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Hello All, wonder if anyone can please help with the below:

My speedo goes up to the maximum 155 mph, and shows this speed no matter what speed i'm doing, the MPG gauge is also showing the incorrect reading (does not really move), when i brake the speedometer goes back down to zero, when i accelerate the needle shoots all the way up to the end of the dial. As this is not the wheel sensor as previously thought (according to a mechanic who did a quick inspection following changing one of my rear wheel bearings), any ideas what the hell this could be? The guy at the garage reckons its electrical so nothing he can help with, so far no ones seems to have a clue!! Luckily I have the sat nav to show the speed i'm doing so i can still drive..

The rev counter and all other dispays on the dash are fine, no error codes..

Any thoughts?

Also, if i disconnect the battery for a short period will this help??

I have a E46, 318, 2000 year model. Many thanks.
 

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Yeesh, never heard of this, perhaps a short circuit somewhere? E46's are they cable driven or electronic?

Tom
 

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Hello All, wonder if anyone can please help with the below:

My speedo goes up to the maximum 155 mph, and shows this speed no matter what speed i'm doing, the MPG gauge is also showing the incorrect reading (does not really move), when i brake the speedometer goes back down to zero, when i accelerate the needle shoots all the way up to the end of the dial. As this is not the wheel sensor as previously thought (according to a mechanic who did a quick inspection following changing one of my rear wheel bearings), any ideas what the hell this could be? The guy at the garage reckons its electrical so nothing he can help with, so far no ones seems to have a clue!! Luckily I have the sat nav to show the speed i'm doing so i can still drive..

The rev counter and all other dispays on the dash are fine, no error codes..

Any thoughts?

Also, if i disconnect the battery for a short period will this help??

I have a E46, 318, 2000 year model. Many thanks.

Hi, I edited your post title to add your car info as per posting rules.


Who said there was no error codes out of interest? have you had them read recently?

If the wheel speed sensors have ALL been checked out as being ok....

The vehicle then obtains its speed from a sensor on the differential. The vehicle speed sensor is located on the back cover (aluminum) of the differential, next to the fill and drain plugs.

I would check and replace that as a first port of call...
 

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Discussion Starter #5
Thanks all for your kind help, in answer to your query yes it is a manual, sorry forgot to mention this. I think I will try a BMW specialist to re-check the sensors on the wheels and will update this post with the outcome. The only thing to add when the speedo started going wrong, my car was frosted up as it was out in the snow, dont know if this would be a possible cause but thought i'd mention anyway.

Thanks again.
 

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If you can get a video you can post it on youtube or a similar hosting site and then embed it here, this will give a clue to your problem.

Tom
 

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Speedo is operated from the N/S/R/ wheel speed sensor.

What side was the wheel bearing done on? And did it do it after it was fitted?

Also like you mentioned get the codes read at a good BMW specialists, ABS codes and Instrument(Kombi) codes
 

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Discussion Starter #9
Hi, the bearings went on o/s rear wheel a week or 2 before the speedo went funny. Could it still be the speed sensor at fault even though I have no DTC warning light on? I have booked in the car for a diagnostics check next week which should hopefully pinpoint the problem. I will also try disconnecting the battery for a while to see if this has any affect (however unlikely!).

Am i right in presuming there are 2 speed sensors, one on each rear wheel, the one on the transmission is actually for measuring revs? So as my rev counter is operating normally, i can rule this out as being the problem, or am i completely wrong?

Thanks again all.
 

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Hi, the bearings went on o/s rear wheel a week or 2 before the speedo went funny. Could it still be the speed sensor at fault even though I have no DTC warning light on? I have booked in the car for a diagnostics check next week which should hopefully pinpoint the problem. I will also try disconnecting the battery for a while to see if this has any affect (however unlikely!).

Am i right in presuming there are 2 speed sensors, one on each rear wheel, the one on the transmission is actually for measuring revs? So as my rev counter is operating normally, i can rule this out as being the problem, or am i completely wrong?

Thanks again all.
I thought there was a speed sensor on one front wheel and one rear at the opposite side..??

No, you cant rule the DIFFERENTIAL sensor out at all. it works in tandem with the speed sensors as far as I am aware.

There is no transmissions sensor on the manual gearbox



edit// It seems no one on Bimmerfest knows either :lol
 

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Not sure about the E46, but on the E36, the diff sensor (as Boostist mentions) wiring can rub on the diff as it looms towards the front of the car.The wires can bare and short and give problems with the speedo.

Like I say I don't know if it's the same on an E46
 

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I thought there was a speed sensor on one front wheel and one rear at the opposite side..??

No, you cant rule the DIFFERENTIAL sensor out at all. it works in tandem with the speed sensors as far as I am aware.

There is no transmissions sensor on the manual gearbox



edit// It seems no one on Bimmerfest knows either :lol
No sensor on the diff on a e46 :thumbsup

Also there are wheel speed sensors on ALL four wheels, they serve the ABS/Traction control. The sensors you are thinking of are the brake pads sensors, One O/S/R and the other N/S/F.

The wheel speed sensor on the N/S/R as well as doing the ABS/Traction control also does the vehicle speed for the cluster.

And regarding the rev counter BM-Boy-2000, that is done by the Crankshaft position sensor :)
 

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Discussion Starter #13
I noticed on the motorway when it was dark my headlights appeared dim, however i had a garage do a free battery test and they said it was fine. This problem of mine is getting more and more bizaare. The car is booked in for a diagnostics check and they said they will check the wheel sensors, i just hope its all not too pricey :( Thanks for your help all. I will update this post with the outcome.
 

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Discussion Starter #16
Thanks to all who responded, the problem was rectifyed simply by removing the instrument cluster and replacing the same one back in, for some reason it worked! although im hoping the problem does not return, also the speed sensors etc all are functioning correctly, the battery/charge/alternator was also all fine in the end so that was not the problem either. Cheers all.
 
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