Focus 1.8tdci ECU problem? Electrical problem? Engine malfunction

[isetta]

My brother's 2008 Focus mk2.5 1.8tdci.

A few days ago he is driving and car loses all power, will only tickover, throttle not doing anything.  he turns engine off and tries restart but starter motor will not work, immobiliser light flashing constantly and dash says engine malfuction.

Car is recovered to his house.

I go there with my Tunnelrat fault code reader. car exactly the same (starter motor will not work, immobiliser light flashing constantly and dash says engine malfuction.). He has two keys, both behave the same. Fault code reader won't communicate with car.   After turning ignition on and off many times and unplugging and plugging in fault code reader many times the car suddenly decides it will start and the fault code reader shows p2263 Turbo signal above max and U2023 communication network fault ABS module. These are the same fault codes that have been appearing for  months when the car did run (cleared many times and always reappeared). So don't appear to be directly related to this current problem.

So he felt he could not use car in case it does the same thing again in a dangerous place (it was quite dodgy last time).

So we are thinking there is an electrical connection problem. So we have removed the fuse box below the glovebox. Checked all connectors on it. Checked all relays and fuses are fitted properly. Opened up the fuse box to visually inspect the circuit board (BCM) in it. everything looks fine and put it all back in the car.

We checked all fuses / relays were in the engine fuse box properly. checked the big plug that goes in the top of that fusebox. all appears to be ok. There are a lot of wires that go into the bottom of that fusebox. But i can't get that fusebox out. There is a one bolt that releases it but it is kind of held down by those cable looms going into the bottom of it. So I do not know if there could be a problem with a connector there. Is there an easy way to get this out that has eluded me?

We accessed the ECU under the left front wheel arch liner. all of the three connector plugs there seem to be in good order. (four shear bolts on cover, could not shift with centre punch, no dremel tool for cutting slots in bolts - got cover off by hammering screwdriver into plastic around bolt heads to cut round each bolt.)

We checked the huge plug connector on the top of the engine towards rear where the plug and socket are hold together with 10mm bolt. looks OK inside. Other sensor plugs unplugged and checked.

Car is currently:- starter motor will not work, immobiliser light flashing constantly and dash says engine malfuction. He has two keys, both behave the same. Fault code reader won't communicate with car.  

So he is on the verge of towing it to the scrap yard, which seems such a shame.

It does seem to be like this could just be an electrical connection problem - but where? one dodgy earth? but where?  could it be it needs a new ECU? or a new BCM?  Could this be the well known fault of the soldering in the speedo console (is that just earlier cars?). I have tried the pressing the speedo console in various places.

I would love to be able to help him get this car going as he paid £850 for it last December and has no money.

So one key point here is that currently the OBD code reader won't communicate with car - does that give a clue to a certain area to focus on?

Any helpful comments gratefully received

 

 

[HighHo]

Have you checked the battery voltage? That's all I can think of as a quick test.

[Tdci-Peter]

2 hours ago, isetta said:

It does seem to be like this could just be an electrical connection problem - but where? one dodgy earth? but where?  could it be it needs a new ECU? or a new BCM?  Could this be the well known fault of the soldering in the speedo console (is that just earlier cars?). I have tried the pressing the speedo console in various places.

The combination of Immobiliser, Engine Systems Fault, and not being able to connect a diagnostic system, plus being intermittent, does sound like a bad connection in the HS-CAN bus that runs from the Cluster to the ECU. The classic 2006 problem was the CAN bus pins going dry joint where the connector socket was soldered to the Cluster PCB. But there are also 3 connectors in the CAN bus between these two modules, plus the ECU & Cluster connectors. Two are low down under the trim panel just in front of the front passenger door, (there are actually 3 connectors there, but the CAN bus goes through two), and the big connector inside the engine bay fusebox.

The resistance across a CAN bus, with the car switched off, should be 60 ohms. You can measure this between pins 6 & 14 on the diagnostic connector. If you unplug any of the connectors in the CAN bus circuit, it should rise to 120 ohms, as you will no longer have the ECU 120ohm resistor in circuit.

On a Mk2/2a, this fault is unlikely to be the BCM, it will be ECU or Cluster, or connections between them. CAN bus is the obvious starting point.

 

[isetta]

Thanks Peter, I was hoping you would reply. I had forgotten about checking the ohms (I have seen you mention this many times before). I do have a suitable multimeter.

"Two are low down under the trim panel just in front of the front passenger door". I think you mean the panel that would to the left of the passengers left foot. Will have a look there. 

"and the big connector inside the engine bay fusebox." do you mean the one in the top of the engine fuse box which is visible when taking the lid off the fusebox? There are a load of wires going into the bottom of that fusebox also that I can't seem to get to.

I do have a soldering iron and some experience of soldering (replacing failed capacitors on countless computer motherboards) so if the connectors do not show a problem I will get the speedo console out and dismantle (I have seen youtube videos on this).

Are you aware of any basic tests I can carry out on the ecu with a multimeter on various pins? Are the ECUs known to fail?  I see there are ECUs for sale on eBay but mostly without a key. But a ECU without the key (immobiliser chip in the key) is no good to anyone is it?  or am I misunderstanding.

Thanks for your advice. I will let you know of any progress but it might not be for a few days.

[Dave sport tdci]

I have had problems recently with focus Mk2 56 1.8 tdci intermittent problems with communication cam bus drop out 

Apparently the focus has common problems with the clocks soldier cracking on the Maine plug 

Re soldier the pins on the inside all fixed give them a go mine looked ok but were clearly playing up 

[Dave sport tdci]

 

 

[Tdci-Peter]

5 hours ago, isetta said:

"and the big connector inside the engine bay fusebox." do you mean the one in the top of the engine fuse box which is visible when taking the lid off the fusebox? There are a load of wires going into the bottom of that fusebox also that I can't seem to get to.

Yes, that is the beastie.

Called C90, and its pin-out is:

It carries most of the wiring for the ECU. The HS-Can bus is on pins 1 &15. This pic can be downloaded as a .PNG, when it can be seen a bit better. This pin-out is not on the circuit diagram available on this site, this is the best I have found, and seems right (in all the wires I have checked so far) for the Focus despite saying Kuga.

I can extract more pin info from the circuit diagram if needed.

I have not heard of any ECU failures on the 1.8TDCI, at least not on this site. The ECU alone would need to be programmed using Forscan for at least PATS, maybe other stuff ideally. The PATS keycodes seem to be stored in both the ECU and the Cluster, so they are often available as a pair with a key, but it is a big change to swap both, with no guarantee of success.

 

[isetta]

Thanks. If the weather’s good next bit of work on it will be Tuesday evening

[isetta]

Don't you just hate it when threads / advice does not show what the conclusion was. So here goes:

Yipee! Car is now running again. Started by doing Ohm test on OBD socket. It showed 120 (so a break somewhere). I looked at the engine fuse box connector (c90) looked OK. 

Took the trim panel off just ahead of the front passenger door. There were two big block connectors here. A larger black one and a smaller grey one below it. The black one did not seem to have canbus (grey/red and blue/red thin wires) in it. The grey one did. There was some minor corrosion in the grey one. Cleaned it up. Ohms still showing 120. (this car is a mk2.5 so maybe different to what peter describes)

back to c90 . whilst my brother watched the ohmeter i pulled c90 in and out and found that intermittently the ohms dropped to 60. I concentrated on the two pins for the canbus wires (grey/red and blue/red thin wires). they looked OK but ohms weren't steady. so what I did here was bent the two pins with thin nosed pliers into a slight curve to create more contact pressure. I also took the red plastic insert out of the bottom of the plug, then squashed the connectors a little and put red bit back in. After doing this the ohms seemed steady 60.

But after putting tools away found car failed to start again and ohms back to 120.  Now got to work on the grey connector ahead of passenger door again. Found contact intermittent here so gave those contacts same treatment as c90.

car now seems OK (optimistic but it's only just been done and not had a long test).

The contact cleaner I was using dries very quickly and leaves no residue. Would in be better if the terminals had something on them like vaseline/petroleum jelly applied sparingly?

Thanks Peter, my brother was on the verge of towing the car to the scrapyard.  

Hope it keeps going fine, at least if it plays up again we have some idea of what to twiddle with at the roadside. If these connectors cause more trouble I think bypassing them with some long lengths of wire soldered on will give more confidence that it won't keep doing it.

[isetta]

spoke too soon. played up again but got it working again by playing around with connectors.

based on the stuff above and findings it does definitely seem to be a break in the high speed canbus between the instrument cluster and the ECU under front left wing.

based on the info above the ohms on pins 6 and 14 of OBD socket should be 60 but will show 120 if a break. If I take a reading with the plug/socket disconnected in the engine fuse box &/or the plug/socket disconnected in front of the front passenger door and it shows 120 then does anyone reading this agree that it seems that the instrument cluster canbus connection seems OK, as if there was a break there then the ohms would now read infinity wouldn't they?  as if cluster fault it is not connected to the ECU end of the canbus or the instrument cluster end of the canbus.

 

So everytime it plays up, if we check the ohms and it says 120 and we then disconnect one of the aforementioned sockets and the ohms still stays at 120 (and not infinity) that rules out the fault being at the instrument cluster end of the canbus doesn't it?  does that sound right?

So leading on from that, I am thinking that perhaps I should just run new long wires direct from instrument cluster to the ecu under left front wing.(twisted like the existing 2 canbus wires - blue/red and grey/red). So my question here is, between the instrument cluster and the ECU under left front wing, do these wires connect to anything else whatsover apart from the OBD socket? so if i cut the existing two wires at the instrument cluster and cut the two wires at the ECU, and cut the two wires at the obd socket and then put new wires from instrument cluster to OBD socket and then on to the ECU then it should help.  New wires to be soldered. Does that sound good or do the wires need to connect to anything else I have overlooked?

Thoughts please. This car is too good to go to the scrapyard just because of this intermittent problem.

 

 

[Dave sport tdci]

Have you checked the clocks soldier cracking job ????????? 

[Tdci-Peter]

4 hours ago, isetta said:

So everytime it plays up, if we check the ohms and it says 120 and we then disconnect one of the aforementioned sockets and the ohms still stays at 120 (and not infinity) that rules out the fault being at the instrument cluster end of the canbus doesn't it?  does that sound right?

Yes. The diagnostic connector (DLC) is right next to the cluster, and the other plugs are between the DLC and the ECU. So the 120 ohm reading at the DLC is due the terminating resistor in the cluster, showing the connections to the cluster are ok. Be careful with intermittent readings though, they have a habit of seemingly deliberately making and breaking in such a way as to mislead you! I have been misled that way quite a few times, and only finding the truth after a lot of checking and re-checking!

When I had the faulty cluster, I got a very high reading, well up in the kohm if I recall, when I disconnected C90. That was the 2006 cracked joints on the cluster connector problem.

The HS-CAN bus, although its speed of 500kbps is very modest by current standards, does still need some care in layout. That is why it has terminating resistors at both ends, to reduce echoes and noise, and the spurs to intermediate modules are kept as short as possible.

The connection order in a 1.8TDCI is:

Cluster, DLC, C112 pins 11&12, C113 pins 17&18. Then through the bulkhead into the engine bay.

Then to the ABS/ESP module, then the EHPAS, then the brake bleed connector in the engine bay fuse box, then C90, then the ECU.

There should be 3 connectors in front of the passenger door, but one is quite a bit higher up if I recall. C112 & C113 are two of those three.

So as you can see, the ABS & EHPAS (steering) are important nodes in between the DLC and ECU. If you could locate the twisted pair of wires in the loom spur from the bulkhead grommet down to the ABS, you could put a direct link from there to the DLC. You probably would not need to cut the existing wires, having a 2nd pair in parallel with the originals would do little or no harm if it roughly followed the same route. It is only 500kBPS after all. But the ABS and EHPAS must remain as nodes in a continuous route from cluster to ECU.

Running a parallel twisted pair all the way from DLC to between C90 and the ECU might work on a good day, but when the original wiring goes open circuit, the layout then effectively has a very long spur via the EHPAS & ABS to the broken circuit. Electromagnetically that is very ugly! Likely to generate quite a lot of corrupted packets.

For anyone else reading this (?), on the 1.6TDCI & 2TDCI with the Eolys additive, the additive dosing module lies between C112 and C113. On petrol engines with belt driven steering, the EHPAS node is missed out. On keyless vehicles, the KVM lies also between C112 & C113.

 

 

[Dave sport tdci]

6 hours ago, isetta said:

spoke too soon. played up again but got it working again by playing around with connectors.

based on the stuff above and findings it does definitely seem to be a break in the high speed canbus between the instrument cluster and the ECU under front left wing.

based on the info above the ohms on pins 6 and 14 of OBD socket should be 60 but will show 120 if a break. If I take a reading with the plug/socket disconnected in the engine fuse box &/or the plug/socket disconnected in front of the front passenger door and it shows 120 then does anyone reading this agree that it seems that the instrument cluster canbus connection seems OK, as if there was a break there then the ohms would now read infinity wouldn't they?  as if cluster fault it is not connected to the ECU end of the canbus or the instrument cluster end of the canbus.

 

So everytime it plays up, if we check the ohms and it says 120 and we then disconnect one of the aforementioned sockets and the ohms still stays at 120 (and not infinity) that rules out the fault being at the instrument cluster end of the canbus doesn't it?  does that sound right?

So leading on from that, I am thinking that perhaps I should just run new long wires direct from instrument cluster to the ecu under left front wing.(twisted like the existing 2 canbus wires - blue/red and grey/red). So my question here is, between the instrument cluster and the ECU under left front wing, do these wires connect to anything else whatsover apart from the OBD socket? so if i cut the existing two wires at the instrument cluster and cut the two wires at the ECU, and cut the two wires at the obd socket and then put new wires from instrument cluster to OBD socket and then on to the ECU then it should help.  New wires to be soldered. Does that sound good or do the wires need to connect to anything else I have overlooked?

Thoughts please. This car is too good to go to the scrapyard just because of this intermittent problem.

 

 

Do you not see my post's ?

 

I have tried to help you and you just ignored my help ?

At least have the respect to respond to my efforts to try to fix your problem it really is very rude 

[isetta]

Dave Sport TDCI: I have not ignored your posts . I have considered if the cluster is at fault and have raised a query on if this can be ruled out by my findings as per my post yesterday. 

"based on the info above the ohms on pins 6 and 14 of OBD socket should be 60 but will show 120 if a break. If I take a reading with the plug/socket disconnected in the engine fuse box &/or the plug/socket disconnected in front of the front passenger door and it shows 120 then does anyone reading this agree that it seems that the instrument cluster canbus connection seems OK, as if there was a break there then the ohms would now read infinity wouldn't they?  as if cluster fault it is not connected to the ECU end of the canbus or the instrument cluster end of the canbus."

I don't want to take the cluster if my findings do indeed rule it out. 

TDCI-Peter - thanks - it seems there are more connections to the canbus wire than i thought.  On an old Cortina it was easy to visually look at where wires went. On the more modern cars the number of wires has increased exponentially and everything seems hidden. You can't just open the bonnet and see everything clearly.  I suppose the upside is we do now have cars that do almost double the mpg of Cortinas.

 

[Dave sport tdci]

50 minutes ago, isetta said:

Dave Sport TDCI. I have not ignored your posts . I have considered if the cluster is at fault and have raised a query on if this can be ruled out by my findings as per my post yesterday. 

"based on the info above the ohms on pins 6 and 14 of OBD socket should be 60 but will show 120 if a break. If I take a reading with the plug/socket disconnected in the engine fuse box &/or the plug/socket disconnected in front of the front passenger door and it shows 120 then does anyone reading this agree that it seems that the instrument cluster canbus connection seems OK, as if there was a break there then the ohms would now read infinity wouldn't they?  as if cluster fault it is not connected to the ECU end of the canbus or the instrument cluster end of the canbus."

I don't want to take the cluster if my findings do indeed rule it out. 

TDCI-Peter - thanks - it seems there are more connections to the canbus wire than i thought.

 

Look when the clusters play up they are intermittent and to the eye look ok you are checking everything and ignoring the elephant in the room the clocks they are a common problem with Mk2 mk2.5 not the ECU 

lots and lots of people have had very similar problems and resolved them very easily and quickly  having the resolder job on the back of the pins ? 

If you can soldier re do them and that will most likely fix your friends car very simple and easy job 30 minutes instead of the many hours messing around with ECU wire ?

[Tdci-Peter]

14 hours ago, Dave sport tdci said:

If you can soldier re do them and that will most likely fix your friends car very simple and easy job 30 minutes instead of the many hours messing around with ECU wire ?

I too have had the same cluster solder fault, on my 2006 Focus. It was very common for that year, I have heard of dozens of reports. But for other years it is much less common. Not unheard of, but no more common than other faults like dodgy connectors. It only takes a minute or so to check the CAN bus resistance and re-check with a plug disconnected. I did that when I had my cluster fault, and it confirmed the fault was at the cluster end.

It is not that easy to get the cluster safely out of the fascia, on my car those lugs at the top were well dug into the foam, and without previous experience it took quite a while to ease it out. I knew the transparent cover was brittle, and there was already a little crack on one edge. I also have since looked for replacement covers, and have not found any, so a broken cover is expensive and annoying.

At the moment it looks like the fault is in the other part of the CAN bus, away from the cluster, but I would not rule out anything until it is fixed, hence my little note about intermittent faults. So you could still be right, and a fault is in the cluster, but the evidence I have heard from Isetta is that the fault is elsewhere. And that is all I can go on currently.

So your posts are not being ignored, but are only one part of a process that neither you nor I can control, so please stay with us and see if this problem can be resolved. Whether in the cluster or elsewhere, I would be equally pleased to get a positive outcome.

 

[DaveT70]

It's the cluster.

Dry connection on the multi plug joints.

You won't fix the problem until you have the board re soldered

[isetta]

you are not the first person to say that. But have you read it all. As mentioned above - when the car is working the ohms on obd pins 6 &14 is 60 as it should be. When the car won't start it is 120.  That stays at 120 when I then unplug connector c90 in the engine bay fuse box. If at the time the pins in the cluster where the fault then the ohms would change to infinity. This indicates that the breakdown in the canbus is between the obd socket and the ECU, not the OBD socket and the instrument cluster.

I know intermittent faults can be tricky, but the ohms never waivers from 120 when c90 is unplugged.

I will keep you all updated.

In case anyone is reading this thread at a later date when they have a problem, it seems that the HS canbus wires run thorugh connectors c112 and c113 shown in this picture here (I know it's a Kuga pic but believe the same as Focus) as well as c90 in the engine bay fuse box. I know Peter mentions that above, but I thought I would attach this pic as C113 is not obvious when checking the car

 

 

[isetta]

for the benefit of anyone reading this thread at a later date and trying to access connector C113 on their Focus mk2.5, the way I got to it was to remove the glove box. Open the glovebox, remove the 4 screws you see along top edge. Remove the 3 screws along bottom edge (under plastic covers) and pull glove box out (you do not even need to empty it).   Reach in the hole, pull back the thick sound insulation on the left and there is c113. it pushes onto a metal bracket fixed to the body. This connector has two pairs of the HS Canbus wires running through it.

I have bypassed C112 by soldering the two HS canbus wires. I have bypassed C113 by soldering the four HS canbus wires (access was good enough to do this quite easily with glovebox removed).  I bypassed C90 (in underbonnet fusebox)- I cut the 2 hs canbus wires off plug, extended them and soldered them to the pins in c90 socket. I then trimmed the corner off the c90 plug so I could get the plug back in.  

And Yes I did this - I then took the instrument cluster apart and resoldered all 32 pins on the connector socket on the circuit board. This one is different to all those shown on youtube etc. as the socket is horizontal. All the stuff I have seen about resoldering these have a vertical socket.

But alas, the car is not fixed. It starts, drives (very well first of all, no power problems), but lets you down at awkward moments half a mile later. Engine malfunction. 'u' communication problem fault codes. Perhaps it has an intermittently faulty ECU. I have not checked the wiring between C113 and C90. I can't work out where it goes, can't even see where it goes through the bulkhead. I can see a bunch of wires going through the bulkhead at back of glovebox towards the right but the HS canbus wires are not in that bunch of wires.

But I can't spend any more time on it, I have to spend some time with my family. So I think my brother is going to advertise at a low price to get rid of it, but clearly stating it has what we believe is an intermittent electric fault that renders it unfit for use although it will start and drive.

So the purpose of this post is not to ask for more ideas. It is just here in case it helps anyone else who might be trying to fix their problem and stumbles across this thread. 

 

 

[isetta]

to the person who sent me a PM saying don't give up, look at the connectors under the back seat. I can't work out how to get back to the PM to reply to it. So I am adding this so you know I did not ignore you.

Anyway, after you sent this I have looked under the backseat and under the right side edge of back seat there is a red plastic block connector there with HS canbus wires in it. There is nothing plugged into this connector (I am guessing that if this car had a fluid type DPF that would be plugged in there). I noticed also at this area of the car there are also MS canbus wires running further back from the back seat, I don't know what they would be for. (the car has also had some intermittent MS canbus problems at other times - this shows itself when the indicator dash warning lights dont work, the blue high beam does light does not work, the outside temp is not shown, the red snowflake stays on, the handbrake light stays on, the indicators are not audible - all of these are controlled by the MS canbus and if all these faults show at once it means there is a break between the instrument cluster and the BCM under the glovebox ).

 Having pulled up bits of carpet and removed plastic trim there is more of a labyrinth of canbus wires on this car than I thought. following the path is quite difficult. For example in the loom on the floor just under the front edge of the front passenger seat there are three pairs of HScanbus wires running alongside eachother.

So I am back on it trying to sort it out. And it's going to be radical. Cut the HScanbus wires at the instrument cluster. Solder new wires on the plug, get wires through the bulkhead to the ABS unit (cutting original HScanbus wires off), then round to the electric hydraulic steering pump (cutting original HScanbus wires off), and then to the ECU under the left front wing. (cutting original HScanbus wires off),  All joints will be soldered.

And then on the MScanbus connector C112 will be bypasssed with soldered wires and  the same with any other plugs along the way that I find.

And if that doesn't fix it I will scream very loudly.

I will keep you updated but it might be a while as I won't know if cured until it has had extensive testing.

[Tdci-Peter]

2 hours ago, isetta said:

And it's going to be radical. Cut the HScanbus wires at the instrument cluster. Solder new wires on the plug, get wires through the bulkhead to the ABS unit (cutting original HScanbus wires off), then round to the electric hydraulic steering pump (cutting original HScanbus wires off), and then to the ECU under the left front wing. (cutting original HScanbus wires off),  All joints will be soldered.

Don't forget the Diagnostic connector! That needs the bus also. Otherwise on a 1.8TDCI (without HID, Keyless Go, or Auto transmission), I think that is everything. Use twisted pair cabling of similar sizing to the existing wires.

I didn't think the wiring to the Dosing module would be there on a 1.8TDCI, Ford usually economise on wires and connectors where they can, a dedicated harness saves a few pennies. So that's a good find.

I found it quite easy to push a few more wires through the big rubber grommet in the bulkhead near the PJB on my car.

The MS CAN bus goes to the Park Aid (reversing beeper) in the boot, as well as the front doors (if you have 4 electric windows), Audio system, (& Keyless Go module & CD changer if fitted). It runs from IC to BCM (aka GEM or PJB) overall.

[isetta]

Ah yes Peter, I forgot to mention the Diagnostic socket in my message above. But I had already drawn a plan on a piece of paper and I had put it on there. would have been kicking myself if I had no way of reading the fault codes - but there may never be any fault codes ever again after doing all of this - fingers crossed (unlikely)- but yes, it would be silly to have no diagnostic port.

"The MS CAN bus goes to the Park Aid (reversing beeper) in the boot, as well as the front doors (if you have 4 electric windows), Audio system, (& Keyless Go module & CD changer if fitted). It runs from IC to BCM (aka GEM or PJB) overall. "   ah yes it does have reversing sensors - I had forgotten about them.

"Use twisted pair cabling of similar sizing to the existing wires." What do you reckon the effect of using thicker wire would be? I was going to use thicker wire, not because I thought there would be any benefit but just because that is what I have laying around. I assumed Ford used the thinnest wire that would work for economy/keeping thickness of looms down and not because thicker was detrimental to what goes thorugh the wire. But my theory is all based on normal electric current use eg. 12 volts 21 watt (1.75amp ) bulb at the end of the wire and not how pulses of computer data use a wire.

 

[Tdci-Peter]

8 hours ago, isetta said:

"Use twisted pair cabling of similar sizing to the existing wires." What do you reckon the effect of using thicker wire would be? I was going to use thicker wire, not because I thought there would be any benefit but just because that is what I have laying around.

In reality, the wire size won't make much difference, within sensible limits.

In theory, the bus is a transmission line, like a coax cable. The high frequency impedance of the line is determined by the conductor diameter, the distance apart, and the di-electric constant of the insulation. Ideally this impedance is about 120 ohms, which matches the terminating resistors, and this prevents echoes bouncing off each end, blurring the sharp edges of each transmitted bit. In effect the end with its resistor, looks like an infinite continuation of the line, so no echo.

But the CAN bus only works at 500k bits/sec, unlike old TV coax at 100MHz to 1000MHz, or USB1 at 12M bits/sec or USB2 at 480M bits/sec. Makes CAN look slow and old (bit like me on a bad day!).

Also CAN has lots of nasty spurs and intermediate connections, which muck up the impedance of the line anyway. Also I just noticed the wiring diagram gives 0.5mm^2 for HS-CAN under the bonnet, and 0.35mm^2 in the cabin, so they are not too fussy. I think anything from 0.35mm^2 to about 0.75mm^2 will be fine.

The twisting is more important, the impedance can vary hugely if the wires separate a lot, and it cancels out most interference (incoming or outgoing).

 

[isetta]

Thanks Peter. I will be soldering the wires this evening as long as it's not raining.

[Micro]

On 7/10/2019 at 2:10 PM, isetta said:

Ah yes Peter, I forgot to mention the Diagnostic socket in my message above. But I had already drawn a plan on a piece of paper and I had put it on there. would have been kicking myself if I had no way of reading the fault codes - but there may never be any fault codes ever again after doing all of this - fingers crossed (unlikely)- but yes, it would be silly to have no diagnostic port.

"The MS CAN bus goes to the Park Aid (reversing beeper) in the boot, as well as the front doors (if you have 4 electric windows), Audio system, (& Keyless Go module & CD changer if fitted). It runs from IC to BCM (aka GEM or PJB) overall. "   ah yes it does have reversing sensors - I had forgotten about them.

"Use twisted pair cabling of similar sizing to the existing wires." What do you reckon the effect of using thicker wire would be? I was going to use thicker wire, not because I thought there would be any benefit but just because that is what I have laying around. I assumed Ford used the thinnest wire that would work for economy/keeping thickness of looms down and not because thicker was detrimental to what goes thorugh the wire. But my theory is all based on normal electric current use eg. 12 volts 21 watt (1.75amp ) bulb at the end of the wire and not how pulses of computer data use a wire.

 

A cheap source of twisted-pair wiring would be a long ethernet cable (round style for ease of disassembly). Believe Cat-5e is 0.5mm2

Best of luck to you!