V70 - Intermittent ABS 'Brake Failure' warning.

shrav_reddy · Post by **shrav_reddy** » 04 Jun 2010, 12:29

Hi guys, I have a very strange problem with my 2005 V70 and any help would be greatly appreciated.

When the fuel tank drops below half, the ABS brake warning symbol lights up (and the ABS does not work). When I fill up the car with diesel, the warning lights disappear (and ABS works perfectly) until the fuel gauge registers about half full again.

This problem has been present for over 6 months. I took it to a Volvo specialist, but they did not know what the problem was. Do you have any ideas?

C@lvin · Post by **C@lvin** » 04 Jun 2010, 14:20

OK,that's one I've never heard of but here is a wild guess. You might have a bare wire in the wiring to your rear wheel speed sensors and when the suspension adjusts to the weight of the full tank (loweing the body relative to the wheels) it is pushing the wire against something and shorting it out. Are you getting any codes when the ABS light comes on?

You can try to visually examine the wiring or you could test for this possibility by measuring the continuity on the rear speed sensor pins at the ABS module connector under the hood. If resistance is infinite when the tank is full and normal with half or less then that would be pretty decisive. I had to uninstall my VADIS and haven't reinstalled it on my new computer so unfortunately I can't give you the pin-outs for the connector or provide the expected resistance. Maybe someone else could look it up for you.

Good luck!

shrav_reddy · Post by **shrav_reddy** » 08 Jun 2010, 02:48

Hi C@lvin, I'm not particularly technically competent, so i cannot answer your question. However, if your hypotheses is correct, then with a 3/4 full tank and car load of people, one would expect the ABS warning lights to come on, right?

This doesn't happen in practice.

Cheers, Shravan.

Post by **vjaneczko** » 08 Jun 2010, 10:44

Does your V70 have load-leveling?

When the ABS stops working, does it stop working while you drive or is the light illuminated once the car is started?

Did the specialist clean off the ABS sensors and magnets (they tend to get filthy)? You might want to pull the tires and look for wire rubbing and any ABS filth.

shrav_reddy · Post by **shrav_reddy** » 09 Jun 2010, 02:16

Hi, I'm not sure if my V70 has load-levelling. Is it standard on a regular car?

The ABS warning light lights up when the tank is about half-full. This happens as I am driving. I can confirm that the when the ABS warning light is lit, the ABS does not work and when ABS light is unlit, the ABS works fine.

I'll get my mechanic to clean the ABS sensors and magnets and look for any wire rubbing.

Thanks for your help.

All the best, Shravan.