MyE28.com

I have a very strange situation that I'm hoping someone may know the answer to: My odometer has suddenly started spinning double time!

I noticed it today when i drove to the airport, which is about 40 miles according to Google maps. However, my odometer read 77 miles for the same distance??!! What the heck could be going on? My speedometer appears to be accurate, perhaps a tiny bit off, but nothing as far off as would be needed to have double the miles.

Any ideas????

I did recently change tires and rims. I went from a 205/60/15 to a 225/50/16. But, I dont think the diameter difference is all the great between these two. Also, i have an automatic trans if that gives any clues.

I'm going to bet there's something amiss with the stepper motor circuit, which is causing it to spin too quickly. I don't see it being a gear issue. I'd almost think you have the km gear in there, but if you didn't put it in, then that wouldn't make sense. Still, 77km is 47.8 miles.

Well, I certainly didn't put any gears in it. I haven't even pulled the speedo cluster. Funny thing is, is that its been working fine for years, or at least i thought it was. Seems i would have noticed if it wasn't. Maybe i have half as many miles as i think i do? Hmmm.

The e28 speedometer uses the UAF 2115 Speedometer and Mileage Indicator. This is the integrated circuit on the small circuit board that's part of the speedometer assembly. My guess is that your problem is with pin 11 on this chip.

The UAF 2115 appears to be a 14-pin IC, where the middle pin on each side is extra-wide. Actually, the middle pins are connected together, and both are called pin 13. So it's actually a 13-pin IC.

Like most ICs, the UAF 2115 has a notch at one end. The pin to the left of the slot (when the slotted end is facing up and the pins are facing away from you) is pin 1, and the pin to the right is pin 12. The pin next to pin 12 is pin 11- the pin you care about.

If pin 11 is connected to pin 10, the chip counts 128 pulses for each pulse is sends to the odometer stepper motor. This is the slowest setting.

If pin 11 is grounded (pin 13- the giant double-pin), the chip counts 64 pulses. This is the middle setting.

If pin 11 is floating, the chip counts 32 pulses. This is the fastest setting.

So my guess is that pin 11 is supposed to be grounded, and the connection has failed. Break out your soldering iron.

When this happened to my speedometer, it turned out that a capacitor on the circuit board had failed as well. I replaced it at the same time.

edited 4/29/2009 to clarify chip orientation when identifying pin 11

How do you know this stuff?

Ron is that good.

wkohler wrote:Ron is that good.

Ya, he's pretty damn good.

wkohler wrote:Ron is that good.

I know my way around a soldering iron, meter and schematic, but I agree, Ron is that good. I'm not easily impressed, but he's done it more than once.

So if an odometer was turning at say 7/10 speed, all of a sudden, what do you suppose that could be.

wow. I'm in awe. I'll pull my cluster and check it out. Thanks!

RonW wrote:The e28 speedometer uses the UAF 2115 Speedometer and Mileage Indicator. This is the integrated circuit on the small circuit board that's part of the speedometer assembly. My guess is that your problem is with pin 11 on this chip.

The UAF 2115 appears to be a 14-pin IC, where the middle pin on each side is extra-wide. Actually, the middle pins are connected together, and both are called pin 13. So it's actually a 13-pin IC.

Like most ICs, the UAF 2115 has a notch at one end. The pin to the left of the slot is pin 1, and the pin to the right is pin 12. The pin next to pin 12 is pin 11- the pin you care about.

If pin 11 is connected to pin 10, the chip counts 128 pulses for each pulse is sends to the odometer stepper motor. This is the slowest setting.

If pin 11 is grounded (pin 13- the giant double-pin), the chip counts 64 pulses. This is the middle setting.

If pin 11 is floating, the chip counts 32 pulses. This is the fastest setting.

So my guess is that pin 11 is supposed to be grounded, and the connection has failed. Break out your soldering iron.

When this happened to my speedometer, it turned out that a capacitor on the circuit board had failed as well. I replaced it at the same time.

Gladiola!...sir, thats amazing. Might I get your opinion on my 88eta speedo that is accurate to 67 mph and just stays there, then decelerates normally? Is the stepper-motor a user replaceable item?
Thanks in advance.

moengel wrote:How do you know this stuff?

The schematic is in the datasheet for the chip, which also explains the behavior of pin 11.

V1cut wrote:Might I get your opinion on my 88eta speedo that is accurate to 67 mph and just stays there, then decelerates normally? Is the stepper-motor a user replaceable item?
Thanks in advance.

If it's accurate to 67 mph, then it's likely a physical problem- something jamming the needle. Can you move it by hand beyond that point?

The stepper motor isn't a single component. It's a couple of coils of wire, connected to the circuit board with three wires. If any one of the wires is broken, the odometer won't move.

landspeed wrote:So if an odometer was turning at say 7/10 speed, all of a sudden, what do you suppose that could be.

A broken gear. Odometergears.com to the rescue, of course.

RonW wrote:

V1cut wrote:Might I get your opinion on my 88eta speedo that is accurate to 67 mph and just stays there, then decelerates normally? Is the stepper-motor a user replaceable item?
Thanks in advance.

If it's accurate to 67 mph, then it's likely a physical problem- something jamming the needle. Can you move it by hand beyond that point?

The stepper motor isn't a single component. It's a couple of coils of wire, connected to the circuit board with three wires. If any one of the wires is broken, the odometer won't move.

I'll check and report my findings...thank you for your input

RonW wrote:

landspeed wrote:So if an odometer was turning at say 7/10 speed, all of a sudden, what do you suppose that could be.

A broken gear. Odometergears.com to the rescue, of course.

That was my first guess. Thanks.

Mine doesn't work at all in spite of the new odo gears Rich proffered with my new E28.....

Troubleshooting time.

Is the procedure to start with the sensor in the diff and work forward?

I love how these cars ('80s BMWs in general) are so easy to troubleshoot. I had a surge at part throttle that is now almost completely gone due to cleaning all the underhood contacts with Deoxit and finding a few vacuum leaks.

If your speedo works, don't bother with the diff sender. Look at what RonW posted above.

I know this is probably a dead thread, but i wanted to help out anyone who may be having the same problem. It turns out that the problem was not in the electronics, but instead in one of the reduction gears in the speedo. Since my odo was working (albeit fast) and all the gears looked good upon cursory inspection, i overlooked the underside of one of the gears. It turns out the orange colored gear is really a two part gear and has a much smaller reduction gear attached to its underside. This tiny reduction gear was all chewed up because the orange gear and the white gear (which turns the odo) had become fused together, due to the gears deteriorating themselves and sticking to the shaft. I replaced this orange gear with a un-chewed one, cleaned the pilot shaft it spins on, and viola! It works perfectly!!!

A thread with a definite answer to an unusual problem like this one is NEVER dead! Thanks for the update!