ABS activating at low speeds, no ABS light - Volvo V70 1998

[joadahle]

Hi, first post on this site.
I recently had my 98 V70 at the norwegian MOT, and one of the faults it came back with was "ABS activates at low speed". This has been a problem almost since I got the car 4 years ago, but has managed to go through the MOT regardless untill now.

The symptoms my car express is that; when driving at low speed, very often the ABS activates. When this happenes, no ABS or Tracs lights illuminate. There are no lights when driving normal either, only a "service"-light that goes off around 1-2 minutes after starting the car.

Something I remember noticing, a bit after I got the car, was the speed dial almost jumping, before it finally stopped working all together on my way back from a roadtrip. When the fault first arrived years ago, I read online it might be the module itself, so I did as suggested and re-soldered the contacts in it. Problem was still present after repairing it.

Fast foreward to today, I am still trying to figure out what the problem might be. Ive now gone through many posts and suggestions on what might cause the problem:

-Ive replaced every sensor with new ones, as well as the ring the sensors look at.

-Ive tested the wireing from the module-plug to each and every component that it was wires to (sensors showed the expected ohms, and no wire was really above 0.5 ohms), in acordance with the haynes wireing diagram.

-Ive swapped to two different part number ABS modules. One for a 1999 v70 (which wasnt compatible at all), and one for a 1998 without TRACS. Funny part here is that the one without TRACS and the one that was installed when I got it (which had TRACS) works the same. The problem is till present regardless of wether it had TRACS module or not. On the same topic, I am not sure if my car has TRACS or not, as the "Tracs Off" light doesnt illuminate at startup, nor when I press the Tracs button on the dashboard.

-Ive read faultcodes for why the "service" light illuminates. It comes back with CI-221 "VSS Signal- Signal Missing" (no ABS faults). But CI means Combined Instruments, even though Ive replaced the sensors which gave me the speedo back (the speed is indicated on the instrument panel). I can also see the speed each sensor sense, as well as the output speed from the ABS and the indicated speed on the instruments on my OBD2 scanner (all seems to match). And Ive tried clearing the CI fault, but it comes back and ABS still act up at low speeds.

I will add that my plan is to inspect the Instrument Cluster for any fault as far as I can do with the equipment I got. Also, I do not have money for putting the car through a mechanic for them to fix unless it is absolutely nessesary.

At this point Im very close to giving up, even tough I want this car to still be on the road. But what can I do? Any suggestions?

[matthew1]

Welcome to MVS, Joadahle.

When you say ABS activates, what do you mean exactly? There is an ABS system check at low speed after start.

[misha]

That service light is just an oil change (service time) reminder.

[abscate]

It is usually the tone rings that cause intermittent abs. The other thing to check is that the driveshaft nut is tight. If the shaft moves a bit , it will trigger ABS
If you have a TRACS switch in the dash , you have tracs. If you don’t, you might not have tracs

Options in NOR are different than USA so have to be careful with these statements

[joadahle]

Thanks for all the replies untill now.

First I'll add that I found out the previous owner had removed the bulbs for both the ABS and TRACS lights, so no wonder why they didnt light up (I also previously confused the ABS lighting up on startup with a different light). They now finally actually light up (I took two unsued bulbs to replace them), however the ABS still activate when im going low speed, and still without illuminating the lights.

To answer matthew1 :
When I slow down, like arriving at an stop or a red light, the ABS activate in the way that I can hear the oump working and feel the brake pedal shake. Like mentioned earlier, no lights illuminate when this happenes. According to my OBD2 tool all sensors see the actual speed im doing.

Misha :
May well be, but I didnt think these cars had that. Didnt say anything on my OBD2 about it when I plugged it in, but the service light has been out since I fisrt clicked "clear faults".

abscate :
The rings them selves are basically brand new, front changed two months ago, and rear changed last year. Same with sensors. The nut on the driveshafts has been torqued to the spesifications my Haynes manual says to do, first some NM, then 60 degrees more. This had been done a few times as Ive been changing other parts in there as well, and it doesnt feel loose. Also as mentioned, the sensors still sense the speed im going as I can see their output in the OBD2.
And on tracs, I have it. The bulbs was just removed by the previous owner, so no wonder why I couldt see them light up.

[misha]

Service light is a service(oil change) reminder and it says SERVICE.
It turns itself off after a few minutes after starting the car .
Yes...these cars have it.
There is a separate submenu on Volvo diagnostic tool for clearing service light.

Clearing engine codes or codes from other modules in the car doesn't clear service light!

If you meant on check engine light(lambda light for EU cars) it's engine management fault light and it have nothing in common with service light.

[joadahle]

May well be. However, it hasn't lit up since I first connected the OBD2, so I guess it doesn't really matter. Unless the CI-221 code could trigger it?
Also no, the lambda light doesn't light up after starting the car.

I'm wondering what else I could do to fix my ABS. I could cheese my way through by disconnecting something like the pump or something, but I'd like to get it fixed. But I feel like all the signs point to the module not being faulty, at the same time all rings and sensors have been replaced, and all wiring has been measured.
The weird thing I'll add on is that when I plug the OBD2 in to look at the ABS system while driving, the car has yet to activate at low speeds, while when I plug it out, it starts activating again.

[aeg]

Misha knows what he's talking about. CI codes don't turn on any lights. The service light comes on purely based on mileage and time. It turned off because you cleared it with your scanner.

When you have the scanner plugged in, is the ABS light flashing? This means it's in diagnostic mode and the ABS is disabled...

[joadahle]

Yes. Now that I have the bulbs fixed and they actually illuminate, yes it flashes when the OBD2 is diagnosing it.
I feel like that may point back to the module itself, so tomorrow I will pull it out as its my last day of it being road legal until I get it fixed, and see if I should resolder the common fault-points.

Any other ideas is welcome