964 speedo not working

[ian c2]

any ideas where to start looking ??

[dilbert]

I think you have a speed sensor in the gearbox, on the nearside above and to the left of the driveshaft/cv joint. Perhaps it's on the other side, I forget. Anyhow, check the wiring, pull the sensor out and have a look at it. Equally check that the plug hasnt come out the back of the speedo.

If you want to pull the guages out of the dash, I recommend that you start with one of the smaller ones, as they're a bit easier to get out. Certainly the clock, you can get at the back from the trunk. When trying to get the guages out, go to halfords, and get some silicone lubricant. Make sure you get the little tube otherwise it will go everywhere. Leave the lubricant to penetrate for a minute or so. You cant really have too much of the stuff.

Using a screwdriver, tease back the rubber grommet, and squirt the libricant between the guage, and the grommet. Do this at at least three places around the periphery of each guage.

Once you have one guage out, the rest are easy, because you can reach through the hole left by the gauge, and push the one next to it out from behind. Try not to damage the dash or the guage.

Failing all of that, you'll have to do some electrical tests.

Edited by dilbert on Thursday 19th June 16:14

[ian c2]

plug on gearbox looks ok , as does plug behind speedo .

its a 6-speed btw .

what can i check now ??

thanks
ian

[Ultra Violent]

There is a relay in the fuse box that if broken will stop the speedo working. I forget which one it is.

[dilbert]

ian c2 said:

plug on gearbox looks ok , as does plug behind speedo .

its a 6-speed btw .

what can i check now ??

thanks
ian

Hmm, I'm more used to a G50 5sp.

Err, I don't know. If it's all looking O.K. it's not a mechanical fault, like plugs or damage.Much more likely to be electrical.

I think I'd start by buzzing out the connections, since that's the last of the mechanical stuff to check, and closest to the electronics. It's a bit painful though. I don't know the exact details of the link, but I do know roughly how it works, on the earlier Carrera.

Basically the speedo provides a high impedance input/output (both) which sits at a nominal voltage, but can be shorted to ground by the speed sensor. That input/output also goes to the cruise control module, if there is one. The basic idea, is that as the rotor in the gearbox passes the sensor, the switch in the gearbox is activated. The faster the drive shaft goes the faster the switch switches (on and off).

When the sensor is closed, the speedo monitoring point goes to zero and when open to the nominal voltage, back and forth (square wave). The rate of switching is determined by your speed. The cruise control and speedo use these fluctuations to establish how fast you're moving.

The best, but most difficult test is to connect an oscilloscope, to the sensor wires, and spin the wheels to see if the square waves are there. An easier test is to use an AC coupled averaging multimeter to measure the RMS voltage of the square wave. You should see the voltage increase with speed.

I think the best bet is probably to disconnect the battery, speedo, cruise module, and sensor. Then temporarily connect the two wires at the speedo end, and just measure continuity of the whole loop at the sensor end. If you get continuity, it tells you the wiring is OK.

Then remove the temporary connection, reconnect the battery and speedo but not the cruise module, or sensor. With the ignition on, see if you can measure the nominal voltage.

Then connect the sensor, but leave out the cruis module. Go for a drive and test the speedo without the cruise module, a fault on that could cause the speedo not to work.

Then get a new sensor.

Then get a new speedo!

HTH.

It might be the case that on later models, the ECU is in between the speedo, and the sensor. That would tend to suggest that the sensor is o.k. because the ECU is still working. Perhaps though, it would then be worth looking at the diagnostic port if you have one.

Edited by dilbert on Thursday 19th June 17:31

[ian c2]

sounds like its going back to ninemeister ...... it was working before i took it there to have a BIG battery drain fixed . i figured it was a little job that i could easily fix myself .

[dilbert]

ian c2 said:

sounds like its going back to ninemeister ...... it was working before i took it there to have a BIG battery drain fixed . i figured it was a little job that i could easily fix myself .

Well, if they broke it, get them to fix it! (sounds like you might have some other latent problem though)

Edited by dilbert on Thursday 19th June 17:40

[Ultra Violent]

I was physically present when 9m nicked the relay I was talking about from one car to fix another. So i'd check the relay before you start ripping the rest of your car apart.

[ian c2]

lol

checked the lid to see if there was a fuse or relay listed , but nothing there !!!

i know they ended up with my fusebox apart , so may be something and nothing .

[ian c2]

was the car you are talking about equipped with cruise or obc ??

[Ultra Violent]

One car was a 3.6 964 turbo, the other was a 964 3.3 turbo. Neither had cruise.

[ian c2]

fanx !!!

i think youre talking about the silver turbo ??

now i just need to find out which one it is !!!

[CraigyB]

These people repair 964 speedos

http://www.speedycables.com/

[ian c2]

thanks craig .
but i doubt it is the actual speedo .

9m had my car for about 4 weeks and had it in pieces serching for a 9amp drain !!!

i think its something other than speedo or box

[dilbert]

ian c2 said:

thanks craig .
but i doubt it is the actual speedo .

9m had my car for about 4 weeks and had it in pieces serching for a 9amp drain !!!

i think its something other than speedo or box

Blimming eck!

I should think they were able to find that, by following the smoke trail!

Edited by dilbert on Thursday 19th June 18:47

[ian c2]

lol
i dont mind workin on cars in my down-time , so had a go at it myself for a few days .... in the end i phoned robin for advice and his exact words where "fkin' hell !! i'm surprized its not on fire "

this kinda panicked me .

so as i was due in france for another month , i just dropped the car off for them to take there time with ....

they solved the problem , just this little problems now here

[robh964]

Ian

Is the spoiler working?

If not, you may have a loose connection under the drivers seat (RHD), mine stopped working when I was p1ssing around putting new seats in, a quick fiddle and it worked again

Rob

[ian c2]

fixed spoiler .

but ...... when i got the car back my electric seat controlo wasnt working on drivers side !!!

one of the little jobs i did today . i didnt pull the seat though , i fumbled around like a virgin tryna get a bra off , 5 mins later it was fixed !!!

maybe they left something else unplugged under there ??

will look first thing in the morning ,

thanks

[ian c2]

btw ,
no way am i slating 9m for this .

my instructions where for them to do as much as they could to build the car back up before i got back in uk , if they ran out of time all i needed was the drivers seat bolted in so i could drive it home !!

as i said , i like to work on my car in my down-time , and if i can fix this simply without getting them involved i would prefer it this way .

every problem solved helps me understand my car a little better !!!

[ian c2]

another old topic ....

i will be looking at this again today and tommorow as i would like to know how fast i am driving .

from what i can gather , 91 and later cars use an abs sensor for the speedo input .

things to look for are a faulty sensor or wiring (should light up on dash) faulty relay , or blown abs fuse .

i'll let you know how i get on ....