Hi guys, I need some help with a curious fault I'm getting on my 2005 LR3 TD6 2.7

I've had some brake work done and since then I've had an HDC error, but it only happens when I turn the headlights on or when they come on automatically. If the lights are off, no problem, drives like normal. I noticed that one of my sidelight bulbs was out, so I replaced both as a pair with OEM bulbs - that didn't solve the problem. I've replaced the brake switch about 6 months ago when the same fault happened, that fixed it so I thought I'd give this a go again - this time I used the LR official part at a ripoff 35 quid, replaced all brake bulbs aswell with OEM just to be safe! Seemed to work when I tested it, so thought the problem fixed.

Just went to drive it a couple hours later and the lights all came on, so I did a reset, key off, out, back in and on, and lights turned on, no error... moment I took my foot off the brake, error. So I tested a few times and the problem seems to now only occur when the brake is pressed down and thusly, the brake light switch is extended and not depressed. Seems like a brake might be sticking at the back but no noise currently, read on here that someone had a sticking caliper after brake work and that might be causing it but this is unlike any of the dozens of threads which all just say to replace the brake light switch. I need help, my mind is at a dead-end.

 

I'd suggest a very careful look at the wiring diagram and try to see what stepping on the brake does to the various computers in the vehicle. It sounds like an electrical problem, but with the communication busses between the various microcontrollers so interconnected, you really need to identify what kinds of error codes are coming up. Sorry if this sounds redundant, but LR3 (D3) electrical gremlins are notoriously labour intensive to troubleshoot, good luck...

 

Thanks for the advice ENB - I've had a look at some diagrams already and there is a loom under the footwell, running along the sills front to back that is notorious for getting wet, especially if you have some rust under the sills and its very wet. It's been VERY wet in south devon the last few weeks and the day the car was dropped back to us after it's brake work was hammering it down all day and we had to drive through a small flood.
Going to check the carpets and see if there is any wet patches and check the sills for water ingress.

 

Hi Charles...
Sounds like a good plan, these modern (since about 2004) vehicles with CAN bus communications don't take much of an electrical problem to cause unbelievable difficulties and frustration. I hope you are able to resolve this fairly quickly... A good code reader will assist in getting you to the root cause but sometimes electrical problems will send you off on a wild goose chase, so first check out the wiring, exactly as you have decided...
Eric...

 

I'd be checking the wiring around the brake switch, when my switch went bad it was as soon as i touched the brakes.Your issue is in reverse so a thorough check of the wiring in that area would be a good start.

 

Hi Eric, Yeah it is turning in to a bugger. Just to be safe I picked up a genuine LR brake light switch in case I got unlucky and got a duff one third party. Sadly, didn't work. Tomorrow, I'm going to pick up some OEM bulbs whilst getting my tyres done and change all the rear bulbs to LED ones, justtttt to tick that off the list. No water ingress found yet, so looks like it could be a damaged loom. If the bulbs make no difference, then I will investigate it further. Got an LR indie specialist booked at the start of January to diagnose if I can't work it out before then. Thanks for replying though and for the advice!

 

Thanks Loan - anything in specific I'll be looking for?

 

the switch has 2 circuits, 1 for brakes and the other for the cruise control functions. Possibly a short in one of the circuits so trace each one as far as you can then check a wiring diagram to see where they lead to.

 

Thanks to everyone who replied so quickly to this thread! I couldn't find any issues with any of the loom. This morning my new LED replacements for the stop/tail bulbs arrived (this was an inexpensive test to make sure none of the bulbs were faulty before taking to be diagnosed expensively)... Popped all the bulbs out and noticed one of them was a single filament compared to the normal double filament - this one also had some burn marks on the contacts in the connector. Scrubbed them with cotton ear buds and ethanol, popped all the new bulbs in and voila! All problems now cleared, brake light switch is no longer erroring (according to my cheap bluetooth diagnostic tool) and light come on and brakes can be depressed without tripping the HDC fault.

Pleased to consider this thread closed now! Merry Christmas everyone, lets hope 2021 is a much better year!

 

Thanks for the update and glad to hear you fixed the problem so quickly. I have been considering LED bulb replacements, where did you get yours from if I may ask? Thanks in advance, Merry Christmas to all... Eric...