help what is going on with my brakes

[stixman77]

i have a xc70 98-s awd with 106k
when i am driving normally and move my foot from accelerator to brake pedal most times there is a flash of a warning light on the dash it only comes on for a split second and is gone and it flashes red so i believe it is a serious warning.
the picture is like a lightbulb with lines shooting out as if it were lit, this happens most times when im driving normally however... occasionally when i go to brake the pedal seems to vibrate and wont depress right away and i can only feel it in the pedal and not really the wheels although when this happens i usually s(edited) myself a bit and im not really sure if the wheels are vibrating as well, i have had cars in the past that developed warped discs which very noticably was felt in the wheels and other than the shuddering sensation braking was normal, whereas my problem here feels very different and seems to be coming from somewhere near the drivers footwell and also when this happens ive noticed the vibration makes a kind of whirring sound but rough like a pump or a motor thats failing maybe? and also seems to be coming from the footwell area
please help i cannot find any information anywhere that would explain this problem but seems to me like it should be something simple

[850tech]

Not sure about the light, but the pedal issue sounds very much like unwanted ABS engagement, though warped rotors cause similar symptoms but without the pump motor sounds.

[BEJinFbk]

I suspect you are seeing a flash of the "Bulb Failure" lamp.
Dirty contacts for your brake light lamps are often the cause.

Here's the relevant page of the OM - See Indicator #9:
http://new.volvocars.com/ownersdocs/199 ... 70_019.htm

[stixman77]

thanks for the advice and yes this is definitly the abs engaging i have checked the sensors and they seem fine do you think this is possibly the sensors at the wheels or most likely the abs unit under the bonnet
also every now and again the traction control light comes on could this be related to the same thing, when this light comes on the engine seems to go into a safer mode restricting power a little which is very annoying and the abs seems to be engaging almost every time i press the brake pedal now
in my handbook it says the 4 wheel drive models do not have traction control is this wrong

[Ozark Lee]

The Volvo traction control (TRACS) actually uses the brakes via the ABS module in a lame attempt to control traction. I don't have a 4WD version but since TRACS is worthless on the 2WD versions I can see why it was omitted on the 4WD versions.

Your problem is not typical but since you briefly get a bulb failure indicator upon braking and since the brake pedal switch is an input to the ABS module I think I would start with the pedal switch itself.

Does your ABS warning light come on when you put the key in position II?

The reason I ask is that many unscrupulous sellers will remove the lamp to mask an ABS problem or in other more benign cases the lamp has been on so long that it has burned out.

There are two kinds of ABS modules on the '96 and on Volvos, those that have failed and those that are going to fail. In most cases it comes down to cracked solder joints. There are a number of re-builders that will correct the solder joints for a reasonable fee or you can cut the module open and do it yourself if you are handy with a soldering iron.

...Lee

[thecheat]

So the Volvo has an e-diff like VW's XDS? Fancy...