Getting to the bottom of a few issues. 940s b200

[Laird Scooby]

Originally Posted by Kingfisher8

Ok, finally got some time on the 940 tonight.

The FI ecu is 6 842 289

Im still trying g to get the the bottom of the abs light. I have the dash out and trying to check all connections are OK.
The abs bulb is connected to pin 8 & 9 from the left on the blue connector. Guess is back to tracing wires in the car.

Thanks

The ECU number is short a few digits, it should start 0 280 so it's probably 0 280 842 289, i'll have a look and see if i can cross-reference that.

Had a look then realised that's the Volvo part number you've found, equates to Bosch 0 280 000 949

https://www.ebay.co.uk/itm/304016961312

That's for a 240 but the same ECU was used in the 940 and i believe 740 models too. It's fitted to cars with the B200F engine.

The ABS bulb should have one side connected to the ignition +ve input on the cluster that comes in behind the speedo and the other side to the plug. Also on the PCB there should be a diode (although on later ABS2E probably not needed) to link it to the charge warning light for self-test purposes.

[Laird Scooby]

Originally Posted by Kingfisher8

Ok, I'm really confused now. I really hope someone can point me in the right direction or maybe show I'm not going insane...

I've followed the abs wires on the printed circuit on the dash. The wires lead to pins 8&9 on the blue connector. So dash seems fine.
Thought I would check wires from the plug for power etc. There's no pin 8 in the plug, nothing at all. No trace. Does this mean I shouldn't have an abs light?

See my reply above!

[Kingfisher8]

Originally Posted by Laird Scooby

See my reply above!

Thanks for that,

So no connection from the + behind the speedo. Blue&red to the abs bulb means broken circuit on the dash somewhere? Can I solder a wire from another point?
There seems to be a diode that has a common from some other bulbs too.

[Laird Scooby]

Originally Posted by Kingfisher8

Thanks for that,

So no connection from the + behind the speedo. Blue&red to the abs bulb means broken circuit on the dash somewhere? Can I solder a wire from another point?
There seems to be a diode that has a common from some other bulbs too.

That sounds horribly like someone has had problems with the ABS and jerry rigged a warning light to get through the MoT and disconneted the original warning light.

In basic terms, all the warning lights in the dash (except indicators and full beam) have an ignition witched +ve feed coming from the speedo connections onto the PCB on the back of the cluster.
With all the warning lights getting a common +ve feed, that means they are all earth switched. Handbrake warning light switch takes a wire to earth when the handbrake is lifted, oil pressure switch takes the wire to earth via the oil pressure switch, charge warning light takes the bulb to earth via the alternator rotor circuit. Once the engine is running, it gets a 12V +ve feed on the rotor from within the alternator so the charge warning light has +12V on both sides and goes out.

There should be several diodes connected each to the -ve/earthy side of several warning light bulbs with their banded end connected togetheron the -ve side of the charge warning light. That means all of those bulbs will light when the alternator isn't charging and as you have the early ABS (despite being a 1993 car) the ABS light should be linked by a diode to the charge warning light.

Most of the warning light bulbs are ~0.6W but the charge warning light usually needs to be 2.2-3.0W roughly. By linking half a dozen or so 0.6W bulbs through diodes not only do they achieve the same current flow into the alternator rotor but a self-test function of the warning lights. Clever, eh?

Back to your problem, can you get a photo of the ABS warning light with these two wires attached to it? Also a photo of the back of the instrument cluster in the area of the ABS warning light would be helpful.

[Kingfisher8]

Originally Posted by Laird Scooby

That sounds horribly like someone has had problems with the ABS and jerry rigged a warning light to get through the MoT and disconneted the original warning light.

In basic terms, all the warning lights in the dash (except indicators and full beam) have an ignition witched +ve feed coming from the speedo connections onto the PCB on the back of the cluster.
With all the warning lights getting a common +ve feed, that means they are all earth switched. Handbrake warning light switch takes a wire to earth when the handbrake is lifted, oil pressure switch takes the wire to earth via the oil pressure switch, charge warning light takes the bulb to earth via the alternator rotor circuit. Once the engine is running, it gets a 12V +ve feed on the rotor from within the alternator so the charge warning light has +12V on both sides and goes out.

There should be several diodes connected each to the -ve/earthy side of several warning light bulbs with their banded end connected togetheron the -ve side of the charge warning light. That means all of those bulbs will light when the alternator isn't charging and as you have the early ABS (despite being a 1993 car) the ABS light should be linked by a diode to the charge warning light.

Most of the warning light bulbs are ~0.6W but the charge warning light usually needs to be 2.2-3.0W roughly. By linking half a dozen or so 0.6W bulbs through diodes not only do they achieve the same current flow into the alternator rotor but a self-test function of the warning lights. Clever, eh?

Back to your problem, can you get a photo of the ABS warning light with these two wires attached to it? Also a photo of the back of the instrument cluster in the area of the ABS warning light would be helpful.

Sorry I think I didn't explain myself properly.


The abs light isn't getting any power from the + that comes in from behind the speedo.
So I'm assuming there is a break in the pcb from there to the light.
I was just wondering if there was a way of just soldering a wire from one point to another to give the abs light power? And if so wheres best to go from?

[Laird Scooby]

Originally Posted by Kingfisher8

Sorry I think I didn't explain myself properly.


The abs light isn't getting any power from the + that comes in from behind the speedo.
So I'm assuming there is a break in the pcb from there to the light.
I was just wondering if there was a way of just soldering a wire from one point to another to give the abs light power? And if so wheres best to go from?

Do the warning lights either side of the ABS lamp work? If so, identify the +ve feed to them and run a short link wire across to the +ve side of the ABS lamp. Chances are it's a dry solder joint though.

To fix that you'll need a low wattage soldering iron (~25-30W, preferably temperature controlled), a solder-sucker, some new 60/40 tin/lead solder and a steady hand. Find the dry joint and heat with the iron, adding a little fresh solder. Once flowing, use the solder-sucker to remove all the solder then add fresh to resolder the joint.

You might be as well going through all the joints on the PCB and repairing any and all that look dry, you might just find the ABS light works after that without any further intervention.

[Kingfisher8]

I know its been a while, bit I finally got some time on the 940. Removed speedo again pulled off some of the pcb and found a crack in the wire feeding the abs light and temp light, so I ended up soldering a link wire in. Abs light works and goes out now. Not tried driving yet to see if it re appears when driving to indicate a faulty rear speedo sensor.

But.. I now have an srs light permanently on? Wasn't on before and can't remember if it used to come on and off in the key on check . Any ideas?

[Kingfisher8]

Oh, I've also gained what looks like something for the cat, over heat maybe? Its not in my book but is 3rd from the left. This comes on on self check but then goes off.
I never had the srs light on before. For some reason I also can't check the codes for it under the bonnet on pin 5.

And my speedo still don't work. As the abs light only comes on with the self check and remains off while driving can I assume the speedo sensor is ok and its likely the speedo itself?

[Laird Scooby]

Originally Posted by Kingfisher8

I know its been a while, bit I finally got some time on the 940. Removed speedo again pulled off some of the pcb and found a crack in the wire feeding the abs light and temp light, so I ended up soldering a link wire in. Abs light works and goes out now. Not tried driving yet to see if it re appears when driving to indicate a faulty rear speedo sensor.

But.. I now have an srs light permanently on? Wasn't on before and can't remember if it used to come on and off in the key on check . Any ideas?

Have you got an airbag?

[Kingfisher8]

Originally Posted by Laird Scooby

Have you got an airbag?

Um... I dunno tbh I just presumed i did because of the light. Will it say airbag on the steering wheel?

I do have pin 5 on the diagnostics under the bonnet but no codes or anything when I plug into it.