Disco 2 Checking wiring loom from XYZ switch

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RIchard Savage

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Location
Sevenoaks
2003 D2 is grounded with flashing M+S lights which appear when I start to pull away in D and gearbox selects 3. Hawkeye reveals P0705 14 as a hard fault. The XYZ switch has been replaced with a tested used switch but the fault persists. My workshop bloke recruited the help of a chum who is an LR tech to fit the switch. He declared the gearbox to be FUBAR but before I either scrap the D2 or fit an Ashcroft exchange I think that I should chase the loom from the switch back to the BCU. I have the wiring diagrams but can anyone point me towards more helpful resources? I think I saw an article with pictures showing how to check which pins and expected values on 't web but cannot for the life of me find it.
 
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Have you physically checked the loom on the top of the boxes? Notorious for the P clip chafing and causing probs.
Easier than fri ggin around in other ways!
 
RIchard Savage said:
2003 D2 is grounded with flashing M+S lights which appear when I start to pull away in D and gearbox selects 3. Hawkeye reveals P0705 14 as a hard fault. The XYZ switch has been replaced with a tested used switch but the fault persists. My workshop bloke recruited the help of a chum who is an LR tech to fit the switch. He declared the gearbox to be FUBAR but before I either scrap the D2 or fit an Ashcroft exchange I think that I should chase the loom from the switch back to the BCU. I have the wiring diagrams but can anyone point me towards more helpful resources? I think I saw an article with pictures showing how to check which pins and expected values on 't web but cannot for the life of me find it.
Click to expand...
P0705 is purely electrical, nothing to do with the 'box itself, so it can't be FUBAR on the basis of that fault code (comes up occasionally on my auto too).

Do you have a Nanocom? You can get live data from the XYZ switch as you move the gear lever. You won't always see the problem with the loom where it goes over the transfer box, so you will need some diagnostics to track it down. By the way, the auto box has its own ECU, not the BCU. It is under the passenger seat.

I'm sure sierrafery will jump in here too with even more information. But I bet the box is not FUBAR!

Cheers.

PP.
 
Hi, We had this flashing lights problem once very intermittant. D2 2004. here is a copy of the notes I made at the time.
Fault- Gearbox Sport & Manual Lights Flashing (Green) :- Date 4/5/2020

Lynx Diagnostic Gearbox ECU DTC’s

Error Code P0705 Position Switch Monitoring ( Permanent)

Fault not currently present & continuous.

Live Tests Gear Switch XYZ

Binary Position Codes P=1000, R=100, N=1110, D=1011, 3=111, 2=1, 1=10 All Correct

------------------------------------------------------------------------------------------------------------------

Internet Cause’s

P0705 (14, 23) * Gear position switch, incorrect outputs Maintains current gear in low range, limp home mode in high range. Shift pressure to maximum, harsh gear shifts/engagement. On Off

My Suspicions

Suspect High Throttle when shifting from Reverse to Drive --- Operator Error !

Heavy Thud/Jerk on change over
Hope this helps, Take Care
 
PopPops said:
P0705 is purely electrical, nothing to do with the 'box itself, so it can't be FUBAR on the basis of that fault code (comes up occasionally on my auto too).

Do you have a Nanocom? You can get live data from the XYZ switch as you move the gear lever. You won't always see the problem with the loom where it goes over the transfer box, so you will need some diagnostics to track it down. By the way, the auto box has its own ECU, not the BCU. It is under the passenger seat.

I'm sure sierrafery will jump in here too with even more information. But I bet the box is not FUBAR!

Cheers.

PP.
Click to expand...

I have Hawkeye, not Nanocom.
Indeed, I was thinking that I need to 'bell' the loom through whilst applying a bit of judicious wiggling. Needless to say, it's hooning down with rain here :-(
I also doubt the diagnosis of FUBAR until I have proved that the 'box ECU is being communicated with by the XYZ switch and is responding :)

Cheers
 
ES4 said:
Hi, We had this flashing lights problem once very intermittant. D2 2004. here is a copy of the notes I made at the time.
Fault- Gearbox Sport & Manual Lights Flashing (Green) :- Date 4/5/2020

Lynx Diagnostic Gearbox ECU DTC’s

Error Code P0705 Position Switch Monitoring ( Permanent)

Fault not currently present & continuous.

Live Tests Gear Switch XYZ

Binary Position Codes P=1000, R=100, N=1110, D=1011, 3=111, 2=1, 1=10 All Correct

------------------------------------------------------------------------------------------------------------------

Internet Cause’s

P0705 (14, 23) * Gear position switch, incorrect outputs Maintains current gear in low range, limp home mode in high range. Shift pressure to maximum, harsh gear shifts/engagement. On Off

My Suspicions

Suspect High Throttle when shifting from Reverse to Drive --- Operator Error !

Heavy Thud/Jerk on change over
Hope this helps, Take Care
Click to expand...


Thank you.
Having had several auto RR and now the D2 and hating the 'shunt' between D and R I am always very gentle when engaging D or R (no throttle pressure and pausing between the two).
Hawkeye is reporting no infornation regarding the position codes, i.e. 'zeros' as far as I can remember :-( I will record them when I next venture into the rain.

Cheers
 
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The output from the xyz switch goes to both the bcu ecu (front passenger foot well) and the automatic transmission ecu (under front passenger seat) splitting under the console between the front driver and passenger seats.
With a nanocom you can read the outputs from the xyz switch received by both ecus and compare the results with each other and the table of expected results found in, rave or workshop manual.
A fault in the signal received by either ecu will cause flashing m+s lights and limp mode.
Cycle through all gear selector positions and record all outputs from xyz switch received by both ecus then compare with table of expected results from rave or workshop manual to identify where fault is.
NOTE with my nanocom I had to reverse the wxyz scale to read zyxw on the results from one of the ecu readings to get a true result, think it was bcu ecu but it was so long ago not 100% certain.
Faulty signal received by one ecu only problem in wiring circuits after split, same faulty signal received by both ecus problem in xyz switch or wiring circuits between xyz switch and split.
If no signal received by neither ecu for any forward drive gear position may indicate that the xyz switch is not receiving any power from the bcu ecu.
 
ROY SIMPSON said:
The output from the xyz switch goes to both the bcu ecu (front passenger foot well) and the automatic transmission ecu (under front passenger seat) splitting under the console between the front driver and passenger seats.
With a nanocom you can read the outputs from the xyz switch received by both ecus and compare the results with each other and the table of expected results found in, rave or workshop manual.
A fault in the signal received by either ecu will cause flashing m+s lights and limp mode.
Cycle through all gear selector positions and record all outputs from xyz switch received by both ecus then compare with table of expected results from rave or workshop manual to identify where fault is.
NOTE with my nanocom I had to reverse the wxyz scale to read zyxw on the results from one of the ecu readings to get a true result, think it was bcu ecu but it was so long ago not 100% certain.
Faulty signal received by one ecu only problem in wiring circuits after split, same faulty signal received by both ecus problem in xyz switch or wiring circuits between xyz switch and split.
If no signal received by neither ecu for any forward drive gear position may indicate that the xyz switch is not receiving any power from the bcu ecu.
Click to expand...
It's the auto box ECU which is reversed, I didn't check the BCU, I noted this with my Nanocom last year and posted on here somewhere. Sierrfery confirmed RAVE is correct and Nanocom wrong. I did report it to Black Box (it was confirmed on their forums too), but I don't think anything happened.

Cheers.

PP
 
Hi, Good advice from Roy S I didn't realise the codes were sent to the BCU as well as the Gearbox Ecu. As the binary codes are live you should be able to monitor them while wiggling the harness to see if they change, checking all positions. If your lucky you might be able to locate the position of the break in the harness before you tear it apart. Its more likely to be a wiring fault rather than the Gearbox. Do the codes that are sent to the BCU drive the gear position LCD display on the dash?
 
ES4 said:
Hi, Good advice from Roy S I didn't realise the codes were sent to the BCU as well as the Gearbox Ecu. As the binary codes are live you should be able to monitor them while wiggling the harness to see if they change, checking all positions. If your lucky you might be able to locate the position of the break in the harness before you tear it apart. Its more likely to be a wiring fault rather than the Gearbox. Do the codes that are sent to the BCU drive the gear position LCD display on the dash?
Click to expand...

The gear selection codes appear in the LCD until I select D and move away.
 
RIchard Savage said:
The gear selection codes appear in the LCD until I select D and move away.
Click to expand...
This business of "until I move away" or "until I reverse" or in one other case we had, "until I move off turning to the right".
When the inertia of the weight of the gearbox/tranny box acts on it to keep it from moving at the exact moment the vehicle moves is often the moment when the loom moves relative to the body of the car and the chafed wires open up or touch others or whatever.
Just sayin;)
 
Stanleysteamer said:
This business of "until I move away" or "until I reverse" or in one other case we had, "until I move off turning to the right".
When the inertia of the weight of the gearbox/tranny box acts on it to keep it from moving at the exact moment the vehicle moves is often the moment when the loom moves relative to the body of the car and the chafed wires open up or touch others or whatever.
Just sayin;)
Click to expand...

Bloody cars . . .
 
Hi, it does sound movement related you shouldn't lose the LCD info, can you try to reproduce the fault by moving forward / reverse and when you lose the LCD check the codes when the LCD is off and see if they are correct, When the LCD is off does it not cause the M&S lights too flash also. If the Harness goes to the BCU and the Gearbox ECU as Roy S said could it maybe break/ Chaf in such away that you corrupt the signal to either or both. When the M&S lights come on is the LCD off as well. in which case it could be faulty before the harness divides.ie nearer the XYZ switch.
 
ES4 said:
Hi, it does sound movement related you shouldn't lose the LCD info, can you try to reproduce the fault by moving forward / reverse and when you lose the LCD check the codes when the LCD is off and see if they are correct, When the LCD is off does it not cause the M&S lights too flash also. If the Harness goes to the BCU and the Gearbox ECU as Roy S said could it maybe break/ Chaf in such away that you corrupt the signal to either or both. When the M&S lights come on is the LCD off as well. in which case it could be faulty before the harness divides.ie nearer the XYZ switch.
Click to expand...
Afraid to say I will laugh if all this comes down to a simple old skool chafed wire that has been missed by an LR specialist.
shouldn't laugh but may not be able to help myself!
But at least it'll be a cheap fix if that is what it turns out to be.;)
 
Stanleysteamer said:
Afraid to say I will laugh if all this comes down to a simple old skool chafed wire that has been missed by an LR specialist.
shouldn't laugh but may not be able to help myself!
But at least it'll be a cheap fix if that is what it turns out to be.;)
Click to expand...

I will be delighted to join you in the laughter - but mine will be from relief.
 
I'll be digging into it as soon as I can and will report back. Unfortunately, that's unlikely to be in the next couple of weeks - unless I become tremendously enthusiastic in the evenings - because my weekends are fully booked. However, I am very appreciative of your encouraging words. :)
 
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