Speedo Sender Unit

Thu Nov 10, 2011 12:40 pm

Gentlemen,

Please help!

Non-working speedometer (a typical issue I know....) motionless when tapping on the dash. My auto electrician has tested voltage at the wire going into the differential and he has current...it is a complete circut. Having had the cluster out today, he did not see any obvious signs of corrosion/cracked solder...

He has suggested a faulty sender unit on the differential. Is this a common fault on a 1989 318i? Is this a part which can only be sourced (expensively?) through BMW? It has worked once (in my year of ownership) at the end of a very long drive....could it be a fault in the speedometer head unit?

Thanks chaps

ADJ

Thu Nov 10, 2011 1:16 pm

It is possible that it is the cable right next to the sender.

I don't think the senders fail that often, but I think they are only around £15 or so.

You have checked the fuse is OK?

Thu Nov 10, 2011 1:25 pm

I cant say that I have checked the fuse, but I would have hoped that the auto electrician would have done that today! As it has worked intermittently (twice in a year)...id be surprised if it were the fuse....but il have a play later today.

How would you go about changing the sender unit?

Thu Nov 10, 2011 1:51 pm

alexdejonghe wrote:
How would you go about changing the sender unit?

Unbolt the old one and bolt a new one in!

Two 10mm bolts hold the sender unit to the back of the diff,before wires breaking up became fashonable,the first port of call was always a new sender.

Thu Nov 10, 2011 2:10 pm

daimlerman wrote:
alexdejonghe wrote:
How would you go about changing the sender unit?
Unbolt the old one and bolt a new one in!

Two 10mm bolts hold the sender unit to the back of the diff,before wires breaking up became fashonable,the first port of call was always a new sender.

Ha! Fashionable yes....in that case rusty sills/scuttle/footwells, destroyed seat bases, spongy clutches, shagged suspension, mouldy rubber seals and whiny differentials must make us all very, very cool....

Thu Nov 10, 2011 2:21 pm

alexdejonghe wrote:
daimlerman wrote:
alexdejonghe wrote:
How would you go about changing the sender unit?
Unbolt the old one and bolt a new one in!

Two 10mm bolts hold the sender unit to the back of the diff,before wires breaking up became fashonable,the first port of call was always a new sender.
Ha! Fashionable yes....in that case rusty sills/scuttle/footwells, destroyed seat bases, spongy clutches, shagged suspension, mouldy rubber seals and whiny differentials must make us all very, very cool....

You have got the idea!

My dad was running E30's at less than 5 years old,failed speedo was always the sensor,but these days it seems to be the wire that gets the blame.

Thu Nov 10, 2011 10:04 pm

If he's an auto electrician worthy of the title, ask him to test the sensor. It's just a reed switch operated by a segmented steel disc.

Sun Nov 20, 2011 2:15 pm

well....wasn't the speedo sensor! I bolted on the shiny new £17 sensor unit and....nothing. Having said that, after I had spent ten mins under the car fiddling...it did spring into life briefly, andf then died...

The auto-electrician (see first post) said he had voltage ("a complete circut") when testing the wire coming out the differentail sensor....does this mean that internally broken wires are DEFINATELY not to blame? I'd rather not make myself look a tit by ignoring his advice and asking him to replace the wire & plug if possible!

....is it time to replace the instrument cluster?

1989 318i.

Sun Nov 20, 2011 2:26 pm

Before doing anything else check fuse (pretty sure its 11). Mine had exactly the same problem and I replaced the sender and also had an auto electrican check everything (well at least he said he did and it cost me £120).

Turned out to be butchered wiring for the CD headunit which was cauing fuse 11 to blow which is linked into the wiring for the cluster. If you have the same problem as me the MPG guage will probably wont intermitantly also.

It was BrianMoore that help me identify this one in the end.

Sun Nov 20, 2011 2:54 pm

Woah...£120?! Sorry to hear about that! All E30 owners in 2011 have to deal with hangovers of idiots ruining these cars!

....yeah I got on the case with the fuses. Pretty sure its Fuse 12 you're referring to my friend...and it was definately fully functional, and (since Ive had the car) there hasn't been an issue with the stereo really.....

My speedo (rarely) does spring into life, which makes me doubt an issue with the fuses....

IF it was a problem with the cluster (and the wire is not coroded and the sendor unit in working order), would the MPG dial also be non-functional?

Sun Nov 20, 2011 7:56 pm

MPG gauge won't read sensibly without a road speed signal, but will swing from side to side.
Fuse 11 is fuel pump. Fuse 12 is relevant to the instruments.
Chances are that the wire near the diff. is the problem, and any "auto electrician" worthy of the name should have found this, and tested the diff. sensor while the plug was out.

Sun Nov 20, 2011 8:23 pm

How frequently are the clocks/soldering points to blame for a faulty speedo on old E30's? Il change the wire and plug thanks Brian!

Bit confused how he was getting voltage on this wire and said he had a 'complete' circut, but I guess the connection broke when I drove!

Sun Nov 20, 2011 8:30 pm

If he tested for this 'complete circuit' with the diff. plug disconnected, there's a good chance that the broken ends were touching while the measurements were made. These things need to be tested without disturbing anything anywhere near were the fault is suspected to be.
Broken wire is by far the most common speedo fault, but cracked soldering faults aren't exactly uncommon either. These usually respond to tapping the dashboard.

Sun Nov 20, 2011 8:46 pm

Cheers Brian....at least both scenarios aren't massively expensive to repair....il give the differential wire & plug a bash first! The fact that the speedo pops into life sometimes when the dash illuminsates (also an intermittent fault) makes me suggest dodgy cluster connections...but il snip and solder thats wire first!

Cheers Brian

Alex

Sun Nov 20, 2011 8:59 pm

Speedo input (8 and 12) and illumination (23 and 24) are both on the white socket to the cluster.
Could be that some muppet in the past couldn't work out how to disconnect the plug, and has damaged the circuit board where this socket is soldered in.