BECM, Battery, Sync and LEDs

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D

damlimey

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Hi all,

I recently posted concerning my indicators which had turned themselves on with no flashing while the vehicle was left unattended for a few days.

To my surprise, all I needed on return was a jump start and there were no EKA/ignition issues just a dead battery.

At the end of the thread of advice I received while anticipating the worse, a senior member 'Canyon' says that the BECM is going out of sync, symptoms are all there, change the battery straight away'.

When the RAC bump started me, that was their suggestion too.

The battery is a big Bosh which I bought new less than two years ago and so I wasn't expecting any problems in that department for a few years yet.

However...

I recently started upgrading my lamps with LEDs. First it was the interior courtesy lights and just a week or so ago, the running lights.

So the the Canbus system doesn't see the filament-free LED as a blown bulb, these LEDs are fitted with what amounts to a resistor which simulates the circuit and load of a filament bulb.

So to my question... Could the recent conversion to LEDs have affected the BECM and set it on a wobble? Only hours after fitting the running light LEDs, I needed to re-sync the key.

Are all these coincidences and I should just go get a new battery after only 18 months which I'll do anyway, or is there something to my LED theory?

Ta!

D
 
I have no idea - but why would you add more electronics to an already electronically unreliable vehicle?? Gluten for punishment would be my guess!!!

In all seriousness, I applaud anyone with the stones to do such work as I shy away from anything that doesn't require a spanner and hammer...

Good Luck, but if the problems started on fitment of the LED's I think that would be a good place to start!
 
If they are the resistor type, and pulling the same load then I can't see it, as it would be the same as putting a filaments type lamp in , but this is a p38 and anything could happen, I reckon coincidental, others may suggest otherwise
 
damlimey said:
Hi all,

I recently posted concerning my indicators which had turned themselves on with no flashing while the vehicle was left unattended for a few days.

To my surprise, all I needed on return was a jump start and there were no EKA/ignition issues just a dead battery.

At the end of the thread of advice I received while anticipating the worse, a senior member 'Canyon' says that the BECM is going out of sync, symptoms are all there, change the battery straight away'.

When the RAC bump started me, that was their suggestion too.

The battery is a big Bosh which I bought new less than two years ago and so I wasn't expecting any problems in that department for a few years yet.

However...

I recently started upgrading my lamps with LEDs. First it was the interior courtesy lights and just a week or so ago, the running lights.

So the the Canbus system doesn't see the filament-free LED as a blown bulb, these LEDs are fitted with what amounts to a resistor which simulates the circuit and load of a filament bulb.

So to my question... Could the recent conversion to LEDs have affected the BECM and set it on a wobble? Only hours after fitting the running light LEDs, I needed to re-sync the key.

Are all these coincidences and I should just go get a new battery after only 18 months which I'll do anyway, or is there something to my LED theory?

Ta!

D
Click to expand...


High brightness LED's run on 3 volts not 12 and require a stable voltage level, in the past a series resistor was sufficient but a lot of data sheets specify a stabilsed supply, so it's possible a switch mode supply is bullt into the LED lamp, this could cause interferance with the car electronics. Only a guess though. Put the correct bulbs back and see what happens.
No CAN BUS on the P38.:)
 
Pointless? How else would you fool the BECM? LEDs come fitted with resistors now and they have some advantages over the conventional bulbs. I like to experiment with new things to see if they improve my life and experience in a positive way. Some things do and some things don't but at least I've tried and I've learnt something along the way.

Here for example, I've learnt that maybe, LED bulbs should be left in a box and not my car. That's okay 'cause I know that now and won't die wondering...

Have I also learnt that even a brand new Bosch battery might need replacing in less than two years because of the sensitivity of the BECM to voltage? We'll see.

Ah, life is short. But when we teach others, we become immortal!

D
 
I fitted these in place of the side lights last week. No issues so far, other than getting a warning for one of the tail lights lights not working intermittantly, but its been doing that for weeks. So I've ordered a couple more. They look fine in daylight, not had chance to view them at night yet. I thought worth a try as they are so cheap but have good reviews (some LED's have crap reviews).

2 x 5 SMD LED 360° Ultra White Bulbs / T10 Side Repeater Bulbs / Replacement for 501 W5W 168 194 Bulbs (1 pair 2 units): Amazon.co.uk: Lighting
 
I've been running LED sidelights and internal lights (and in the boot, the passenger footwell and under the side steps) for over a year now with no issues.
I can't believe that LED lights can affect your battery as, even if there was any interference, then it would only happen when your lights are on, not when you've been parked up for a while.
I'd rather check the usual P38 suspects; RF receiver, alternator, fusebox and battery (regardless of it's make & age.)
 
Thanks for all that input guys, though I still have a couple of little questions... A couple of references to the fusebox (under bonnet) have been made but I don't quite understand what to look for. The relays have always had a bit of an 'electrical' smell when you lift the lid of but there are no indicator related relays under there so what might be a symptom in there?

I have just noticed that the hevac backlight dims when I put the brakes on...

And... Is the becm really that sensitive to the battery condition? what doesn't it like? -.2v or -.5v more/less...

Thanks again.

D
 
damlimey said:
Thanks for all that input guys, though I still have a couple of little questions... A couple of references to the fusebox (under bonnet) have been made but I don't quite understand what to look for. The relays have always had a bit of an 'electrical' smell when you lift the lid of but there are no indicator related relays under there so what might be a symptom in there?

I have just noticed that the hevac backlight dims when I put the brakes on...

And... Is the becm really that sensitive to the battery condition? what doesn't it like? -.2v or -.5v more/less...

Thanks again.

D
Click to expand...

Sounds like your fuse box is toast, could well be the source of all your problems.
All the ECU's are sensitive to voltage, in particular to voltage fluctuations where the voltage will momentarily drop below a viable level. If the battery is weak this is more likely to be a problem. Bad connections have a similar effect, so high resistance connections in the fuse box not only cause the fuse box to over heat, they cause volt drop which affect the ECU's.
 
damlimey said:
So, should I replace the whole under bonnet fuse box and re-populate it or just re-populate the existing fuse box? The poor connectivity must refer to the relays, is that correct? So I should replace all the relays?

Blimey...

D
Click to expand...

Not had a similar issue myself (YET... touches wood) but I think Data would reccommend replacing the fuse box and re-fit original relays unless they look faulty after a bench test.
 
I believe the Fusebosx issue is the actual fusebox itself, the boards warp and crack under the heat causing havoc....

As Stufer and Datatek have said, replace the whole box and repopulate with your current fittings....
 
damlimey said:
So, should I replace the whole under bonnet fuse box and re-populate it or just re-populate the existing fuse box? The poor connectivity must refer to the relays, is that correct? So I should replace all the relays?

Blimey...

D
Click to expand...

Re-use the relays, just check the contact are not blued with heat and the plastic base has not melted. Same for fuses:)
 
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