406 Speedo, Rev counter and Fuel gauge erratic

I’ve had a problem with the Speedo in my 406 for a few weeks now,
hopefully going to get time to sort it out shortly by replacing the
sender unit and transducer.

However, a couple of times over the last week or two my rev counter
dropped to zero a few times. Seemed to do it at exactly the same time
as the speedo.

Yesterday however was the scary one. The speedo, rev counter and fuel
gauge kept flickering, occasionally dropping down to zero and
’wiggling’ around the correct reading. The engine note didn’t seem to
be affected. Also, the temperature gauge seemed to be ok. This
happened for about 10 minutes, and the speedo gave up shortly after.

This has worried me a great deal. Is there something else that could
be amiss here? I don’t want to have to change the sender
unit/transducer only to find it’s something completely unrelated. I’m
thinking if it’s happening to all three (albeit separately), maybe the
sender unit is ok?

 

I have the same problem with my 406, often it will go up in increments of
10mph.
Love to know the cure.

Andy

 

I get the "wiggle" on my 205 speedo as well, it just randomly
bounces around going around 5-10mph either side of the actual speed.
It’s just not annoying enough to pay to get it fixed so I would love
to hear a cure as well :wink:

 

Hi

A 406 speedo is totally different to a 205 one.

406s use an electronic sensor on the gearbox to work the speedo, Theres no
mechanical linkage between the two parts.

A 205 will have a mechanical cable to drive its speedo, The cable wears out
& you get the needle wiggling.

I would check the earth screw on the pcb on the back of the instrument
assembly, A common fault is the screw is normally lose & this gives you a
dodgy earth connection.

 

Cheers, will have a look next time I build up the patience to
dismantle my dashboard.

 

So I take it the thing to do with the 406 is clean up the sensor and it's
contacts and wiring first of all......
I thought that it took a speed trigger from the alternator?

Andy

 

The speedo on the 406 is electric, fed by a small sender unit which on mine
(RHD '97 1.9 TD) is located on top of the gearbox, just where the passenger
side driveshaft enters. 6mm hex bolt holds it in.

If the feed plug has 3 connections, it's about £28 to replace - if only 2
connections, then it could cost £85!!