led's faint glow when off.

[VVC-Geeza]

I recently upgraded the courtesy light bulb in my 200 coupe to an led one.
I've found that as the light goes out a faint glow still remains.I wondered if this is normal and also whether it would cause battery drain.

I found this info on another forum,it seems it's quite common and nothing to worry about
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Why do the LEDs look like they are still on after I turn off my vehicle?

There are two situations in which your LEDs may stay on after your vehicle has been turned off. If you vehicle has auto dimming lights, your LED lights will gradually dim before shutting off completely. In the other situation, most vehicles, even when the vehicle engine is off, continues to send a small amount of current through the electrical circuits. This small amount of current is enough to turn the LEDs on to a very dim level. This however would not drain your vehicle battery since the same amount of current is traveling through the circuit whether you have halogen or LEDs.


The reason that some LED lights still glow and others don't is if the the car has canbus technology or not. If it does (which virtually all cars since the turn of century have), then the canbus technology can tell if a bulb is burnt out seeing that no output is coming. This is where you get hyper flashing, and as everybody has said, some LEDs are below that threshold and you still get the hyper flashing. Also this technology essentially runs the small amount of current when your car is off and some LEDs stay very dimly lit because it doesn't take much to get them going unlike halogens.

So lately LED manufacturers have been building "canbus" LEDs, which is essentially saying they built them to work better with the car technology. These LEDs won't give you the hyper blinking error because they have built in resistors, and they will shut completely off when the car is turned off because they make the threshold of current have to be higher in order to light the bulbs.

If anyone gets LEDs they should check to see if they are canbus or not. Precision LED and Vled but only sell the canbus ones I believe, which is good for all of us.

Basically our cars are smarter than the LED manufacturers and technology in LEDs has just started catching back up.

[Avulon]

Originally Posted by VVC-Geeza

Basically our cars are smarter than the LED manufacturers and technology in LEDs has just started catching back up.

No, it's just that the canbus technology was designed for power hungry filament type bulbs - An LED draws so little current that to a system designed to detect a broken filament - then that is what it looks like. Making them 'Canbus friendly' is making them pull as much electricall current as a filament bulb by placing a resistor in parralell with the LED. Making the LED pointless as a power saving measure.

The good news is that very few cars are going to use canbus bulb out detection for the courtesy light. It's much more likely a case of the courtesy lamp using a dimmer circuit with capacitors and the switching being done in the earth line. See here for an explanation

[VVC-Geeza]

Are they correct in saying that this slight glow will not cause battery drain?

I can't imagine it is drawing any more current than say a clock or flashing alarm led.

[HarryM1BYT]

Originally Posted by VVC-Geeza

Are they correct in saying that this slight glow will not cause battery drain?

I can't imagine it is drawing any more current than say a clock or flashing alarm led.

They will draw some current, but the amount will be tiny.

Avulon is correct in his suggestion that it is very unlikely that any car will monitor courtesy lights via can-bus - why would they need to?

His link to an explanation is wrong - that is common problem in 240v mains circuits, where some sort of sensor (PIR/) or remote control, is wired in series with lights, as a means to operate, where there is no accessible neutral. Fluorescent lights might flash or light dimly, as will CFL's and LED's, because current has to flow through the lamp, even when off, to power the extra item. Possibly the thyristor, or what ever it uses to do the switching.

None of that applies to your courtesy lights - I have LED's fitted and mine do not glow, so my best guess is that you have some leakage appearing across the body control units courtesy light switching system.

[Avulon]

Originally Posted by HarryM1BYT

They will draw some current, but the amount will be tiny.

Avulon is correct in his suggestion that it is very unlikely that any car will monitor courtesy lights via can-bus - why would they need to?

His link to an explanation is wrong - that is common problem in 240v mains circuits, where some sort of sensor (PIR/) or remote control, is wired in series with lights, as a means to operate, where there is no accessible neutral. Fluorescent lights might flash or light dimly, as will CFL's and LED's, because current has to flow through the lamp, even when off, to power the extra item. Possibly the thyristor, or what ever it uses to do the switching.

None of that applies to your courtesy lights - I have LED's fitted and mine do not glow, so my best guess is that you have some leakage appearing across the body control units courtesy light switching system.

Don't forget that the courtesy lights on the 75 are driven by a pwm circuit to control the dimming function. So it is one possible explanation. The other being some minor current leakage as you you suggest - aged transistor switching and all that..

[VVC-Geeza]

Originally Posted by Avulon

Don't forget that the courtesy lights on the 75 are driven by a pwm circuit to control the dimming function. So it is one possible explanation. The other being some minor current leakage as you you suggest - aged transistor switching and all that..

Just a quick reminder the issue is on my 1998 200 coupe not my 75.Don't know if technology was different back then regarding car lighting circuits?The OE halogen bulb certainly didn't remain lit at all.

[HarryM1BYT]

Originally Posted by VVC-Geeza

Just a quick reminder the issue is on my 1998 200 coupe not my 75.Don't know if technology was different back then regarding car lighting circuits?The OE halogen bulb certainly didn't remain lit at all.

Thanks, I had already spotted the 200, but made the assumption that it would be not much different to the 75.

If it concerns you, if you think the discharge is of concern -try measuring it. Pull the fuse and put a meter across the fuse socket.

[steve-45]

I get the same slight glow with the LED's fitted to the courtesy light of my 45, which is more likely to have the same control circuitary as your 200.

[VVC-Geeza]

Originally Posted by steve-45

I get the same slight glow with the LED's fitted to the courtesy light of my 45, which is more likely to have the same control circuitary as your 200.

I'm about to upgrade the one in my 45 to an led so I'll know what to expect

You don't mention any battery drain so I'm assuming all is well.

[Arryhall]

I replaced all my GU10's in my house with LED lamps, and when I turn the lights off, the LED's glow for a while. The standard halogen ones do not, so I presume it's something to do with the LED's themselves.