Having a right hard time finding this one!
I'll give the full history as it might be relevant.
I had intermittent fault where I would get the dsc light in the middle of the dash come on and sometimes hdc inactive. when I plugged my hawkeye in I would get in the air suspension fault code menu "sporadic short to positive not currently present"
Then driving home from work one day the transmission decides to go. Luckily for me only the torque converter. I replaced the torque converter, the tcc solenoid, the transmission oil and filter in my mates dry workshop which fixed that problem.
I couldn't clear the abs light/hdc fault at the time and the hawkeye kept coming up with a comms error but drove the old girl home without any other problems. I drove it to work a couple of times with the warning lights on but no other problems. I came out to it the other week and it was a little frosty so i started her up and left her idling for a couple of minutes, when I came back out I noticed all the brake lights were on, I tried ignition on/off a couple of times but they stayed on. I ended up taking the daughters car.
what i've noticed is that in ignition position 1 the brake lights work as they should, but 5 seconds after i start the engine the brake lights come on and stay on, i've still got the hdc inactive and the usual abs/dsc warning lights on the dash. the only fault code I get from the hawkeye is "can bus sporadic short to positive currently present" with the ignition on, with the ignition off I can clear the fault.
I've checked the connectors on the transmission and transfer box, given them a clean with switch cleaner and dried with compressed air. Also done the same on the abs connector as i've had some moisture in there before which caused some bother.
I'm completely out of ideas and just hope that somebody has come across this before or can give me a pointer as to where to check next.
thanks in advance

Sounds to me like your Hawkeye is playing up... With that array of lights you would think it would have more faults logged.... Pete

__________________________________________________
2014 L405 Autobiography SDV8 4.4 Loire Blue Ebony interior
2011 L322 Vogue SE 4.4 TDV8 Baltic Blue. Parchment over Navy Interior. Sold
2012 L322 Autobiography 5.0 Supercharged Ipanema Sand, Jet Interior. Sold
2002 L322 Vogue 4.4 V8 Epson Green, Ivory over Aspen Interior (Fatty Offroader) Sold
-Click for Project Fatty off roader-

Sounds like you have a short to positive that's turning on the brake lights, so what the Hawkeye is reporting is correct.
As the braking system controls the HDC and Traction control then those other errors also make sense.
Unfortunately not an easy one to sort!
Grabbing at straws but brake light switch? Either that or relook at the ABS module and wiring.

haylands, thought that at first or maybe the red adapter but everything else i.e. service functions and other test work fine so pretty sure the hawkeye is fine.
suspected brake switch weejock but the lights work fine with the ignition in position 1 plus the shifter lock is ok which utilizes the same switch so ruled that out, think you're right that it's a fault somewhere in the abs/eas but it's just where?!!
does anyone know what else puts the brake lights on, for example do they come on with hill decent or when selecting ride heights?
short of doing the parts change roulette with abs module etc i'm kinda out of ideas

They do come on with HDC, mine came on on their own with the ignition off after I drowned the car in a river... could be water in your electrics somewhere, check the carpets for dampness...  Pete

__________________________________________________
2014 L405 Autobiography SDV8 4.4 Loire Blue Ebony interior
2011 L322 Vogue SE 4.4 TDV8 Baltic Blue. Parchment over Navy Interior. Sold
2012 L322 Autobiography 5.0 Supercharged Ipanema Sand, Jet Interior. Sold
2002 L322 Vogue 4.4 V8 Epson Green, Ivory over Aspen Interior (Fatty Offroader) Sold
-Click for Project Fatty off roader-

re brake light on, check the body control ECU in the passenger footwell, it might have got wet from blocked sunroof drain pipes..

also check for water ingress and in the rear near side cubby hole.. ... - .- -.




Y. O. L. O.
.

I like a challenge and this could be a complex one!

The brake lights do not go through the Body Control Unit, the only lights the BCU controls are some interior lights.
The brake lights are operated by the Light Check Module, it controls all exterior lights and most interior and is located at the base of the drivers A pillar. The LCM operates the brake lights when the brake pedal switch is operated or when HDC is active and the ABS ECU sends a brake light command to the LCM.
The brake pedal switch is in fact two switches in one unit. One switch is Normally Open and grounds when pressed, this acts as the standard brake light pedal switch and is also used for brake pedal input sensing for other ECU's (ABS, EAT, Air Suspension, Steering Angle Sensor, Transfer box and Instrument Pack). The other switch is Normally Closed, it opens when the pedal is pressed and cuts a 12v feed (via fuse 9) to the engine ECU.
Given your symptoms (brake lights come on and stay on after 5 seconds with ignition on) then as you suspect the brake light switch should be OK (if the lights were on all the time with no keys in then it indicates fuse 9 gone or switch problem).

It sounds like there is a short from positive to the CAN bus (from the fault code) which is giving a confusing signal relating to the HDC (as HDC is the only other system that turns on the brake lights).
On the ABS ECU, Pin 7 (yellow/brown 0.35mm2) is the HDC active output from the ABS ECU to the LCM (turns on the brake lights) and that is right next to two power supply pins (pin 6 and 23) so maybe shorting out. Pin 7 is not a CAN bus connection though, it's hardwire so won't give a CAN bus error.
Pin 24 (yellow/black 0.5mm2) is a CAN bus high and again that is right next to power supply pin 23.
Pin 40 (yellow/brown 0.5mm2) is a CAN bus low and sits next to pin 39 DSC sensor supply (5V ref probably).
If they are shorting out to adjacent positive pins due to damp or old damp residues/corrosion then you could get an error.

I know if it was me that is the first place I would be looking. Disconnecting pin 7 on the ABS ECU will deactivate the brake light signal from the HDC to the LCM (brake lights will still will work from the brake pedal) and will determine if it's an ABS ECU issue or LCM. It is possible the LCM is faulty but it shouldn't throw up ABS light faults hence why I think it's an ABS issue.

Given your previous issue with damp in the ABS connector I would be looking at that first. It's not just the connector that may be damp, it could have tracked inside the ECU itself.
It could be an issue elsewhere on the CAN bus system though, especially as you've had other sporadic faults on the CAN bus. All CAN bus wiring is the same colour, CAN Bus high is yellow/black 0.5mm2, CAN Bus low is yellow/brown 0.5mm2.
It could also be multiple unrelated faults....which would be a right pain!

For waterproofing electrical connections try 'Corrosion X Aviation', I know Haylands likes it

Details from the WSM that might help:


DESCRIPTION
Brake Lamps
The brake lamps are active with the ignition switch in the 'auxiliary' or 'ignition' positions. The
Light Check Module (LCM) receives an input from the brake switch, which is used as a signal
to activate the brake lamps. When Hill Descent Control (HDC) is active, the ABS ECU
outputs a signal on a separate hardwired connection to the LCM to activate the brake lamps
when the HDC function is operating.

Brake Lamps
The LCM (C2040) monitors the condition of the brake pedal via the brake pedal switch
(C0075) on a UR wire. When the brake pedal is pressed, the switch contacts close and an
earth path is created on an NB wire. Sensing this, the LCM (C0937) provides a feed to the
following on BU wires:

The RH brake lamp (C0125)

The LH brake lamp (C0121)

The Centre High Mounted Stop Lamp (CHMSL) (C0613).
All are earthed on N wires.
When HDC is functioning, the ABS ECU (C0506) outputs a signal to the LCM (C2040) on a
YN wire. When the LCM receives this signal, it operates the brake lamps as described
above. For more information on ABS operation, refer to the Anti-Lock Braking System
(ABS) section of this manual, and the Brakes section of the System Description and
Operation Workshop manual.
+ ANTI-LOCK BRAKING SYSTEM (ABS).



ABS ECU details:

Click image to enlarge

Click image to enlarge

^^^ Stunning  .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember
Volvo V70 P2 2006 2.4 Petrol 170bhp Estate SE
MG Midget Mk1 1962

Previous: L322 Range Rover TDV8 3.6 2008; L322 Range Rover TD6 3.0 2002; P38A Range Rover V8 1999

Weejock you are a deity.

I checked and was getting a signal on the ABS ECU for the stop lights, they returned to normal function when i disconnected the plug from the abs ecu. also through up transmission failsafe mode for some reason. tried disconnecting the signal wire from the plug and got normal function but still short to positive.
decided that the ABS ECU was the culprit and got a whole ABS unit off the bay of fleas for £150.
I replaced the whole ABS unit and bled the brakes through. recalibrated the steering angle sensor (would appear this works through the ABS ECU) and the old girl is fixed.
just got the dreaded MOT next week

Thanks for all your help, it's very much appreciated

No problem, glad you got it sorted!
Electrical issues like that can be a right head scratcher especially when CAN bus is involved, there's something to be said for one wire does one job!

@Weejock - great bit of detective work there  Howard
____________________________________________________
2002 4.4 V8 LPG Tartarini
Have RSW AllComms in Cheshire J17 M6 - happy to help.
*Gone: Classic Vogue SE Auto V8 3.9

Great posts helped me diagnose the exact same problem with my l322 td6 abs ECU faulty
 Range Rover Vogue TD6 2006