1984 635CSi Tach & Temp not working

[anthonym]

Hello All,

I am new here. I have a 1984 Euro 635CSi that the Tach and Temp Needle do not work. My Haynes manual is useless.

When I ground the smaller terminal in trhe temp sensor, the high temp light comes on. When I ground the larger terminal the needle does not move. When the ignition is off the needle rest far left. When on it rises to the low temp mark. Any thoughts on diagnosing this?

Anthony
Seattle, WA

[KC Ron Carter]

Both are connected to the SI, Service Interval.

If the SI is not resetable that means the SI batteries are dead.

If the SI batteries are dead the systems can send the signal through the wrong wire and you get no signal.





SI reset and batteries

With the ignition switch at (position two) and the engine not running, grounding pin seven #7 of the diagnostic connector to pin one #1 for approximately three (3) seconds will reset the oil service lights. Grounding pin seven #7 to pin one #1 for approximately twelve (12) seconds will do an inspection service reset.

More information.

http://www.specialistcarsbmw.co.uk/stevenage/service/service_lights.htm


http://www.unofficialbmw.com/images/reset1.gif


1. Ground
4. Temperature sensor
7. Reset
8. TDC sensor yellow
9. TDC sensor shield
10.TDC sensor black
11.Start signal
12.Alternator charging excitation voltage
13.Ignition coil
14.Alternator charging supply current
15.Oxygen Heater

It will signal an oil change need between 5k and 7k depending on your indicated speed since the last reset. It will signal stealer inspections at all the predesignated miles.



http://www.eskimo.com/~dalus/bmw/e36/electrical/e36_reset_service_lights.html




SI Board Swap Out

Last but not least - the SI Board. Above is a new SI Board with lithium batteries and below is the old one. Note the blown battery on the old SI Board (green circle). The light blue rectangle shows the actual service indicator LED's which appear on your dash display. These LED's are mounted on a separate circuit board which must be pulled out of the old SI Board and plugged into the new one. This is an easy task. The purple arrow shows the orientation of the SI Board relative to the driver.


If it fails to reset then you need batteries.

Varta battery 500RST OE part.

Radio Shack: part number 23-191: $6.49 for set of two; they come w/solder tabs on them.

1.2 volts / 700mAh

Charge fully B4 installation on SI board.

Consider mounting batteries "remotely" under dash, etc. in separate holder for easy removal in future (i.e. not pulling the console out and apart); you can buy a plastic holder at RS. Run leadwires from holder to SI board connections. Makes life easy if you ever need to replace batteries again.

From Radio Shack, get:
1) You'll need a twin AA battery holder ($3)
2) 2 AA NiCAD rechargeable batteries ($6)

Later,

[anthonym]

Thanks for the reply! Good information.

I was able to reset the service interval LED lights. Do you think the problem lies within the board itself?

Anthony

[KC Ron Carter]

to see if the SI keeps the reset or loses it.

If it loses the reset you need to replace the batteries.

Later,

[anthonym]

Just so I am clear on this, if the Service Interval reset reverts back to its pre-reset state, the batteries on the SI board are bad and should be replaced and the Tach and Temp gauge not working might be a result of the bad SI batteries. If the Service Interval lights remain in a working state (For how long?), there is something else at issue. Correct?

Anthony

[KC Ron Carter]

If the reset is retained the batteries are good and then you need to look for a different correction.

But I get at least on fix a month on the batteries.

Later,

[anthonym]

Originally Posted by KC Ron Carter

If the reset is retained the batteries are good and then you need to look for a different correction.

But I get at least on fix a month on the batteries.

Later,

Ron,

I took the instrument cluster off and it is the updated board already! Get this, I reset the blue connector (#2) and all is well. Go figure. Thanks for all of your help.

Anthony

[mike454]

I have a 85 M6 with a badly corroded battery on it,it has actually got some of the circuit board under the battery corroded also.
my question is where can a person get a new board for one of these?
is there an aftermarket company that makes a lithium replacement?
thanks

[jeffreyb4me]

S.I. board battery replacement is RARELY a cure for the problems related to them. replacements are available in the aftermarket.