XYZ switch and no front electric windows. Help!

Hi all,

First post here, so thanking everyone in advance for any help.

I'm tearing my hair out with a TD5 Disco 2 Auto we use at our sailing club for shunting round trailers.

Out of the blue the two flashing green transmission lights appeared on the dashboard and the gearbox went into limp mode. At the same time the front windows stopped working.

Nanocom threw up a P0705 Position sensor error.

Clearing the fault, resulted in it immediately returning.

So far we have :

Swapped the good XYZ sensor from our other Disco 2. It made no difference. The one off the faulty Disco, worked perfectly on the good donor Disco so we have ruled out the sensor itself.

Checked the wiring loom on top of the gearbox for any chafing, which there isn't and also checked for continuity on all the wires from the XYZ sensor and the other transmission wires running through the loom back to the connector blocks under the centre console. All have good continuity.

Swapped the gearbox ECU off the good Disco onto the poorly one. It made no difference and the one off the poorly one works fine on the good one.

When trying both front front windows there are no relay clicking sounds coming from the BCU module. Both windows worked correctly before the green flashing transmission warning lights appeared.

Checked the battery voltage and ran a direct earth from the battery to the BCU and gearbox loom earthing points. Made no difference.

Could it be a faulty BCU or damage to the wiring somewhere between the centre console and the passenger footwell where the BCU is located?

Any other ideas?

Is it possible to swap out the BCU on a plug and play basis with a known fully functional one or would we need to use Nanocom to configure it? Thinking we could try the BCU off the working Disco.

The fact that the front windows are controlled by the BCU and also the XYX sensor is linked to the BCU makes me think the gearbox and electric window faults are not coincidental and must be related.

I've googled the topic to death and can't find any info on a combination of P0705 fault codes and dead front electric windows.

Any pointers would be much appreciated!!!!!!
Thanks

lohr5000 said:

Checked the wiring loom on top of the gearbox for any chafing, which there isn't

Click to expand...

Have you actually taken the horrible thing off and opened up the exterior insulation to check it properly, or did you just give it a bit of a once over, maybe in situ?
It is the P clip that causes the damage and often it cannot be seen unless the above is done.

And is this a sea sailing club or a freshwater sailing club?!

Welcome to the forum by the way!
and there is an "Introduce yourself " section which you might like to visit!

Stanleysteamer said:

Have you actually taken the horrible thing off and opened up the exterior insulation to check it properly, or did you just give it a bit of a once over, maybe in situ?
It is the P clip that causes the damage and often it cannot be seen unless the above is done.

And is this a sea sailing club or a freshwater sailing club?!

Click to expand...

Thanks for the reply.

We didn't remove the loom completely, but we did detach the P clip and cut open the insulation to inspect the wiring for about 2 inches either side of where the P clip was located. No sign of any damage to the individual wires.

To gain access to the loom, I drilled out all the rivets holding the plate which supports the transfer box and main gear shift levers.
To make access easier to the XYZ sensor, I cut a flap in the transmission tunnel with an angle grinder!!! That's the beauty about running clapped out Disco's at the Sailing Club. We strip out all the carpets, rear seats and anything else that could soak up water or get in the way.

When doing the continuity check on the XYZ sensor and the other multipin connector attached to the gearbox to the right of the XYZ sensor back to the multipin connectors under the centre console, we waggled the loom whilst testing to see if we got any breaks in the continuity. I plan to double check the continuity again when we return next week for Round 2 of the battle!!

Freshwater inland reservoir, so at least we don't have saltwater corrosion to add to the challenges.
Lucky to have three TD5 Disco 2 Autos and a venerable 300tdi Disco 1 Auto, so I can swap components if needed to fault find.
We also have a Nanocom for the TD5's , although I am still learning how to use it effectively.

lohr5000 said:

Thanks for the reply.

We didn't remove the loom completely, but we did detach the P clip and cut open the insulation to inspect the wiring for about 2 inches either side of where the P clip was located. No sign of any damage to the individual wires.

To gain access to the loom, I drilled out all the rivets holding the plate which supports the transfer box and main gear shift levers.
To make access easier to the XYZ sensor, I cut a flap in the transmission tunnel with an angle grinder!!! That's the beauty about running clapped out Disco's at the Sailing Club. We strip out all the carpets, rear seats and anything else that could soak up water or get in the way.

When doing the continuity check on the XYZ sensor and the other multipin connector attached to the gearbox to the right of the XYZ sensor back to the multipin connectors under the centre console, we waggled the loom whilst testing to see if we got any breaks in the continuity. I plan to double check the continuity again when we return next week for Round 2 of the battle!!

Freshwater inland reservoir, so at least we don't have saltwater corrosion to add to the challenges.
Lucky to have three TD5 Disco 2 Autos and a venerable 300tdi Disco 1 Auto, so I can swap components if needed to fault find.
We also have a Nanocom for the TD5's , although I am still learning how to use it effectively.

Click to expand...

I would get "live data" from the XYZ switch from the Nanocom and compare it with what it should be in RAVE. Depending on what version Nanocom you have, it may have WXYZ reversed, mine did. May give you a clue what the EAT is objecting to.

The table from RAVE is attached.

Good luck.

PopPops said:

I would get "live data" from the XYZ switch from the Nanocom and compare it with what it should be in RAVE. Depending on what version Nanocom you have, it may have WXYZ reversed, mine did. May give you a clue what the EAT is objecting to.

The table from RAVE is attached.

Good luck.

Click to expand...

Thanks for this. Will do so when we return to the vehicle next week and let you know what we find.

lohr5000 said:

The fact that the front windows are controlled by the BCU and also the XYX sensor is linked to the BCU makes me think the gearbox and electric window faults are not coincidental and must be related.

I've googled the topic to death and can't find any info on a combination of P0705 fault codes and dead front electric windows.

Click to expand...

Hi, unfortunately the BCU is very suspect at this point

lohr5000 said:

Is it possible to swap out the BCU on a plug and play basis with a known fully functional one or would we need to use Nanocom to configure it? Thinking we could try the BCU off the working Disco.

Click to expand...

Plug and play is out of question, programming is compulsory ... simplest for you would be to send the BCU to be checked there: https://www.ebay.co.uk/itm/133115857675 then it will be plug and play

sierrafery said:

Hi, unfortunately the BCU is very suspect at this point

Plug and play is out of question, programming is compulsory ... simplest for you would be to send the BCU to be checked there: https://www.ebay.co.uk/itm/133115857675 then it will be plug and play

Click to expand...

Thanks for this.

Do you know if there any simple things like BCU connector pin voltage readings, earthing points, fuses, etc that we could check first to rule out anything basic before sending off the BCU to the company in your link? Am I right in thinking that because Nanocom seems to connect to the BCU when I select the Valeo BCU option, it must be at least partially operational?

Is there a step by step guide anywhere on how to program a BCU using Nanocom? I'd be happy to capture all the settings on the BCU in the working Discovery, then use that BCU it in the faulty Discovery, programming as required. If this is possible, and the swapped out BCU works in the faulty Disco, then it would prove that the fault is with the BCU.

Does nothing work if you just put a different BCU into the vehicle? The donor BCU in the good Discovery is also a TD5 Auto of the same age. If all we could achieve in doing so was to prove that the other BCU was the cause of the P0705 and front window fault, then it would be worth sending the faulty BCU off for repair.

Sorry for all the dumb questions but I am still stepping onto the 1st rung of the ladder when it comes to Disco 2 electronics!

You can't troubleshoot a partially working BCU with multimeter as long as there are two completely differnt systems involved like autobocx and windows unless you know well what's what and work by the diagrams... if you simply plug in an unsynk'd BCU it will become immobilised. No step by step programming guide anywhere, i have not enough energy nor mood to make one, you can figure it out yourself if you know how all the systems are working and read the nanocom user guides for all of them https://www.nanocom-diagnostics.com/downloads you can play with the emulator for training first

for a basic test to not mix things up bad as both vehicles are similar disconnect battery negative lead first(never unplug/plug any ECU/BCU/fusebox with battery connected) then after the BCU swap and battery reconnection turn ignition on 2 let it so 5 minutes(DO NOT ATTTEMPT TO CRANK) then go with nanocom to engine ECU - utility - learn security code, once it's confirmed, exit the menus, unplug nanocom, start the engine and see if the faults are still present, if theyr'e gone the BCU is at fault...if no change the BCU is ruled out, .... you'll have to make the donor vehicle as well to re- learn the security code after you put the BCU back

Thanks again sierraferry. A massive help.

I think we will try your suggestion as follows :

for a basic test to not mix things up bad as both vehicles are similar after the BCU swap turn ignition on 2 let it so 5 minutes(DO NOT ATTTEMPT TO CRANK) then go with nanocom to engine ECU - utility - learn security code, once it's confirmed, exit the menus, unplug nanocom, start the engine and see if the faults are still present, if theyr'e gone the BCU is at fault...if no change the BCU is ruled out, .... you'll have to make the donor vehicle as well to re- learn the security code after you put the BCU back

These Disco's are used purely off the highway and we have pulled most of the fuses powering lights, wipers, heated screens, radios, indicators and other ancillaries to prevent drivers flattening the batteries. We have also disabled a lot of the alarm functions using Nanocom.

All they need to do is to stop, start and drive!!!
So not too worried about a lot of the settings in the BCU, so long as the basics work.

Problem solved.

Before swapping out the BCU from the other Disco, I thought I should check all the fused power supplies and relays, linked to the BCU/ECU.

Turns out the culprit was a faulty relay R4 in the passenger compartment fuse box.
As soon as I swapped the relay for a similar one out of the other Disco, everything was back to normal.

The surgery to first locate and check the XYZ switch and loom for chafing was a bit brutal, but at least the XYZ switch will now be easy to replace if it ever does go wrong

Although Nanocom is great, it did send me on the wrong track with the P0705 error. Lesson learned to check the obvious stuff 1st!!!!

lohr5000 said:

Turns out the culprit was a faulty relay R4 in the passenger compartment fuse box.

Click to expand...

Now that's the most enormous oddity i've ever seen(unless you confused R4 with other or the diagrams are wrong) as R4 is for ignition coils for V8's, it not supposed to have any function for a Td5... i dont even have it there

remove it see what happens

Next time I go to the sailing club, I will double check that it was the R4 position. I am pretty sure it was marked as ignition, with the one above it marked on the schematic for electric windows. It was a large size relay and identical to R4, the cooling fan relay in the fuse box in the engine compartment fuse box.

I did find a RAVE wiring diagram for a D2 and if the relay is the one I have highlighted below (which as you say does connect to the ignition coils as well) then it appears to also have a feed going to the "ECU ELECTRONIC AUTOMATIC TRANSMISSION (D123)"

Could the low current side of this relay have failed causing a break in the feed to the gearbox ECU?
I haven't traced all the wiring on the diagram though to see how it could also affect the front windows!!
A mystery.

And yes, good idea @sierrafery. I'll pull the relay I replaced and see if the original fault condition returns.

As you can see the power from F24 splits to R4 relay's coil and to the EAT ECU and ECM while the power through the contact only to ignition coils by F14 so the only possibility for this relay to mix up the management would be that it's coil to have a short and create a slight voltage drop on that circuit to mix up the EAT ECU which is very sensitive to power supply but not the ECM too as you didnt get any engine fault code... If there is no hidden wiring issue on that circuit removing that relay should make no difference but you should check the old relay's coil resistance to see cos this fault is very strange and would be good to know it can happen.

I will check the original relay when I am next at the club. I can compare the resistance to that of the good relay that replaced it.

I did notice that the relay was warm to the touch when I pulled it which would perhaps support your idea about the relay coil failing

Just hoping now that the relay was the culprit and that it isn't going to fail with the same fault again over the weekend when in use.

I stopped and started the vehicle a few times today after we put it back together and drove it round over some pretty bumpy ground for a few minutes. No issues at all and everything was working correctly including the front windows, the dashboard gear selector shift LCD indicator and the little red gear position indicator lights on the auto gear shift console.

If it works the same with it removed(which it should) let it out as for the Td5 is 100% useless, it's just an unnecessary load on that circuit

Very strange. As you advised, the vehicle runs fine with the relay removed. And on checking one of the other TD5s it doesn't have that relay fitted on the passenger fuse box.

I checked the resistance on the relay I thought was faulty. It reads 96 ohms. The good relay I substituted it with reads 94 ohms.

I have had the suspect relay energised directly from a 12v supply across pins 1 and 2 for 30 minutes and it is drawing around 120 milliamps which I would expect.. At no time did it fail/short.

The good relay draws a similar current.

So yes, it would seem as though the relay has nothing to do with the issue.

It is strange though that as soon as I swapped the relay, everything worked again.

I am now wondering if there might be some corrosion, bad contacts or other damage to the passenger fuse box. Moving the fuse box slightly when pulling the relay may have restored a bad contact?

I've tried shaking the fusebox this morning but I can't replicate the fault and I reseated fuse 24 to see if that was suspect. It made no difference.

When we had the fault, I also tried connecting a mains powered boost starter to the battery to increase the voltage, thinking if the vehicle battery was weak this might affect the electronics. But it made no difference.

So still a mystery. We will keep using the vehicle and see if the fault returns.

Any other ideas sierrafery and thanks again for your help so far

I've kind'a expected that ... unfortunately it seems there was a bad contact or short somewhere which fixed itself while you made all those measurements and jiggled the wirings, if the fault comes back the first step would be to rule out the IDM and BCU, better one of those than a hidden wiring issue