My OBC flashes oddball sequences of numbers and letters (and occasionally fragments of numbers), won't keep time correctly (the clock usually doesn't work at all, but when it does it picks up a couple of hours per day), causes the horn to honk at unpredictable times (but not totally unpredictable -- it likes crowds), is unresponsive to the buttons on the front panel, and just generally acts buggy.

So I bought a known good OBC to replace it. But when I swapped the new one in, I was surprised to find that it acts just like the original. If the original is repeating the sequence, say, "1 d 2 0" (which it was doing today - do these mean anything?), I can unplug it and move the connector over to the new one, and the new one will also display "1 d 2 0" -- the exact same thing. Or if the original flashes four dots, the new one flashes four dots. Pretty weird, huh? This tells me the problem probably isn't in the dash unit OBC (since it's doubtful they're both bad) but instead is somewhere upstream.

Which leads me to my question -- is there a master OBC computer located apart from the little unit in the dash? I know there's an electronic box of some kind under the dash to the left of the steering wheel that holds a fuse for the OBC (I've been into it once to replace the fuse). Does any processing for the OBC happen there? If so, I'm thinking that box might need replacing.

You guys have any thoughts on this?

Thanks!

What year is your car? (Maybe add it to your car info).

The unit in the center console is just a display, the computer is under the drivers side kick panel.

Download a PDF file of the ETM for your year car (http://wedophones.com/BMWManualsLead.htm)

Okay, that confirms what I suspected. The problem is probably in the unit behind the kick panel. That's good news in a way -- it's easier to get to than the display unit, which from what I've read can be a chore to pull.

The car is an '84 633csi. I won it on eBay a few weeks back for $3k with 105k miles. It's gorgeous but it's really been nickel and diming me with little problems like this. And some not so little -- I replaced the driveshaft last weekend. I think I've about got it "stabilized" now, though.

But I love the car. The great thing about these classic Sixes is that you almost always have the coolest car in the parking lot.

My 83 OBC is doin the same thing. If you computer fixes the problem, let me know!

My relay under the kick panel is also clicking away like no tomorrow when the display flashes some funky stuff. I just thought the car was trying to tell me something.

-Jeff

Yeah, I'll be sure to post a follow up.

The thing about the OBC is that it has its tentacles in some important places. The horn circuitry for one, and after looking at the ETM I see that it also controls a starter kill switch that's part of the alarm system. So it has the potential to be very mischevious.

I'm pretty motivated to get this done. It'll probably be in the next week or so. I'm seeing OBC computers on eBay for around $50.

I had what sounds like a similar problem with my '88 735i (E32). I had a number of glitches that I could live with (fast clock, some other computer display problems) for quite a while, but last week I left the flashers on and the car needed a boost. As a result, I got the dreaded PPPP in the OBC, as well as lots of funky stuff on the cluster display. Since the OBC is connected to many other systems, I assume that the problem is not strictly OBC-related.

The solution was simple: disconnect the battery for about an hour. Everything reset, and it all works fine - and, believe it or not, the tranny shifts more smoothly and the engine seems to run with a better idle. The E32s have an "adaptive" system, and it tends to get wonky after a while and needs to be re-set. I've seen suggestions that you should remove both battery terminals and jump (short) the cables (NOT the battery terminals themselves of course) for about 10 min, and that will erase all of the adaptive stuff.

Now, all that said, I don't know how similar the older OBCII for an '84 633 would be. However, it won't hurt to at least disconnect the battery for a while and give it a try.

Thanks. I'll give the battery disconnect thing a try.

Funny that you got the fast clock too. I wonder what would would cause that? It's a really strange symptom. If anything I would expect it to run slow, but maybe that's just me picturing its workings in an analog kind of way, like its spring winding down or something.

BTW, does anyone know if there's a manual for the OBC or something similar posted on the net?

Oh yeah, mine is actually an OBCI. I think the OBCII started with the 635csi.

Let us know if the disconnect works.

I should have guessed OBCI - my '84 M635 has the OBCI.

Ill try the disconnect too. Ill disconnect it tomorrow morning and see how things go when i get back at the end of the day.

-Jeff

Okay, tried the battery disconnect trick, but no luck. The OBC is still the crazy old man it was before. Thanks for the suggestion though -- it would've been great if that had worked.

I took another look at eBay and unfortunately didn't see any OBC master computers (the box in the driver kick panel) for 633's, only for a 635. But Vines Automotive (a bimmer recycler here in AL) has one for $125. They're letting me return the OBC display unit that I had bought earlier from them for $35 (which it turned out I didn't need) so it'll only feel like $90, which is tolerable (barely). Being that Vines is almost local the computer should arrive Thursday-ish, and I'll have it in before the weekend. So more info coming soon hopefully.

After this I'm going to tackle putting in a new stereo. I've never dealt with a car with an outboard amplifier, so it could be interesting.

One more thing to try:

Turn the key to the first position, then press the CODE button, and then use a paper clip or the tip of a ball point pen to press and hold the small recessed button on the lower right of the unit. After a second or two, either the LED in the M MPH button will flash once or the display flashes, I can't remember which, and the OBC is reset. All memory is wiped out, so you'll have to reset the date and time.

Unfortunately I think that only works for the OBCII. The OBCI, if I'm remembering right, doesn't have the recessed button. I'll doublecheck mine though.

I checked my OBCI display unit and it does not have the recessed reset button like the OBCII.

I've got the head unit on order from Vines. Should be here Thursday. Out of curiosity I checked Bavarian Auto Recyclers to see how much they wanted for theirs -- $250. Thanks Vines ($125)!

My 83 OBC is doin the same thing. If you computer fixes the problem, let me know!

My relay under the kick panel is also clicking away like no tomorrow when the display flashes some funky stuff. I just thought the car was trying to tell me something.

-Jeff
Jeff, my rely clicks as well...I fixed it by saying "huh" and shrugging my shoulders...

I checked my OBCI display unit and it does not have the recessed reset button like the OBCII.

I've got the head unit on order from Vines. Should be here Thursday. Out of curiosity I checked Bavarian Auto Recyclers to see how much they wanted for theirs -- $250. Thanks Vines ($125)!

Just an FYI: you should post here when you are needing something. I had been following this thread but did not want to jump in just offering parts but many of us here have plenty of spares; I know I do. Did you get the display unit or the control unit?

Todd

Jeff, my rely clicks as well...I fixed it by saying "huh" and shrugging my shoulders...

haha, thats what ive been doing to, but im getting tired of watching my interior light up like the griswalds' place on christmas!

-Jeff

Thanks for the advice, Todd. I hadn't thought of checking with you guys on parts. Makes sense, though.

The part I've ordered from Vines is the OBC control unit. I tried a new display unit, but when I plugged it in it acted just like the old one. That told me the problem was elsewere, and I'm feeling pretty confident that it's the control unit (which I've also referred to on this thread as the "head unit" (Vines' term for it) and the "box in the driver kick panel". For the sake of keeping terms consistent I'll call it the control unit from here forward).

I have accumilated so many parts over the years, that it is nice to be able to assist: I also really enjoy trading. I have also offered parts to people before to help track down problems so unnecessary money is not spent. Most likely you are correct in the control/head unit being the issue. The $250 price is just crazy but you also have to be careful with the cheap eBay parts. I can not test all of my parts as they may have beeen pulled from wrecked cars that I parted out but, I will replace them or allow them to be tried.

Todd

No dice for me on letting the battery be disconnected.

-Jeff

Good news! The new control unit solved the problem. All the OBC functions work now, and no more honking fits. I love it when stuff works. It's little victories like these that make being a car nut so much fun.

One thing I notice, though, is that my outside TEMP reading stays pegged at 122 degrees, which I'd almost bet is the max end of the scale, which probably means the sensor has failed short or open. I looked around for the sensor in the ventilation system intake area at the base of the windshield but didn't see anything interesting except for a wire pair that had been snipped. Makes me wonder if maybe it was connected there at one time. Does anyone know where the outside temp sensor is supposed to be located and what it looks like?

Also, plugged into a socket on the side the OBC control unit is a little thing called a code plug. It's a mini PC board that somehow configures the operation of the computer. Like I'm guessing it "tunes" the formulas used to calculate range and MPG etc to your particular engine configuration or whatever (and maybe gas tank size). So the question is, which code plug to use with the new control unit -- the one that came with it, or the old one? I figured the old one since it would be matched to the engine/relevant systems that came with the car. It seems to be working fine, but does anyone know the rule of thumb on this?

And finally, a tip. When you're pulling the connectors from the control unit (there's a yellow one and a blue one), be aware that they weren't designed to pull straight out. Instead, you should swing/pivot the connector out by pulling on the left tab only, with the right tab acting as a hinge. Same deal when you're reconnecting -- hook the right tab into its slot, then press in on the left tab and it will pivot into place. This will make sense when you're actually doing it.

One other thing while I'm thinking about it. When everything's hooked up you'll get four blinking dots "...." on the display. The clock should be set now by pressing the CLOCK button three times, then entering the time with the number keys. (Actually, before you enter the time you should select AM or PM. The default is AM; for PM hold the CLOCK button down till the little light toggles to PM. Then enter the time.) When you're done, press START and the clock will start running.

The OBC temp sensor is in a hole in the front spoiler on the lower left side.

Thanks. I found the spot behind the spoiler and sure enough -- the connector is there, but the sensor is AWOL.

Speaking of temperature sensors, should there be a noticeable vacuum on the hose that connects to the interior temp sensor housing for the climate control system? I was fiddling with mine while I had the kick panel out and noticed that it seems have either no vacuum or a vacuum too subtle to detect with a finger over the end. It makes me wonder if the climate control system is getting a good input.

They want $75 for the OAT sensor! Somewhere on the net I ran across a site with instructions on how to make one. An LM344 IC chip costs $4 with a few resistors and capacitors and a tube with some potting compound and you're all set. Now I can' find the site!

Make sure the white nylon line from the interior temp sensor is connected to the intake manifold. The small black hose that connects the white nylon line to the intake manifold has a flow restrictor in it , so I guess there wouldn't be a lot of flow. After all you wouldn't want too big of a "vacuum Leak".

I like the DIY idea, but I've spotted a sensor on eBay for $10.:redspot Hopefully it won't get bid up much.

I rechecked the vacuum on the line (there was none), then traced it back into the engine bay. Turns out there's a mangled section that's letting the vacuum escape. It's funny -- I think the perp was a squirrel. According to the PO, a squirrel had taken up residence under the hood while he had had the car in storage. I've noticed little teeth marks on other plastic plastic parts around the engine; it looks like he got to this vacuum line too.

But, another mystery solved. Once I get this fixed, maybe my automatic climate control system will be more automatic (though I don't think I've ever experienced an automatic system that doesn't still require regular knob twiddling -- it's just that the time between twiddles is longer.)

They want $75 for the OAT sensor! Somewhere on the net I ran across a site with instructions on how to make one. An LM344 IC chip costs $4 with a few resistors and capacitors and a tube with some potting compound and you're all set. Now I can' find the site!

FYI, I found the site for making the temp probe at the BCG Tech Library:

http://www.normgrills.net/bcg/Electrical.html#anchor30842949

Pretty cool. I wound up getting the $10 one on eBay, but it's good info for the archives.

In squirrel country, (maybe mice too) when storing your car under cover outside for the winter, put some mothballs in some socks and put this smelly package on top of each wheel and on top of the engine (or in the engine compartment) and it will help keep the squirrels away. I haven't tried this myself but did read it elsewhere. I've had problems with critters making a nest in the heater in my truck which was allowed to just sit for a while outside! Be sure to remove the mothball packages before starting the engine in the spring!

Yeah, squirrels love engines. Lots of little hiding spots for their nuts and stuff. For about a week after I bought this Six, I had nut shells blowing out of my A/C vents. One still blows out every now and then. My step mom had a Camry that started making an incredible stinking smell from under the hood. Turned out a squirrel that was stashing catfood around the exhaust manifold.

But those cute fluffy tails -- they can get away with anything!

I am resurrecting this thread....

The OBC in my vehicle worked fine for the first month or 2 or ownership, however, in the last couple of weeks, not so much. The first problem I noticed was that the unit reset itself. Units were changed, and all info was zeroed out. I reset it, and it worked fine. This happened a couple more times, and I simply reset it (wishful thinking). Last night, i got in the vehicle and the display was blank. It was still lit, but none of the buttons functioned. I have not tried the reset or battery procedure. I will try that this evening.

Any suggestions? I assume I have the OBCII. Thanks!

ed

Clean the grounds (Brown wires). On the inner fender next to the battery, on the left side of the head at the back and lastly, next to the steering column under driver's kick panel.