hi chaps.
just wondered if u have any ideas abiut my 02 sporting, the abs light is on and the speedo dos'nt work, i'm told the 2 may be related but i'm not sure, anyway someone said something about a speed sensor being the prob but apparentely theres more than 1,
any ideas please?

If the ABS system doesn't know the diff is turning it doesn't know when the wheels are stopped.

Sort out the speedo sensor first, that may resolve the ABS issue, unless an ABS sensor has gone down too.

Cheers

SPD

I thought the ABS speed sensor was separate to the speedo sensor?

Sort the speedo first, that's a safety and licencing issue and a car isn't road-worthy without a working speedo.

If it sorts the ABS then all the better. If not, you know they're not connected!

hi.
thanks for the help, ive had it on a computer thingy and it said something about an abs speed sensor being at fault tho it did'nt say which 1, the guy who did it made the speedo work from the computer while the car was stationary, does that mean the speedo is ok then or what?

When I was researching ECU connections, I recall that the vehicle speed sensor comes from the gearbox except for cars with ABS, in which case it comes from the ABS system. So, fix the ABS and I reckon the speedo will be fixed as well.

The diagnostic test to operate the speedo means the gauge is OK. It's the ABS sensor(s) you need to be looking at.

I understand that a VAG-COM interface (the "tenner and a laptop" reader) can interrogate the ABS control unit if you connect pin 7 to pin 1 but haven't tried it (I don't have ABS).

red

grandedale said:

hi.
thanks for the help, ive had it on a computer thingy and it said something about an abs speed sensor being at fault tho it did'nt say which 1, the guy who did it made the speedo work from the computer while the car was stationary, does that mean the speedo is ok then or what?

Click to expand...

Getting the speedo to work via the computer is called an output test. All it does is show that the speedo dial itself works, not that it's getting a signal from the speed sender.

The speed sender is mounted on top the the gearbox at the very back (Above the diff.) If you've not had a working speedo since a clutch change, they may've left it unplugged. (Whoever swapped it.)

The ABS light is most likely a sensor. ABS computers don't read from the speed sender; they read from the ABS sensors on the wheel hubs, and they read individual wheel speed. Diff speed is no use to an ABS computer, as it doesn't tell it what's happening with each wheel. An open diff (As found in your car.) will allow one wheel to remain stationary, while the other spins.

If it's got ABS, it doesn't have a speedo sensor on the gearbox. Vehicle speed is averaged-out from the 4 wheel speed sensors (or sometimes just the rears) and sent from the ABS ECU to the Cluster via CAN. Fix the ABS problem and you'll fix the speedo.

Your diagnostic man should be able to monitor the readings from the sensors to determine which is faulty, if not they may need to be individually scoped-out to find the issue.

Each wheel has an ABS sensor. Each sensor connects to the ABS control unit via a pair of wires.

The ABS control unit is not on the CAN-bus. The signals go to the body computer first.

The ABS control unit has the following connections to the body computer:

Pin 11 to body computer C16 - K-line for diagnostics
Pin 21 to body computer C6 - serial line for comms
Pin 22 to body computer C7 - speedometer signal

The body computer works the speedo (and also the ABS warning lamp) via a CAN-bus link to the instrument panel.

I don't know which or how many wheel signals the ABS uses to generate the speedo signal but as you can see, ABS and speedo are definitely linked so it still points to an ABS sensor fault.

red

Damaged ABS ring or Faulty sensor would be my guess, or the wiring to and from . .

of course finding the right wheel is gunna be fun
Trigg~