The cold killed my Speedo and RPM

[BennyM]

My 525i had been sitting outside for about 2 days with temperatures gradually decreasing until tonight when it reached -7 and I hopped in the car to head home. Apart from feeling quite stiff, everything worked fine except for the speedo and RPM gauges. The RPM said I was idling(just after cold start mind you) at about 300rpm, while the speedo never rose above 10 once I started driving. When they moved, they did so very sluggishly. Eventually, while on the freeway at somewhere around 70, the RPM needle showed 1000rpm and the speedo registered -5mph.

I estimated 70mph based by setting the MAX SPEED alarm to 70 and accelerating till it chimed. I surmised that the MAX SPEED indicator was actuallyy accurate by testing different speeds alarms and observing my speed in relation to the traffic around me. I compared both observations to my knowledge of how people generally drive on that stretch. I also based my speed on the seat-of-my-pants feel and my visual perception of velocity.

So, why would the MAX SPEED alarm work, but the RPM and speed gauges not? And, all the above considered, what is broken? All other gauges and indicators seem to work properly. The archives didn't seem to have much info related to this particular malfunction.

Would appreciate your thoughts guys.
Thanks,
Ben

[shogun]

click here for info (http://www.bmwe34.net/e34main/maintenance/electrical/capacitors.htm)

[BennyM]

Ok, so I know this could be one of those capacitor issues, but I figured that if such were the case then other parts of the instrument cluster would also malfunction. I went back out and did the instrument lamp test. After holding the check control and turning ignition to position 2, the BMW computer info displayed on the check control screen, but nothing else happened. Then, after a couple seconds, I heard a clunk from the engine bay (I think) and all the lights all illuminated and the needles on the instruments all went up as originally expected. The clunk sounded kinda like a large relay had switched somewhere ahead of the firewall. Also, at the point that I heard this clunk and the instruments came on, the brake pump(or whatever that is that hums before starting the engine) turned off. Now, I wonder if this has to do with the instrument voltage regulator (mentioned in the archives) or simply a very cold battery? If it were the battery, I assume a half hour drive on the freeway would charge it enough to answer that theory. Right? Please let me know what you all make of this.

Thanks,
BennyM

[shogun]

Battery could also be an issue.

So better check the easy things first before you dig into the dashboard.
Maybe you open the hood and remove the fuse box cover, let someone set the ignition to 2 and then listen from where the noise comes.

Could be also just a stuck relay.

Find a digital multimeter and stick the probe into the cigarette lighter socket in the center console.

The following are the detail figures I use for my own evaluation:
With key out of ignition switch, should see 12.4V or above. 12.0 V is getting low.
With key inserted and turned to position 2 (don't start car), should see 12.0V or more. 11.6V would be too low.
Crank car, catch the lowest voltage reading during that couple of seconds. Should see 10.0V or above. 9.5V would be marginal.
The above just consider the health of battery itself.
Car running at 1500 RPM or more, should see 13.7 to 14.3V, 13.6V or below means the charging system is weak.

[BennyM]

last night the car sat in an actual garage, keeping the temp slightly above zero (-17 outside the garage). I don't know if it was that I turned the engine on while the instrument test had the needles maxed or not (it was a hunch), but now the gauges function normally. This car does have a tendency to self-heal. Wow, it's nice to know how fast you're going.

P.S. Sometime this week will mark the cars 200,000 mi birthday. How should I celebrate? Oil change? Brake fluid flush? I think I'll throw in a new brake switch and a wash too.....that is, if it gets warm enough for the car washes to open again.

Thanks again.

[JonE]

Benny,
Give it the "works" carwash when it warms up here tomorrow to about 20degrees!
Jon

[shogun]

If you have such cases of electronic probs and find out that the battery is not the case: sometimes just a reset helps. Just drain all the power out of the whole system, also from the electronics.

Reset procedure is on my page. Sometimes works like a miracle.

[BennyM]

Benny,
Give it the "works" carwash when it warms up here tomorrow to about 20degrees!
Jon :p

[JonE]

"get it washed in the snow, right? Think I'll wait till Friday :)"

By then it'll just be another dirty car with over 200K! ;) With my luck it would sleet or snow on Saturday, just after washin' it up