LED headlights got the pro's puzzled

[Dellmassive]

Keep at it..

I still think it's a problem with powers and grounds.

You gave the light unit a additional ground, that's good.

Id also try adding in a temp +12v main power feed for testing.

Use the scope.meter to log the +12v to see if you get a drop out or blip.

 

[Dav-Tec]

Ok gonna spend a few hours on it tomorrow before my night shift. Got.to be ground surely each lights terminal 56b wire is fed from a different plug so separate wires

 

[Dav-Tec]

So update.

Whilst ordering another more advanced oscilloscope (Picoscope 2204a, I'm determined to find this bugger) the passenger dipped beam turned off for a good 10 seconds so dashing in with my Multimeter revealed the cable for the dipped beam iirc pin 6 dropped to 8.5v!

Questions are, why? why does it effect both lights? And why can it happen to one light or the other independently?

Customer is collecting it back Tuesday

 

[Dellmassive]

Good detective work.

The BCM has multiple power feed that run multiple outputs.

Possibly corosion or a fuse holder with a spread pin.

A poor ground? Or corroded ground.

Remember a poor connection causes high resistance.

High resistance causes heat when current is flowing.

Heat will cause thermal expansion .... Ie fuse in holder.


As this has happened with two BCM it's external to that.

As you have fitted a temp new ground...


I would start investigating the power side..... From battery to fuse to BCM to fuse to light........

A good wiggles test everywhere ..... And especially at the fuse and fusebox.

 

[Dav-Tec]

So another day and more testing.

Stripped the comfort dash out and the fuse box. Found some additional wiring for interior lights etc but nothing I'd consider a problem.

Found fuse SC3 does the passenger side dipped beam and SC41 does the drivers side dipped beam. So can't see it being a power issue 2 separate fuses feeding 2 separate plugs on the BCM I did check it all over and couldn't find anything untoward.

More ground testing and found the results in the picture. I connected a jump lead directly from the battery negative direct to the drivers side chassis to engine earth point and it made no difference to the results so the main ground and all other grounds linking the engine etc are good.

Results to me are a little out there. Found battery neg to engine ground was around 2 ohms with the key off but turn the ignition on and it jumps to 10.89 ohms not sure how that works but I have just done a 12 hours night shift and by the time I got to bed I'd been up just shy of 24 hours and then was up and working on the van after 5 hours sleep so not firing on all cylinders.

I'm still thinking it's a ground issue. Connected my new Picoscope up and tested the PWM wire and the 12v wire feeding the dipped beam and nothing untoward there either.

 

[mmi]

Found battery neg to engine ground was around 2 ohms with the key off but turn the ignition on and it jumps to 10.89 ohms not sure how that works

I'm afraid measuring resistance of "live" circuit just doesn't work. I would say both values are incorrect because even quiescent not to mention ignition current through the cable causes a voltage loss thus confusing the resistance measurement.

 

[Dav-Tec]

I'm afraid measuring resistance of "live" circuit just doesn't work. I would say both values are incorrect because even quiescent not to mention ignition current through the cable causes a voltage loss thus confusing the resistance measurement.

I wasn't measuring a live circuit I measured from the battery neg to the enging ground strap and in a continuity check to see what the continuity was like in various places. The voltage on the oscilloscope was being measured to try and capture what was happening when the fault occurs to try and determine if its a power/ground fault or some sort of signal fault but this time round it hasn't happened so still none the wiser

 

[mmi]

I measured from the battery neg to the enging ground strap

Like this?

 

[Dav-Tec]

Yes buddy

 

[mmi]

Multimeters measure resistance by injecting a small current into the circuit, and then measuring the voltage drop across those points in the circuit, having the circuit powered on will cause interference with the resistance measurement and will cause bad readings. Even the quiescent current of the van (approx. 30 mA) is much larger than what the multimeter is capable of injecting.

One way to check the existence of disturbing currents is to swap the multimeter leads (common and +) - and verify readings. In presence of external factors the reading will change dramatically - even negative resistance could be observed.

Anyways, that's just to explain the different resistance values observed with/without ignition on - not to get distracted with strange results.

---

Have you tried warming up the headlight (power module) with heat gun - just to see if that would have any effect on blinking/flashing "rate"? Perhaps combined letting starter battery discharge down to 12 Volts (having lights and ignition on), and the same keeping battery at 14.8 Volts by charger?

 

[Paynewright]

Multimeters measure resistance by injecting a small current into the circuit, and then measuring the voltage drop across those points in the circuit, having the circuit powered on will cause interference with the resistance measurement and will cause bad readings. Even the quiescent current of the van (approx. 30 mA) is much larger than what the multimeter is capable of injcecting.

One way to check the existence of disturbing currents is to swap the multimeter leads (common and +) - and verify readings. In presence of external factors the reading will change dramatically - even negative resistance could be observed.

Anyways, that's just to explain the different resistance values observed with/without ignition on - not to get distracted with strange results.

---

Have you tried warming up the headlight (power module) with heat gun - just to see if that would have any effect on blinking/flashing "rate"? Perhaps combined letting starter battery discharge down to 12 Volts (having lights and ignition on), and the same keeping battery at 14.8 Volts by charger?

I remember Dad telling me the main reason meters have a battery in them is for testing resistance, to provide this current.

 

[Dav-Tec]

Have you tried warming up the headlight (power module) with heat gun - just to see if that would have any effect on blinking/flashing "rate"? Perhaps combined letting starter battery discharge down to 12 Volts (having lights and ignition on), and the same keeping battery at 14.8 Volts by charger?

The lights where swapped previously from another van without any issues. I haven't tried doing what you suggested. I've had the lights on with and without a charger and they do it regardless. I've had the engine run for about 20 mins and it never did it, yet the owner could be driving some where and it would. Yet it can sit on my driver for an 1 hour and nothing then suddenly 2 or 3 times in the space of 10 mins. Sometimes it appears to go off and stay off for several seconds and back on again not just the blink of an eye.

Would you suggest ground testing with the battery disconnected?

I'm aware of how a multimeter works just didn't think it would cause that much interference but the theory makes sense.

 

[Alster]

If you connect your multimeter to the battery neg and the earth (as the picture) but instead of setting it to ohms set it to volts it should read zero or there about then put the lights on to give it a load -the voltage reading should stay very low. If you’ve got a poor connection the high resistance will act like a shunt and the voltage will rise. Hope this makes sense!

 

[mmi]

Would you suggest ground testing with the battery disconnected?

No, not the prime suspect as van starts, runs, lights work... most of the time - unless by switching on/off consumers (blower, heaters, etc) have an effect.

Can you do a MIN/MAX recording (possibly even with multimeter)- to catch short glitches. I would hook up into headlight connector and try to verify the "shut off" happens in the actual feed at the connector between. Can you back probe into +12V and GND in the headlight connector?

 

[Dav-Tec]

Yeah I have some insulation piercing clamps I can attach whilst capturing the voltage.

I'll test the shunt idea out tomorrow. I have a 12 hour night shift to do and then got a customers van in at 10.30 lol so it'll be after that's done

 

[Dav-Tec]

So, checked the battery (New shiny Snap On goodies arrived today!) and it's spot on. I checked the voltage between the battery negative and the engine mount ground as suggested and I Had 0.0029VDC with the ignition off and when I turned it on it rose to 0.0070VDC and held at 0.0066VDC so I'm happy there's no hi resistance.

The light did do the fault and the scope dropped from 12.32V to mid 2V territory for a split second but like a muppet I didn't save the screen data and lost it so need to recapture it tomorrow after I've finished kicking my self. Also I did manage to capture the voltage at the back of the headlights and it floats around 2V and does go on and off as expected with the ignition. See scope photos attached

It still doesn't explain why the lights can do this fault independent of each other. Also could a faulty headlight range control module cause this fault? I'm assuming not but a mate chucked that idea in the mix so just wondering if he has a point.

I appreciate everyone's time and input so far.

Cheers Chris

 

[JOG]

This is an intriguing issue. Nice to see that @mmi is on the case - the diagnostics guru!

 

[Paynewright]

Has it had anything else added to the lighting circuits? Maybe one of those aftermarket light sensitive auto switches??

 

[mmi]

The light did do the fault and the scope dropped from 12.32V to mid 2V territory for a split second

Where exactly this was measured?

 

[Dav-Tec]

I connect the scope at the plug of the drivers and passengers headlight with the lights still plugged in so everything is under load. Pin 6, yellow wire that supplied the dipped beam on the drivers headlight