Car is a 2003 Octavia VRS, 120k on clocks

Today I opened the bonnet and discovered my drive belt appears to be disintegrating - black dust all over the screenwash bottle etc. Looking at the belt from above, it is not sat fully on the tensioner, and appears to be wearing down the ribs that are sat on the tensioner. Its a 3 week old belt as I had noticed the same on the old one, and thought it was from when my aircon pump siezed, but now thinking about it, the wear it on the wrong side of the belt. I think its the tensioner seizing, but not 100%. Does anything else run on that side of the belt to check?

I also have the following issues:

Speedo is not working - I have changed the speed sensor on the gearbox, with no success. It could be wiring, or could be the clocks themselves. Is there any way of testing if the wiring is broken? I have ran the car using VCDS Lite and get no speedo readings. I know I can send the clocks away to be scanned, but would like to confirm it is them at fault before I shell out (£50 for a check inc postage, £150 if need repairing, all via BBA Reman). VCDS Lite brings up EML and code 18805 I think - speedo inop.

Also, car is stuttering at low revs on occasion - still boosting to 0.5/0.7 bar (changes from drive to drive) so wondered if I have a boost leak causing the stuttering. Any way to check?

Edited 5 April, 201313 yr by broken biscuit

Do you have a single or double V belt?

If you have a/c, then that and the tensioner use one side and everything else uses the other.

Make sure that your reversing lights are working. The roadspeed sensor shares a fuse/feed with the reversing light switch.

Its a double V belt. All fine on the 'inside' which goes round the two bottom pulleys and the a/c pump, It's the side which runs against the tensioner which is worn - my tensioner is smooth, with no grooves, and the belt is riding half off it, wearing down.

With regard to the speedo - the reverse lights are fine, all fuses fine. I have checked the sensor, and it is getting 12v and a ground to the sensor. The only wire I dont know if i can test is the pulse wire (output) from sensor to ecu/dash, as I dont know where it goes to, to test it. I have a horrible feeling I have a broken wire somewhere under the battery, as I lost a/c last year due to a broken wire which cost me two hrs of an autoelectrician to diagnose and fix. If i can find out where the output wire terminates, I can put some volts down it, and check if I get them at the sensor, ruling out any breaks in the wire. If its not a wire fault, its the clocks. I dont like to be beaten, and dont like to pay anyone if I can fix it myself.

RWBaldwin - I think you helped me last year with the aircon wiring problems. Bloody car.

The reverse side of the belt should also contact the a/c pulley so that the belt is between the tensioner and a/c pulley. If it's on the other side, the a/c compressor is running backwards!!

It should look like this

The white/blue wire from the roadspeed sender goes to pin 3 of the black 14-pin connector in the connection box where it becomes a green wire to pin 28 of the blue dash connector.

The belt looks like that. Its fitted correctly, must be the tensioner.

When I remember where the 14 pin connector is, I will run some wiring checks. I think its under the battery? Where is the dash connector? Back of the clocks? I want to eliminate the wiring before I buy any new parts or send the clocks away

There is a connection box underneath the windscreen wiper motor. The lid is about 125mm square. On the the back of the dash panel insert there is a green and a blue connector.

Tensioner issue fixed. Edge of the pulley had cracked off. This was shredding the belt. One tensioner replaced, problem solved. Tomorrow I have dedicated to checking the wiring over from speedo sensor to dash to determine one way or the other if I have a wiring fault (which I will then fix) or a cluster fault ( at which point i will shout, cry and then send the clocks to BBA Reman for checks / repairs (£150 or so inc courier)).

I have checked the wiring as per RBaldwins description - there is no break in the wire between the speedo sensor on the gearbox and the cluster. I have also swapped the sensor with one in a mate's golf gti (same part) and still its the same. I cannot see any alternative other than to send the clocks away to be checked, unless anyone can suggest anything else? I really cant do with the car off the road for 3-5 days, but will if no alterative.

I have checked the wiring as per RBaldwins description - there is no break in the wire between the speedo sensor on the gearbox and the cluster. I have also swapped the sensor with one in a mate's golf gti (same part) and still its the same. I cannot see any alternative other than to send the clocks away to be checked, unless anyone can suggest anything else? I really cant do with the car off the road for 3-5 days, but will if no alterative.

It's rare, but it is possible that the drive wheel in the gearbox is broken.

Without a breakout box, I would release the terminal 28 at the cluster. Connect the voltmeter between this terminal and ground. Roll the car slowly and the meter should alternate between 12V and zero.

It's rare, but it is possible that the drive wheel in the gearbox is broken.

Without a breakout box, I would release the terminal 28 at the cluster. Connect the voltmeter between this terminal and ground. Roll the car slowly and the meter should alternate between 12V and zero.

Is this done with the engine running? Or (forgive my ignorance) will the engine not run with the cluster removed?

Is this done with the engine running? Or (forgive my ignorance) will the engine not run with the cluster removed?

With the ignition on and out of gear.

You're providing the power to move the car - not the engine  

Best find a handy mate to have a play at the weekend. For now, the wife is driving it, with the strict instruction to keep away from policemen and speed cameras, and to drive like her mum!