NFav · Nov 9, 2017

2001 model TD5
Car unlocks on the remote key fine.
Starts up fine, but the hazards come on when you start sometimes. Worst in cold or cold damp mornings.
Have tried searching the forum for answers, so I have bypassed the underbonnet immobiliser and thought that had done.
2 days later just the same.
I have the BCU hanging down now, all nice and dry, no signs of dampness in that area at all.
My diagnostic kit wont give me any fault codes or anything for the BCU (maybe these don't log fault codes anyway) all the actuations seem to work when I command.
The only way of stopping the hazards flashing sometimes is to lock and unlock the car and start the engine. Sometimes the only way is disconnect the BCU.
I'm suspecting the BCU but would like to know of any test I can do confirm this.
Any help appreciated
Thanks

brian47 · Nov 9, 2017

You are correct to assume that the BCU controls the direction indicators and hazard lights, but the actual switching of the lights is done by the IDM (Intelligent Driver's Module) which is on the back and part of the fuse board below the steering column.
The usual fault with the IDM is moisture ingress, so you should check that area carefully.

sierrafery · Nov 9, 2017

NFav said:
... so I have bypassed the underbonnet immobiliser...

what's that and how did you bypass it?

and aamof the BCU doesnt have a fault code memory

NFav · Nov 10, 2017

sierrafery said:
what's that and how did you bypass it?

Sorry, bad description / wrong wording. inertia switch in the engine bay

brian47 · Nov 10, 2017

NFav said:
Sorry, bad description / wrong wording. inertia switch in the engine bay

Somebody has to ask, why bypass the inertia switch? Also what made you decide that the inertia switch was anything to do with the hazard indicators?
From what I can see, the hazard indicators work through the BCU/IDM and the inertia switch works on the Engine ECU.

NFav · Nov 10, 2017

brian47 said:
Somebody has to ask, why bypass the inertia switch? Also what made you decide that the inertia switch was anything to do with the hazard indicators?
From what I can see, the hazard indicators work through the BCU/IDM and the inertia switch works on the Engine ECU.

Because when the inertia switch is triggered it brings on the hazard warning lights but still allows the engine to run.
It seemed to fit the symptoms I have with this car, it was an easy thing to check and eliminate.

NFav · Nov 10, 2017

brian47 said:
You are correct to assume that the BCU controls the direction indicators and hazard lights, but the actual switching of the lights is done by the IDM (Intelligent Driver's Module) which is on the back and part of the fuse board below the steering column.
The usual fault with the IDM is moisture ingress, so you should check that area carefully.

Thanks for that information Brian.
I removed the fusebox and opened the box - no sighns of any dampness or water staining. I the swapped the fuse box with known good one and the fault is still present. Just to double check I fitted the fuse box from the poorly vehicle onto the good one and the fault didn't present itself on the good vehicle.

Thanks for your help but still trying

Landmark2 · Nov 10, 2017

Hi, Could it be simply a faulty hazzard light switch?

sierrafery · Nov 10, 2017

NFav said:
... when the inertia switch is triggered it brings on the hazard warning lights but still allows the engine to run.
....

that's completely wrong, cos if it was as you say that switch would not fit it's official name: inertia fuel cut-off switch which is on the main relay's coil so if it's tripped beside the hazards it cuts the ECU's and the fuel pump's feed too.... your next step should be to rule out the BCU too

NFav · Jan 22, 2018

Well folks, I've finally got to the bottom of this problem. Or at least some one in Holland did, but as he's an Englishman he can't speak Dutch and he posted the results of his identical problem in English on a Dutch LR forum (luckily).
The wire from the engine bay fuse box to the interior fuse box / IDM. Connector C0605, pin 4 to connector C0586 pin12, this wire had a high resistance (I can't remember the reading but way over 0.5ohm). So I chopped each end of the wire and soldered in a new section - problem solved.
Easy when you find the fault.
Thanks for everyones suggestions, I'm just pleased I can finally post up the fix

NFav

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