limp mode home

[four2zerohero]

Hey guys I have questions about voltage readings. My 09/85 E23 735i auto went into limp home mode and I heard that one of the many things that can cause that is low voltage ( I think I heard sth like below 9v the tcm shuts off).
Well I checked the voltage at the battery with the car running and it read 22+volts. The voltage diddnt change much with car off after driving a while.
I also checked volts at the alternator itself and it was also above 22 (you could actually hear the idle increase a bit as you came close to the + terminal on the alternator with the red probe).
The alternator is probably a year old, I gave my original bosch one for a remanuf duralast one (perhaps not the best choice).
I know that voltage is high enough to fry a trans relay or maybe even the tcm itself.

My questions are :
1 do I need a new voltage regulator? If so, should the replacement one work with the duralast alternator?

2 is there a way to bypass a trans relay?

3 do you think the high voltage is the cause of my trans problems?

Thank you

[RonW]

22 volts is so wrong that I would have to see it to believe it. No offense intended, but I've known a few people who didn't really understand electricity or how to use a multimeter. Some of these people have even posted on this forum.

If that reading is accurate, do not start your car. 22V would destroy automotive electronics in short order. I would think your battery is ready to explode.

The fact that the idle changes just from bringing a probe near a terminal suggests a floating connection, probably in the voltage regulator.

I bet the Duralast is simply a remanufactured Bosch. Or at least a Bosch with a new coat of silver paint. If the old voltage regulator doesn't fit, it's the wrong alternator. The VR comes out with two screws. On my E28 535i, the VR can be replaced in just a couple of minutes, so it should be easy to compare the old with the new.

[four2zerohero]

Hey Ron thanx for your fast response.
I am a little familiar with electronics but not with using a multimiter so I think I'm setting the dial wrong. I'll post some pictures tomorrow so you can see what I'm doing,but hopefully im the one that's wrong.

So does the floating connection at the regulator means it has to be replaced?

Thanx

[mechacode]

Yikes. 22v would either have, or be close to, a popped fuse.

[Mark 88/M5 Houston]

Yikes. 22v would either have, or be close to, a popped fuse.

A fuse "blows" due to an over current condition; not an over voltage condition in most all cases.

[four2zerohero]

Okay so I checked again today and messed with the meter and I got around 10v at the battery with motor off and around 13.6 at idle. I guess before I had the dial set at the wrong V on the multimiter and that's why it was displaying 22.

The 13 od volts displayed diddnt change much at idle with the use of highbeams, alpine stereo, wipers etc. Did increase a bit when reved but did not rev to 2000 to see how high volts went.

The reading at the alternator was the same as the battery 13.5- 13.6 at idle and 10 not runnung . This time the noticeable idle change was not present.

Once you kill the motor volts at the battery quickly start to drop to aronud 10v as the electric cooling fan stays on.

Do you think the constant quick dips in voltage couldve fried my tcm or relay? Should the voltage at the battery stay at 12.5 not running??

thanks in advance.[/img]

[RonW]

13.6V at idle is good. 10V when off is bad. It should be between 12V and 13V. It sounds like you have a bad battery.

[four2zerohero]

It ended up being the connector at the transmission it was hangin on by a cunthair.
was able to get it back on and now i have all 4 of my glorious forward gears.

thanks to all for their useful replies

[LA]

Must have been a blond cunthair...you could have simply replaced it with the thicker red cunthair and probably been fine. No ofense to anyone intended.