For the past couple of weeks the Focus (2000 1.8 LX petrol with 174,000 miles) has had an occasional (once every few trips) fault whereby the speedometer will drop to zero (all other guages and the odometer remain functional however) and the car will lose acceleration, accompanied by a slight loss in radio sound.

When it is in one of these "episodes" it is still driveable however if you disengage the clutch to come to a stop et cetera, the engine will attempt to idle for less than a second then cut out. Fortunately the only time this scenario has happened was when approaching a roundabout, and coming to a complete stop was not necessary so simply letting the clutch out restarted the engine.

Usually the speedometer will stay at zero for 30-50 seconds and once it picks up again the engine will get a resurgence of power and the radio will regain its full sound.

I am almost certain this is the speed sensor on the gearbox (despite reading that when that is at fault the odo blanks out - which isn't happening) and it will need replaced, probably by a mechanic rather than myself, but will the problem get worse quickly (if at all)?

Secondly, if it isn't the above, what could it be?

Thanks.

The odo doesnt blank out the car will stall the speedo and revs will drop to zero but the odo doesnt tend to blank out

I had the same issue and it was the speed sensor, and my odo only blanked out a few times randomly not every time!

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Thanks guys - that has confirmed it for me that it is the speed sensor.

Once I get my next pay cheque I will buy a new sensor off eBay and either have a go at doing it myself (highly unlikely!) or get the local garage to do it.

Definitely the speedo sensor (VSS).

The speedo bottoming out and rough running/loss of power are classic symptoms, once the sensor packs up totally you may notice the odometer stops reading and just shows a fixed mileage.

The radio changing volume is because the radio has a setting whereby a signal from the VSS triggers it to increase volume to overcome road noise at speed.

Ford call it Automatic Volume Control (AVC) and the settings can be accessed via the radio menu if you need to switch it off until thye VSS is replaced (just set AVC to 0).

You can get a VSS and a new pin (essential as the old one will be mangled on removal) off ebay for about £20, you can fit it yourself in about 30 minutes but can be a mare to remove as the pin can/will snap and the sensor is always very tight.

http://www.ebay.co.uk/itm/FORD-FOCUS-SPEED-SPEEDO-SENSOR-1998-2004-TOP-QUALITY-1087548-NEW-SS1-/150731145659?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item231846c1bb

Definitely the speedo sensor (VSS).

The speedo bottoming out and rough running/loss of power are classic symptoms, once the sensor packs up totally you may notice the odometer stops reading and just shows a fixed mileage.

The radio changing volume is because the radio has a setting whereby a signal from the VSS triggers it to increase volume to overcome road noise at speed.

Ford call it Automatic Volume Control (AVC) and the settings can be accessed via the radio menu if you need to switch it off until thye VSS is replaced (just set AVC to 0).

You can get a VSS and a new pin (essential as the old one will be mangled on removal) off ebay for about £20, you can fit it yourself in about 30 minutes but can be a mare to remove as the pin can/will snap and the sensor is always very tight.

http://www.ebay.co.uk/itm/FORD-FOCUS-SPEED-SPEEDO-SENSOR-1998-2004-TOP-QUALITY-1087548-NEW-SS1-/150731145659?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item231846c1bb

I had no idea the radio had such a feature!! You really do learn something every day.

Being that the extent of my vehicle repair history is doing an oil change, do you reckon I could competently change the sensor without messing it up?