appreciate your help

Post Fri Aug 01, 2014 2:59 pm

E30Worx wrote:Cheers will take a look at that and see if I can fix it up.

Appreciate your help

Mine's the same as yours, I'll be taking a look at it this weekend too, cheers for the post and cheers GRRR for the info.

Post Tue Aug 05, 2014 10:53 am

By single green wire do you mean the one that has a plug not far from where the loom connects to the OBC itself?

I have recently retrofitted an OBC from a 325i se to a 316i which had this problem on the 325 and now also the 316. All connections availiable are plugged in and everything works except for the speed, range mpg. and code but that's alright...

Post Tue Aug 05, 2014 11:54 am

All the data and power the OBC needs to work, except for ext. temp., passes along the loom from the yellow multiplug on the instrument cluster to the green multiplug on the OBC. If all wiring, except the bit between these two plugs is chopped from the loom, all you will lose is the ext. temp display, the near useless immobilizer, the gong and the remote control from the column stalk.

Post Tue Aug 05, 2014 7:19 pm

Does the relay module have any part in the fuel/speed computations?

At least for me it would be unrealistic to say its the cluster as the mpg gauge works on both cars.

Any ideas where to test? I will send a guy I know a message who has just brought a 325i to see if I his works and test components with my wiring.

Post Wed Aug 06, 2014 2:09 pm

I have exactly the same problem, my OBC was working fine and has just stopped with no obvious fault.

Unable to find the fault so far, loom is ok, clocks are ok.

Not a clue as to the reason for the fault, it just stopped receiving data from the dash.

Everything seems to function ok, including the indicator stalk .

Post Sun Aug 10, 2014 8:25 pm

I have just spend the last few days getting to the bottom of this and I now know what is going on.

There seems to be a few common symptoms to this from searching around on the net.

Symptoms seem to be:
1. Clock on the obc works so does the back light
2. obc will switch to all modes but does not display any data
3. Dash works fine
4. SI board works fine
5. Loom has perfect continuity.
6. Pressing 1+1000 or 1+100 will not show the coding plug type or the fuel remaining in L
7. 12v, ~10v and 5v can be detected at the OBC end of the loom with the ignition on

Bases on that I pulled my OBC apart and started checking things.

Turns out the bad news is the capacitor on the main OBC board will have burst taking a trace on the top printed circuit out when it went.
If all of the above holds true then this is the problem, it also explains why no one has found it before as I cannot find a documented OBC strip for the e30/e28 obc anywhere.

Good news is it is fixable.

Mine is now a happy working chappy reporting all things like it used to.
More to come when I have pulled the pictures off my phone.

Procedure is fairly simple but not for those with shaky hands or limited soldering experience. Willing to do a few if this turns out to be common.

Post Sun Aug 10, 2014 9:59 pm

HairyScreech wrote:

Turns out the bad news is the capacitor on the main OBC board will have burst taking a trace on the top printed circuit out when it went.

That's not bad news - any fault on a circuit board that gives itself away by a bit of obvious physical damage is good news in my book, even if it does require a bit of cleaning up afterwards.
Well done on getting this far. Keep us posted.

Post Sun Aug 10, 2014 11:58 pm

Will do, took quite a few pictures through out but will have to pull them off the phone.

There must be quite a few units with this problem hanging about.

Having done a back light repair and having a unit with no LCD issues I was loath to just write it off.

Post Mon Aug 11, 2014 1:11 pm

Ok, here comes the pictures.

To open the OBC requires removal of the coding plug and two screws shown here:

You can then get a spudger in and pop the rest of the case.

You will be faced with this:

First thing that struck me as after popping the case:

To get the buttons/face plate off there are pins that go through the two blue connectors and the white plastic connector strip in the centre.
This needs a fair bit of levering/pulling so care is required and it would be very easy to kill the unit at this point.

There are two plastic stand offs that space the boards, remove the screws and pull them out with some pliers.

A better look at that cap.

Unsolder the terminals and you can just about twist/squeeze the cap out of the gap, there is a little wiggle in the boards to give you room but its tight and easy to damage the boards again.

After unsoldering one terminal this is what happend:

Seems that cap was worse than it looked.

Kind of explains the sudden failure.

Not having a 16v 220uF cap about I put 3 16v 100uF caps in parallel just to check it (cause everyone pulls spare caps of old pc motherboards and hangs on to them right? right? no just me then.

)

Put all this back into the car and found it was still dead. bollocks.

Went back into the unit and load tested the caps and started checking components one at a time only to spot this on my way through.

Seems when the cap goes it takes this trace out.
Trouble is its all tiny. Normal stanley blade sat on top to give an idea of size.

No chance of repairing that on the board, I don't even think I have a miniature brush fine enough to paint the trace.

Solution: A quick jumper.

Put it all back together and:

Its all quite simple but you do need a steady hand and a soldering iron the size of Justin Biebers todger to do it.
I have a source of the correct size caps needed and I might investigate a fuse that could be added to the jumper to prevent the next weakest link going should a cap reblow.

When I ordered bulbs for mine I accidentally ordered 5x the number I needed and I have the correct size caps now in stock so if anyone wants their bulbs done and the caps replaced then let me know.

Post Mon Aug 11, 2014 1:22 pm

Congrqats on a nice bit of component level fault finding! If you think the tracks on that are tiny, try working on something made in the last few years!! You can hardly see the components themselves nowadays, let alone the PCB tracks.
Wire link is the correct way of repairing that kind of damage, and adding fuses would be overkill. It's not going to happen again with a decent quality new cap. fitted.

Post Mon Aug 11, 2014 1:35 pm

Brianmoooore wrote:Congrqats on a nice bit of component level fault finding! If you think the tracks on that are tiny, try working on something made in the last few years!! You can hardly see the components themselves nowadays, let alone the PCB tracks.
Wire link is the correct way of repairing that kind of damage, and adding fuses would be overkill. It's not going to happen again with a decent quality new cap. fitted.

Oh I know, modern stuff is just not repairable really, I have managed to do SMDs on PC boards before but its like brain surgery with a masonry drill.
I'm guessing you have recently been inside a mobile phone?

Older Solder through boards are where I stop now, simple rugged and repairable, there will be no classics in 30 years as the current crop of modern cars will all be scrap with unrepairable electronics.

Re: Jumper, it is about 5x the size of the trace on the board which I don't really like doing as it moves the weak link.
Granted it should not happen again but there is no saying if the cap caused the damage or a V spike caused the cap and the trace.
Your right though it is overkill to fuse, I just like to add fail safes when I can.

The question is do I go for a ceramic cap to replace it, electrolytics are good cheep capacitance but a modern ceramic should be more than man enough and less likely to fail?

Post Mon Aug 11, 2014 6:22 pm

I'll be cracking mine open in good time to see if it's the same problem and will update here.

Thank you very much, Hairy.

Post Mon Aug 11, 2014 6:34 pm

Easy way to check is to see if the pins in the green plug give 12v ~10v and 5v. If your SI lights reset and if the obc will dispaly the fuel in the tank and the coding plug type.

If there is voltage at the plug and the obc wont display either of the fuel or coding plug then its the same issue.

Press 1+1000 and 1+100 on the obc to find out.

The only reason it should not report the coding plug type is if its burnt out.

Post Mon Aug 11, 2014 6:43 pm

Not entirely sure what you meant with your instructions but push pressing 1000, 100 and 1 in all the combinations I could didn't change anything on it. I also have the exact same symptoms as you.

Any of those capacitors for sale?

Post Mon Aug 11, 2014 7:21 pm

You should be able to press 1000 and 1 at the same time and read out the coding plug type (see 4 . 6 typ picture) and 100 and 1 at the same time gives the fuel remaining in L.

If you have tried all combinations then yes its the same issue.

I can send you a link to the right capacitors/maybe post some up or I could do your caps, the trace and put new back light bulbs in for £25 if you post it down.