ABS help please

[Joe]

Having a few problems with my car at the moment.

About a month ago I had front discs and pads replaced and the wheel bearing on the near side front which comes as a whole unit including the hub. Everything has been working fine, then at the beginning of the week I started to get a juddering through the brake pedal like the abs was trying to cut in whenever the brake was applied. The abs and traction control fault lights had also lit up on the dashboard. Took it to my local mechanic who run a diagnostic on it and it came up with a fault on the abs/speed sensor. Got this replaced and cleared the faults, drove out the garage and got about half a mile down the road and the lights came on again with the same juddering on the pedal. Spoke to the mechanic again and he suggested another hub in case this one was faulty.

Also noticed that my mpg is down to 26mpg!!!

Anyone experienced anything like this?

(The car is an 05 GT by the way)

[alexperkins]

check the wiring to the speed sensor - they can sometimes rub through and fail

[88rsr]

probably a sticky caliper somewhere (check all 4 wheels by jacking up and spinning... without handbrake on the rear, they should spin fairly free) if one is sticking it will decrease your mpg and be trying to lock the wheel up even if the brakes are applied lightly which will cause the abs to kick in, (and the traction control in turn as they are a linked system)

just an easy and more importantly FREE check which you can do yourself (use a proper trolley jack though not the widowmaker scissor jack that comes with the car)

[CharlesK]

probably a sticky caliper somewhere (check all 4 wheels by jacking up and spinning... without handbrake on the rear, they should spin fairly free) if one is sticking it will decrease your mpg and be trying to lock the wheel up even if the brakes are applied lightly which will cause the abs to kick in, (and the traction control in turn as they are a linked system)

just an easy and more importantly FREE check which you can do yourself (use a proper trolley jack though not the widowmaker scissor jack that comes with the car)

Yeah I'd agree with that, seems to make most sense!

[david burton]

check the wiring to the speed sensor - they can sometimes rub through and fail

Good call, I think Joe was reporting 1/2 mileage too so the speed sensor would cause this. Where do they rub through?

[alexperkins]

They sometimes become unclipped from their holders at the base of the suspension and rub on tyre/rim near the top of the arch

[david burton]

cheers - do you know if there is any way to test the sensor? resistance, voltage etc?

[alexperkins]

Its difficult due to the rotor design - unless you have a really good multimeter set to resistance then its hard to measure. Connect to each respective wire, and rotate the wheel slowly. Resitance should go up and down

Best way to test is vagcom though! In ABS controller then Measuring Blocks

[Joe]

Thanks for your replies everyone, didn't really think about the wire going to the abs sensor. Suppose this could be the most likely cause for this.

[david burton]

It was the hub in the end (just for info)