Dispatch 98/99 Speedo Inop/erratic

[frenchenstein]

My "S" reg Dispatch 1.9TDi speedo is erratic and sometimes doesn't work, it may read 30mph sometimes then jump down to zero and then read 10mph, wierd! the odo and trip 'seem' to be working, is this a common fault? any info appreciated - Paul

[kfk]

If the speedo needle isnt moving but the odometer continues to clock up the miles you can be certain the fault is with the speedo head.

 

If the needle and odometer stop moving the signal comes from the gearbox speed sensor:

 

1, the speed sensor is electrically faulty

2, the speedo drive to the sensor isnt isnt turning due to the gear having failed on the differential within the gearbox

3, the geared wheel to the speedo drive from rhe differential isnt driving the sensor

4, electrical failure between speedo drive & speedo head

[frenchenstein]

If the speedo needle isnt moving but the odometer continues to clock up the miles you can be certain the fault is with the speedo head.

 

If the needle and odometer stop moving the signal comes from the gearbox speed sensor:

 

1, the speed sensor is electrically faulty

2, the speedo drive to the sensor isnt isnt turning due to the gear having failed on the differential within the gearbox

3, the geared wheel to the speedo drive from rhe differential isnt driving the sensor

4, electrical failure between speedo drive & speedo head

 

 

Thanks for that, it would then appear to be the head, I'll try and source a second hand one, will it need to be recognised by the cars' brain via a diagnostic plug in or is it a straight forward plug in and go?