OBD2 on early 850s

[ShadeTek]

Hi Chris, the weather here is Baltic to say the least and not having a garage, I am not going to be found next year frozen to my suspension . The ABS tends to give problems more in warmer weather anyhow so it's not a huge problem just now, but it would be excellent to get it sorted out once and for all. I'll need a new battery before that as I have the interior lights dimming syndrome when turning over in the morning. Going up north for Christmas so I think I will try and get that before I go. I'll also try to keep some voltage in the system at battery changeover to avoid getting rough idle during the engine ECU learning cycle.

I'm currently downloading a V70R performance video on Bit Torrent just now. Dunno what it involves but sounds like some kind of racing stunt. I'll post here when it's complete.

[img]http://homepages.nildram.co.uk/~marsheil/DTC/absdtc.jpg[img]

Cheers

Tek.

[Chris_Rogers]

Yes too cold to muck about with it now unless you have to. The poor battery may have some thing to do with it as well.
I'm sure you're aware of the problems with the ECU, but this usually starts with a right rear sensor problem.
I'll see if I can find a wiring diagram for you if you care to e-mail me.
Good luck.

[ShadeTek]

Hi & thanks for the offer, I have PDF diagrams of a LHD version I got from e-bay. It contains lots of other info too. We can swap data if you want. I can leave it on my ftp server for you to d/l at your leisure. I don't know about the rear sensor problem....what was that about?

Cheers

Tek.

[ShadeTek]

I'm sure you've all seen this picture somewhere before on the net. But it's been snowing here, it's Christmas , so what the hell. The funny thing is the website I got this from, has gone to the bother of blanking out the number plate. It's still visible on the reflection from the bonnet of the tailing car. Doh!

[img]http://homepages.nildram.co.uk/~marsheil/V70.jpg[img]

Happy Christmas

Tek.

[Chris_Rogers]

When the ABS ECU fails the first circuit to go internally is usually for the right rear sensor, this is followed by others.
This leads people to replace the rear sensors, which can only be done as a pair. They then find that the ECU has to be replaced anyway, this doubles the cost and bother of the problem.

[cootuk]

Do the wheel sensors ever need cleaning?
If I got the front left fault (so probably not the AMS module) then I'd first try cleaning the sensors and doublechecking the wiring....i guess it depends how often the code is popping up and whether the ABS light is staying on.

[ShadeTek]

I've been told by a Volvo specialist that the sensors do need cleaned. I cleaned my rear sensors which were caked in gunk. This can cause problems, also incorrect tyre pressure can cause problems I'm told!*? My codes tend to come up in warmer weather as I said, so it may be more sensor/electronic related, but I can narrow that down by swapping the sensor over.

Hi,
The problems sounds like the famous Volvo 850 ABS Cableproblem.
The cables from the sensors are crimped under the fuse box, those crimps are not good, every now and then the signal is to low, specially in slow speed, in this case the ABS kicks in.
There is two ways to solve it.
1) Remove the fusebox, re-crimp the cables.
2) Buy the extended cable kit from Volvo and replace the cables from the weels sensors to the ABS unit, the old cables are cut by the ABS box, and the new are connected to the ABS unit.
I know that Volvo did offer the replacement for free up to 50000 KM.
/Freddie

[ShadeTek]

Hi Freddie. When you say the ABS sensors are crimped uner the fuse box, is the signal path from the sensors passing under the fuse box and being extended by extension wiring, or are the ABS sensors connected to the fuse box itself? Can you elaborate please.

They are extended from the fusebox to the ABS Unit.
God nows why, there are no fuses binding the sensors and the ABS Unit, as far as I know.
I have not manage to unfold the fuse box (I am a fraid I will break it), so I think I am going for the cable switch..

If you go to your local Volvo dealer/service shop, they have Tech document regarding this matter..

Regards,
Freddie