Speedometer broken - it reads 20mph above actual speed! Any ideas?

byrne_baby_byrn

Hi guys,

Here's the problem with my speedo - any ideas thoroughly welcomed...

When the car is powered off the speedo needle rests at zero. When you turn the ignition to "power on" the needle jumps to around the 15-20mph mark. Then when you start the car, the speed stays around 15mph above the speed. At higher speeds, it could be 20-25mph above the speed.

Don't want to put ideas into people's heads but I rang a garage and asked them about it. One guy reckoned that that problem can occur when a car is being jump-started: if the two cars are connected with jumper cables and the jumping car turns on their ignition it can mess up the speedo of the car being jumped! They didn't say how to fix it, only that they don't fix that kind of problem.

Anyway, if anyone can be any help I'd really appreciate it. Don't particularly want to get ripped off by a garage (who does?) if it can be sorted out easily.

Thanks guys,

Jason

Anan1

Ring Hamiltons in Dublin 8, 01-4755157. (I'm starting to feel like a mobile advertisment for the place!). They are that rare thing, a competent & reasonable auto electricians.

crosstownk

I'll have to second the Hamiltons recommendation.

byrne_baby_byrn

Thanks guys. I'm not based near Dublin but if I can't get any joy soon enough I might as well give them a shout.

In the meantime, if anyone has an idea what might be wrong with the speedo, let me know... it's driving me nuts!!!

Seth Brundle

For reference, when looking for help on a problem, try and include details of the car (model, year, etc.).
Was your car jump started? By whom?
It could be a number of things from a speedo cable or sensor to the ECU bein knackered.

byrne_baby_byrn

kbannon wrote:

For reference, when looking for help on a problem, try and include details of the car (model, year, etc.).
Was your car jump started? By whom?
It could be a number of things from a speedo cable or sensor to the ECU bein knackered.

ECU being knackered? Don't like the sound of that. The car is a 98 Citroen Xsara. Yes, the battery was a bit wonky for a week or so, so the car was jumped a couple of times. It's entirely possible that someone did actually turn on their car while the two cars were connected with jumper cables.

Any ideas on how to narrow down the problem?

JHMEG

You could try disconnect the vehicle speed sensor and see if the problem persists. You'll probably get a Check Engine light on if you do, but it should go away when you reconnect the VSS.

byrne_baby_byrn

JHMEG wrote:

You could try disconnect the vehicle speed sensor and see if the problem persists. You'll probably get a Check Engine light on if you do, but it should go away when you reconnect the VSS.

That's what I like JHMEG, a debug plan Any idea where the VSS would be on a Citroen Xsara?

JHMEG

Sorry, Citroen is not my speciality!

VSS is usually on the gearbox, but so are other connectors. Google may help you.

Did you disconnect your battery (for like 30 secs) to reset the ECU since the problem started? I would do that first just to be sure to be sure.

kikel

Call it a safety feature. You'll never be going quick enough to have a crash. if you obey the limits. Also you won't get done for speeding:D

byrne_baby_byrn

JHMEG wrote:

Did you disconnect your battery (for like 30 secs) to reset the ECU since the problem started? I would do that first just to be sure to be sure.

I changed the battery since so it would have been disconnected for a bit. I might try it again just to be sure though. I'll let you know how I get on - thanks.

Google's my next stop for a quick tinker with the VSS. I'm presuming that if I diconnect the VSS and the needle drops then it's a faulty sensor; if the needle still stays above 0mph then it's something else. Am I correct in that?

byrne_baby_byrn

kikel wrote:

Call it a safety feature. You'll never be going quick enough to have a crash. if you obey the limits. Also you won't get done for speeding:D

Ha ha, you're spot on there. It doesn't really bother me but, unfortunately, the NCT is looming so I need to get it sorted before I drop it in. I presume that a wonky speedo is a failure.

Seth Brundle

Im not sure if the seedo accuracy would be part of the test as most speedos are not accurate.

The NCT manual (from www.ncts.ie) gives the following as reasons for failure:
(1) Missing or not working.
(2) Cannot be seen from driver’s seat.
(3) Lighting of Speedometer Not working.

Yours works - just not accurately, but show me one that is accurate!

byrne_baby_byrn

kbannon wrote:

Im not sure if the seedo accuracy would be part of the test as most speedos are not accurate.

The NCT manual (from www.ncts.ie) gives the following as reasons for failure:
(1) Missing or not working.
(2) Cannot be seen from driver’s seat.
(3) Lighting of Speedometer Not working.

Yours works - just not accurately, but show me one that is accurate!

Thanks kbannon, that's an interesting point. If I can't get it fixed soon I'll just have to put it through and see what they say. I have to admit it does feel pretty macho seeing the speedo needle flash past 100mph when you're doing 75 on the motorway

JHMEG

byrne_baby_byrn wrote:

Google's my next stop for a quick tinker with the VSS. I'm presuming that if I diconnect the VSS and the needle drops then it's a faulty sensor; if the needle still stays above 0mph then it's something else. Am I correct in that?

That would be the idea, yes.

I would also check the condition of the connectors and wiring to the VSS. Rust/moisture can cause strange things to happen too.

byrne_baby_byrn

JHMEG wrote:

That would be the idea, yes.

I would also check the condition of the connectors and wiring to the VSS. Rust/moisture can cause strange things to happen too.

Coolio, I'll give it a bash tomorrow and I'll let you know how I get on with it. Thanks again

bloodyheartz

Hi,

I would like to know if you have been ablw to solve this problem. I am actually having the same problem here. Please help

colm_mcm

This thread is 7 years old, please start a new topic stating the make/model and symptoms,